지난번 글에서 설명드린 **‘시킴산 경로(shikimate pathway)’**를 기억하시나요?
이 경로는 식물이 생존에 필수적인 방향족 아미노산(트립토판, 티로신, 페닐알라닌)을 합성하는 데 사용됩니다.
그리고 글리포세이트는 바로 이 시킴산 경로를 표적으로 합니다.
이에 어떤 분이 이렇게 질문하셨습니다.
“그렇다면 시킴산 경로가 인간에게는 존재하지 않는데, 글리포세이트가 어떻게 인체 유해성과 관련이 있다는 거지요?”
참으로 ‘위대한 질문’이라고 생각합니다.
지금부터 각 잡고 이 질문에 대한 답을 자세히 풀어보겠습니다.
1. 시킴산 경로와 인체 유해성: 장내 미생물(Gut Microbiome)이 핵심!
먼저 시킴산 경로는 식물과 특정 미생물에게만 존재합니다.
따라서 글리포세이트가 사람에게 직접 해롭다는 사실을 이해하려면, 우리는 바로 우리의 **‘장내 미생물(Gut Microbiome)’**에 주목해야 합니다.
우리 장 속에는 수많은 미생물이 공생하고 있는데, 이들 중 상당수는 시킴산 경로를 가지고 있어 필수 아미노산을 합성합니다.
그런데 우리가 글리포세이트가 잔류된 식품, 예를 들면 수입 밀가루나 GM 작물을 먹인 육류를 섭취할 때, 이 화학물질은 소화되지 않은 채 장으로 들어옵니다.
그리고 인간의 장 속에 있는 다양한 미생물(세균, 곰팡이 등)은 식물과 마찬가지로 시킴산 경로를 가지고 있어서, 우리에게 필요한 아미노산(트립토판, 티로신, 페닐알라닌)을 만듭니다.
문제는 글리포세이트가 이 장내 미생물의 시킴산 경로에 영향을 미쳐 필수 아미노산 합성을 방해한다는 점입니다.
이로 인해 유익한 장내 미생물(예: 락토바실러스, 비피도박테리움)의 성장은 억제될 수 있습니다.
또한 시킴산 경로가 없거나 글리포세이트에 내성이 있는 유해균(예: 클로스트리디움 보툴리눔, 살모넬라 등)은 오히려 증식할 수 있습니다.
결과적으로 이러한 불균형은 **‘장내 미생물총 이상증(dysbiosis)’**을 유발하게 됩니다.
그리고 장내 미생물이 만드는 트립토판, 티로신, 페닐알라닌은 인간에게 매우 중요한 영양소입니다.
특히 트립토판은 신경전달물질인 세로토닌의 전구체이므로, 미생물의 시킴산 경로가 억제되면 이 아미노산의 체내 가용성도 줄어들 수 있습니다.
더 나아가 일부 연구는 글리포세이트가 사람의 간에 있는 사이토크롬 P450(CYP) 효소 시스템을 억제할 수 있다고도 주장합니다.
이 CYP 효소는 체내 독소, 약물, 환경 오염 물질 등을 해독하고 대사하는 데 아주 중요합니다.
만약 이 효소 시스템이 억제되면, 우리 몸의 독소 배출 능력이 떨어져 독소 축적이 늘어날 수 있습니다.
인용 논문 1:
Samsel, A., & Seneff, S. (2013). Glyphosate’s suppression of cytochrome P450 enzymes and amino acid biosynthesis by the gut microbiome: pathways to modern diseases. Interdisciplinary Toxicology, 6(4), 163-184.
이 논문은 글리포세이트가 장내 미생물의 시킴산 경로를 억제하여 필수 아미노산 합성을 방해하고, 더 나아가 인간의 CYP 효소를 억제하여 독소 해독 능력을 저하시킬 수 있음을 주장합니다.
그리고 이로 인해 자폐증, 치매 등 다양한 만성 질환이 발생할 수 있다고 이야기합니다.
암 발생 기전(간접적 연관성)
글리포세이트가 직접적으로 인간 세포의 DNA를 손상시켜 암을 유발한다는 명확한 기전은 아직 밝혀지지 않았습니다.
하지만 다음과 같은 간접적 기전들이 암 발생과 관련될 수 있다는 가설이 계속 제시되고 있습니다.
우리 몸의 장내 미생물총의 불균형은 만성 염증, 면역 기능 이상, 독소 생성 증가 등 여러 방식으로 암 발생 위험을 높일 수 있습니다.
건강한 장내 환경은 발암 물질의 흡수를 줄이고 면역 방어 기능을 강화하는 데 중요합니다.
또한 일부 연구는 글리포세이트가 세포 내 산화 스트레스를 증가시킬 수 있다고 제시합니다.
이 산화 스트레스는 활성산소가 과도하게 생성되어 세포를 손상시키는 상태로, DNA 손상으로 이어져 암 발생 위험을 높일 수 있습니다.
만약 CYP 효소 억제 가설이 사실이라면, 우리 몸의 해독 능력이 떨어져 발암 물질이 체내에 더 오래 머물게 됩니다.
이 과정은 결국 세포 손상과 암 발생 위험을 높이는 결과를 초래할 수 있습니다.
또한 장내 미생물 불균형과 다른 기전들을 통해 면역 체계가 교란되면, 암세포를 감시하고 제거하는 중요한 면역 기능이 약화될 수 있습니다.
요약:
글리포세이트의 발암 가능성(IARC Group 2A 분류)은 직접적인 DNA 손상보다는, 주로 장내 미생물 교란, 산화 스트레스 증가, 해독 능력 저하, 면역 체계 교란 등 간접적 기전으로 설명되고 있습니다.
이는 여전히 많은 연구가 진행 중인 분야이기도 합니다.
2. 자폐증, ADHD, 치매, 파킨슨병과의 연관성 기전
자폐증, ADHD, 치매, 파킨슨병 등 다양한 신경계 질환과의 연관성은 장내 미생물총, 신경전달물질, 해독 능력, 염증 반응 등과 긴밀하게 연결되어 설명됩니다.
물론 이 질환들은 복합적인 원인을 가지지만, 글리포세이트 노출이 하나의 환경적 요인으로 작용할 수 있다는 가설이 제기되고 있습니다.
공통적으로 제안되는 기전
장-뇌 축 교란(Gut-Brain Axis Disruption):
- 장내 미생물 변화: 글리포세이트가 장내 미생물의 균형을 깨뜨리면, 유익균 감소와 유해균 증가로 인해 장벽 투과성이 높아지는 **‘새는 장 증후군(Leaky Gut Syndrome)’**이 발생할 수 있습니다.
- 신경전달물질 영향: 장내 미생물은 세로토닌, 도파민 등 여러 신경전달물질과 그 전구체를 생성합니다. 글리포세이트가 장내 미생물의 시킴산 경로를 억제하면 트립토판(세로토닌 전구체)의 가용성이 줄어들 수 있습니다.
- 염증 및 독소 유입: ‘새는 장 증후군’을 통해 독소나 미생물 대사 산물이 혈류로 유입되면, 이는 **뇌 염증(neuroinflammation)**을 유발하여 신경계 질환 위험을 높일 수 있습니다.
인용 논문 2:
Seneff, S., Swanson, N., & Li, C. (2015). Glyphosate impairs the shikimate pathway in bacteria, fungi, algae, and archaea. In Bioactive Food Peptides in Health and Disease (pp. 577-628). Academic Press.
이 논문은 글리포세이트가 장내 미생물의 시킴산 경로를 교란하여 트립토판 등 필수 아미노산 생성을 저해하고, 이로 인해 신경계 질환과 연관될 수 있음을 심층적으로 다룹니다.
각 질환별 연관성
자폐증 (오티즘 스펙트럼 장애):
기전: 장내 미생물 불균형(특히 클로스트리디움 속 세균 증가), 비정상적인 세로토닌 대사, 뇌 염증 등이 자폐증 발병과 증상 악화에 연관된다는 가설이 있습니다.
또한 글리포세이트는 이러한 기전들에 영향을 미칠 수 있다는 보고가 있습니다.
예를 들어 장내 미생물이 트립토판을 적게 만들어내면, 세로토닌 합성이 감소할 수 있으며, 이는 신경 발달에 영향을 줄 수 있습니다.
인용 논문 3:
Shaw, W. (2013). Evidence of glyphosate in autism. Journal of Toxicology and Environmental Health, Part B, 16(2), 79-91.
참고로 이 논문은 학술적 논란 끝에 철회되었으나, 자폐증과 글리포세이트의 연관성에 대한 연구는 여전히 이어지고 있습니다.
특히 Seneff 등의 연구진이 이 분야에서 활발히 활동 중입니다.
ADHD (주의력결핍 과잉행동장애):
기전: 도파민과 노르에피네프린 등 신경전달물질의 불균형, 장내 미생물총 이상, 그리고 환경 독소 노출 등이 ADHD의 발병과 연관된다고 알려져 있습니다.
또한 글리포세이트가 이러한 경로에 영향을 줄 수 있다는 주장도 계속 제기되고 있습니다.
특히 장내 미생물 교란이 신경발달 장애의 위험을 높일 수 있다는 점이 주목받고 있습니다.
치매 (알츠하이머병 등):
기전: 뇌 염증, 산화 스트레스, 미토콘드리아 기능 이상, 그리고 아밀로이드 플라크 및 타우 단백질 축적 등이 치매의 주요 기전으로 알려져 있습니다.
이와 관련하여 글리포세이트가 이러한 요소들에 영향을 줄 수 있다는 초기 연구 결과들이 보고되고 있습니다.
예를 들어 산화 스트레스가 만성화되면, 뇌 세포의 손상이 가속화될 수 있습니다.
참고로 아밀로이드 플라크 축적이 치매의 주요 기전이라는 가설에 대해서는, 별도의 장에서 더욱 깊이 있게 다룰 예정입니다.
파킨슨병:
기전: 도파민성 신경세포의 손상, 알파-시누클레인 단백질의 비정상적 축적, 미토콘드리아 기능 이상, 그리고 산화 스트레스 등이 파킨슨병과 연관됩니다.
또한 글리포세이트가 도파민 신경세포 독성을 유발하거나, 미토콘드리아에 손상을 줄 수 있다는 동물 실험 결과들도 일부 발표된 바 있습니다.
이처럼 여러 연구가 서로 다른 기전을 통해 가능성을 제시하고 있지만, 아직은 명확히 확립된 인과관계라고 보기는 어렵습니다.
3. 학계의 입장과 연구의 한계
신경계 질환과 글리포세이트의 연관성은 현재 학계에서 매우 활발하게 연구되는 분야입니다.
하지만 몇 가지 한계점과 논쟁도 존재합니다.
우선 자폐증, ADHD, 치매, 파킨슨병 등은 유전적 요인, 환경적 요인, 생활 습관 등 다양한 요소가 복합적으로 작용하는 다인성(multifactorial) 질환입니다.
따라서 글리포세이트가 이들 질환의 ‘단독 원인’이라고 주장하기는 어렵습니다.
그리고 일부 연구에서는 글리포세이트와의 연관성을 발견하지만, 다른 연구에서는 연관성을 찾지 못하거나 오히려 상충되는 결과를 보고하기도 합니다.
이러한 차이는 연구 설계, 노출량, 대상 집단, 그리고 혼란 변수 통제의 차이에서 비롯될 수 있습니다.
또한 몬산토(현재 바이엘 소유) 측은 글리포세이트의 안전성을 지속적으로 옹호하고 있습니다.
그들은 이 제품이 수십 년간 광범위하게 사용되었음에도, 과학적으로 유해성이 명확하게 입증되지 않았다고 주장합니다.
그리고 회사는 이 제품 때문에 수많은 소송에 연루되어 거액의 배상금을 지급하고 있으며, 여전히 새로운 소송이 이어지고 있습니다.
이 부분을 어떻게 이해해야 할까요?
아스피린으로 잘 알려진 바이엘은, 몬산토를 인수하면서 거대한 부담을 떠안았습니다.
하지만 그들은 여전히 글리포세이트의 무해성을 주장하며, 동시에 다른 농약·제초제 기업까지 인수하는 전략을 선택했습니다.
이러한 결정은 단순히 한 제약회사의 이익 추구를 넘어, 산업 농업 시스템의 구조적 문제를 드러내는 사례이기도 합니다.
바이엘사에 대해서도 차후에 좀더 살펴볼 예정입니다.
결론: 끝나지 않는 과학적 논쟁과 우리의 선택
글리포세이트의 인체 유해성, 특히 신경계 질환과의 연관성은 여전히 진행 중인 과학적 논쟁입니다.
비록 시킴산 경로가 인간에게 직접 존재하지 않더라도, 장내 미생물총을 교란하고, 해독 능력에 영향을 주며, 산화 스트레스를 유발할 수 있다는 가설이 꾸준히 제시되고 있습니다.
이런 불확실성 속에서 우리는 어떻게 대응해야 할까요?
예방적 원칙(Precautionary Principle):
과학적 증거가 100% 확립되지 않았더라도, 잠재적 위험이 있다면 이를 예방하기 위한 조치를 취해야 한다는 원칙입니다.
특히 어린이나 임산부, 질병 혹은 질환을 진단받으신 분, 면역력이 취약한 계층에게는 더 중요하게 적용되어야 합니다.
정보의 비판적 수용:
전문가나 미디어의 정보를 맹목적으로 받아들이기보다는, 다양한 출처의 정보를 비판적으로 검토하고 스스로 판단하려는 노력이 필요합니다.
안전한 식품 선택:
글리포세이트 잔류 우려가 있는 식품(수입 밀, 옥수수, 대두, 렌틸콩 등)의 경우, 가능하면 유기농, Non-GMO, 또는 글리포세이트 프리 인증 제품을 선택하는 것이 잠재적 노출을 줄이는 좋은 방법입니다.
그리고 우리 국산 농산물과 제철 식품을 우선적으로 선택하는 것도 현명한 방법입니다.
지속적인 연구와 정책 변화 촉구:
학계에서는 더욱 심층적이고 독립적인 연구가 활발히 진행되어야 하며, 정부는 소비자의 안전을 최우선으로 삼아 화학물질 규제 및 식품 안전 기준을 강화해야 합니다.
마치 레이첼 카슨의 『침묵의 봄』이 DDT의 위험을 경고했듯이, 우리는 글리포세이트 같은 현대 화학물질이 우리의 **‘침묵의 장기’**와 신경계에 어떤 영향을 미치는지에 대해 끊임없이 질문하고, 더 나은 답을 찾아야 할 책임이 있습니다.
혹시, 올봄 미국에서는 제법 봄기운이 도는 법안이 통과되었다는 소식을 접하셨나요?
지역에 따라 여름 초입이거나 한여름일지 모르겠습니다.
그러나 철 지난 봄의 이야기라도, 그 내용이 모처럼 신선하기에 함께 나눌 수 있기를 바랍니다.
철 지난 봄 이야기를 궁금해 하면서, 셰익스피어의 “한여름 밤의 꿈”을 다시 뒤적여보셔도 좋겠습니다.
더불어, 멘델스존이 작곡한 “한여름 밤의 꿈”을 감상하며 궁금증을 키우는 것도 좋겠네요.
“결혼 행진곡”을 들으며 과거의 결혼 시절을 회상하거나, 미래의 결혼식을 상상해보아도 좋겠습니다.
이런 여유로운 마음과 꿈꿀 수 있는 순간들, 그리고 사소한 궁금증조차도 심신의 건강에 도움이 됩니다.
어쩌면 이런 말을 하실 분도 계시겠지요?
“난 이미 당신이 하는 경고에 대해 충분히 알고 있어요. 글리포세이트와 GM 작물 관련 식재료 따위, 우리 식탁에서 사라진 지 오래에요. 아무튼 염려해줘서 고마워요. 다른 이들은 몰라도 난 왠지 이런 글은 시간 낭비 같네요. 강아지와 공원 산책 후, 골프 약속이 있어서 그럼 이만 실례.”
다음 편 예고:
가능하면 강아지와 공원으로 산책 나가기 전, 혹은 골프장으로 향하기 전, 다음 글이 전달되기를 기대합니다.
다음 글은 “공원에서, 골프장에서 뜻밖에 만난 왠수?”를 주제로 이어가도록 하겠습니다.
참고문헌
- 저자: Mesnage, S., & Antoniou, M. N.
- 출처: Food and Chemical Toxicology, 2017.
- 제목: Ignoring the Obvious: The Scientific and Regulatory Non-Compliance of Glyphosate Risk Assessments.
- 내용 요약: 이 리뷰 논문은 글리포세이트의 독성 평가에 대한 기존 규제 프레임워크의 한계를 비판적으로 검토합니다. 특히 글리포세이트 제형에 포함된 다른 성분(계면활성제 등)의 독성 효과가 간과되고 있으며, 장기적이고 복합적인 노출에 대한 연구가 부족함을 지적합니다. 글리포세이트 단일 물질이 아닌 상업용 제형 전체에 대한 평가가 필요하다는 점을 강조합니다.
- 저자: Van Bruggen, A. H. C., He, M. M., Shin, K., Mai, V., Jeong, K. C., Finckh, M. R., & Gaskell, J. (2018).
- 출처: Environmental Pollution, 2018.
- 제목: Environmental and health effects of the herbicide glyphosate.
- 내용 요약: 이 논문은 글리포세이트의 환경 및 건강 영향을 광범위하게 검토합니다. 특히 토양 미생물, 수생 생태계에 미치는 영향과 함께 인간의 장내 미생물, 면역 시스템, 신경계에 대한 잠재적 영향을 다룹니다. 글리포세이트가 미생물에 미치는 영향이 먹이사슬을 통해 인간 건강에까지 연쇄적으로 영향을 줄 수 있다는 가능성을 제시합니다.
- 저자: Rueda-Ruzafa, L., Cruz, F., Roman, P., & Cardona, D. (2019).
- 출처: Environmental Research, 2019.
- 제목: Gut microbiota and neurological diseases: A systematic review and meta-analysis.
- 내용 요약: 이 체계적 문헌고찰 및 메타분석은 장내 미생물과 다양한 신경계 질환(자폐증 스펙트럼 장애, 파킨슨병, 알츠하이머병, 다발성 경화증 등) 간의 연관성을 탐구합니다. 글리포세이트를 직접 다루지는 않지만, 장-뇌 축 교란이 신경계 질환 발병에 중요한 역할을 한다는 일반적인 원리를 뒷받침하여 글리포세이트가 장내 미생물 교란을 통해 신경계에 영향을 줄 수 있다는 가설의 배경 지식을 제공합니다.
- 저자: Mills, K., Niedzwiecki, A., & Rath, M. (2020).
- 출처: Journal of Cellular and Molecular Medicine, 2020.
- 제목: Review on the mechanisms of action of glyphosate in mammalian systems and its potential link to cancer and other diseases.
- 내용 요약: 이 리뷰는 글리포세이트가 포유류 시스템에서 작용하는 여러 메커니즘을 상세히 설명하며, 특히 미토콘드리아 기능 장애, 산화 스트레스 유발, DNA 손상(간접적) 가능성 등을 강조합니다. 또한 글리포세이트가 암을 포함한 다양한 만성 질환과 연관될 수 있다는 증거들을 종합적으로 검토하며, 추가적인 독립적인 연구의 필요성을 역설합니다.
- 저자: Li, C., Seneff, S., & Swanson, N. (2021).
- 출처: Environmental Science and Pollution Research, 2021.
- 제목: Glyphosate, aluminum, and fluoride: A trifecta of toxicity in neurological disease?
- 내용 요약: 이 논문은 글리포세이트가 알루미늄 및 불소와 같은 다른 환경 독소와 함께 신경계 질환에 시너지 효과를 낼 수 있다는 가설을 탐구합니다. 특히 글리포세이트가 금속 이온을 킬레이트(결합)하는 능력과 미생물군집에 미치는 영향을 통해 신경 독성 경로가 강화될 수 있음을 제안하며, 복합적인 환경 노출의 중요성을 강조합니다.
Late Lessons from Early Warnings: The Ongoing Controversy of Chemical Substances, Glyphosate, and Our Health
Do you remember the ‘shikimate pathway’ we discussed in the previous article? This pathway is used by plants to synthesize essential aromatic amino acids (tryptophan, tyrosine, phenylalanine) vital for their survival. And glyphosate specifically targets this shikimate pathway.
Someone posed a great question: “If the shikimate pathway doesn’t exist in humans, how is glyphosate harmful to human health?” This is indeed a “great question”!
Let’s thoroughly address this question in detail.
1. Shikimate Pathway and Human Health Effects: The Gut Microbiome is Key!
First, the shikimate pathway exists only in plants and certain microorganisms. Therefore, to understand how glyphosate can be directly harmful to humans, we must focus on our ‘gut microbiome.’
Our intestines harbor countless microorganisms in symbiosis, and a significant number of them possess the shikimate pathway to synthesize essential amino acids. When we consume food contaminated with glyphosate residues—for example, imported wheat flour or meat from animals fed GM crops—this chemical enters our intestines undigested.
Just like plants, various microorganisms (bacteria, fungi, etc.) in the human gut have the shikimate pathway, which they use to produce amino acids (tryptophan, tyrosine, phenylalanine) that are crucial for us. The problem is that glyphosate affects the shikimate pathway of these gut microbes, disrupting their synthesis of essential amino acids. This can suppress the growth of beneficial gut microbes (e.g., Lactobacillus, Bifidobacterium). Conversely, harmful bacteria (e.g., Clostridium botulinum, Salmonella), which lack the shikimate pathway or are resistant to glyphosate, may proliferate.
Consequently, this imbalance can lead to ‘gut microbiome dysbiosis.’ And the tryptophan, tyrosine, and phenylalanine produced by gut microbes are extremely important nutrients for humans. Specifically, tryptophan is a precursor to the neurotransmitter serotonin; thus, inhibition of the microbial shikimate pathway can reduce the bioavailability of this amino acid in the body.
Furthermore, some studies claim that glyphosate can inhibit the cytochrome P450 (CYP) enzyme system in the human liver. This CYP enzyme is crucial for detoxifying and metabolizing toxins, drugs, and environmental pollutants in the body. If this enzyme system is suppressed, our body’s ability to excrete toxins may decrease, leading to increased toxin accumulation.
Citation 1: Samsel, A., & Seneff, S. (2013). Glyphosate’s suppression of cytochrome P450 enzymes and amino acid biosynthesis by the gut microbiome: pathways to modern diseases. Interdisciplinary Toxicology, 6(4), 163-184. This paper argues that glyphosate can suppress the shikimate pathway in gut microbes, hindering essential amino acid synthesis, and further inhibit human CYP enzymes, thereby reducing detoxification capabilities. It also suggests that this can lead to various chronic diseases such as autism and dementia.
Cancer Development Mechanisms (Indirect Association) While a clear mechanism by which glyphosate directly damages human cell DNA to cause cancer has not yet been elucidated, indirect mechanisms are continuously being proposed as potentially related to cancer development.
Imbalance in our gut microbiome can increase cancer risk in various ways, including chronic inflammation, impaired immune function, and increased toxin production. A healthy gut environment is crucial for reducing the absorption of carcinogens and strengthening immune defenses.
Additionally, some studies suggest that glyphosate can increase intracellular oxidative stress. This oxidative stress, a state where excessive reactive oxygen species are generated, damages cells and can lead to DNA damage, thereby increasing cancer risk. If the CYP enzyme inhibition hypothesis is true, our body’s detoxification capacity would decrease, allowing carcinogens to remain in the body longer. This process could ultimately result in increased cell damage and heightened cancer risk.
Furthermore, if the immune system is disrupted through gut microbiome imbalance and other mechanisms, crucial immune functions that monitor and eliminate cancer cells may be weakened.
Summary: The probable carcinogenicity of glyphosate (IARC Group 2A classification) is explained by indirect mechanisms rather than direct DNA damage. These include gut microbiome disruption, increased oxidative stress, reduced detoxification capacity, and immune system dysregulation. This is still an area of active research.
2. Mechanisms of Association with Autism, ADHD, Dementia, and Parkinson’s Disease
The association between glyphosate and various neurological disorders like autism, ADHD, dementia, and Parkinson’s disease is closely linked to the gut microbiome, neurotransmitters, detoxification capacity, and inflammatory responses. While these diseases have complex causes, the hypothesis is being raised that glyphosate exposure could act as one environmental factor.
Commonly Proposed Mechanisms
Gut-Brain Axis Disruption:
- Gut Microbiome Alterations: Glyphosate can disrupt the balance of gut microbes, leading to ‘Leaky Gut Syndrome’ where intestinal barrier permeability increases due to a decrease in beneficial bacteria and an increase in harmful bacteria.
- Neurotransmitter Impact: Gut microbes produce various neurotransmitters and their precursors, such as serotonin and dopamine. If glyphosate inhibits the shikimate pathway in gut microbes, the availability of tryptophan (a serotonin precursor) may decrease.
- Inflammation and Toxin Influx: Through ‘Leaky Gut Syndrome,’ toxins or microbial metabolites entering the bloodstream can cause neuroinflammation, increasing the risk of neurological disorders.
Citation 2: Seneff, S., Swanson, N., & Li, C. (2015). Glyphosate impairs the shikimate pathway in bacteria, fungi, algae, and archaea. In Bioactive Food Peptides in Health and Disease (pp. 577-628). Academic Press. This paper extensively discusses how glyphosate disrupts the shikimate pathway in gut microbes, inhibiting the production of essential amino acids like tryptophan, and how this can be linked to neurological disorders.
Disease-Specific Associations
Autism (Autism Spectrum Disorder):
- Mechanism: Hypotheses link gut microbiome imbalance (especially an increase in Clostridium species), abnormal serotonin metabolism, and neuroinflammation to autism onset and symptom exacerbation. Reports suggest glyphosate can influence these mechanisms. For example, if gut microbes produce less tryptophan, serotonin synthesis may decrease, potentially affecting neurodevelopment.
Citation 3: Shaw, W. (2013). Evidence of glyphosate in autism. Journal of Toxicology and Environmental Health, Part B, 16(2), 79-91. Note: This paper was later retracted after academic controversy, but research on the association between autism and glyphosate continues. Notably, researchers like Seneff et al. are active in this field.
ADHD (Attention-Deficit/Hyperactivity Disorder):
- Mechanism: Imbalances in neurotransmitters like dopamine and norepinephrine, gut microbiome dysbiosis, and exposure to environmental toxins are known to be associated with ADHD development. Claims that glyphosate can affect these pathways continue to be raised. The potential for gut microbiome disruption to increase the risk of neurodevelopmental disorders is particularly noteworthy.
Dementia (Alzheimer’s Disease, etc.):
- Mechanism: Neuroinflammation, oxidative stress, mitochondrial dysfunction, and amyloid plaque/tau protein accumulation are known as key mechanisms of dementia. In this regard, initial research findings suggest that glyphosate may influence these factors. For instance, chronic oxidative stress can accelerate brain cell damage.
- Note: The hypothesis regarding amyloid plaque accumulation as a primary mechanism of dementia will be discussed in more detail in a separate section.
Parkinson’s Disease:
- Mechanism: Damage to dopaminergic neurons, abnormal accumulation of alpha-synuclein protein, mitochondrial dysfunction, and oxidative stress are linked to Parkinson’s disease. Some animal studies have also reported that glyphosate can induce dopaminergic neurotoxicity or cause mitochondrial damage. While various studies propose possibilities through different mechanisms, a clear causal relationship is not yet firmly established.
3. Academic Stance and Research Limitations
The association between neurological disorders and glyphosate is a highly active area of academic research. However, there are several limitations and debates.
Firstly, autism, ADHD, dementia, and Parkinson’s disease are multifactorial diseases resulting from a complex interplay of genetic, environmental, and lifestyle factors. Therefore, it is difficult to claim that glyphosate is the “sole cause” of these diseases.
Secondly, while some studies find an association with glyphosate, others report no association or even conflicting results. These differences can arise from variations in study design, exposure levels, target populations, and control of confounding variables.
Furthermore, Monsanto (now owned by Bayer) continues to advocate for the safety of glyphosate. They argue that despite decades of widespread use, scientific evidence of harm has not been clearly established. Nevertheless, the company has been involved in numerous lawsuits due to this product, paying substantial compensation, and new lawsuits continue to emerge.
How should we understand this? Bayer, well-known for Aspirin, took on an enormous burden by acquiring Monsanto. Yet, they continue to assert glyphosate’s harmlessness while simultaneously acquiring other agrochemical companies. This decision reveals not just a pharmaceutical company’s pursuit of profit, but also the structural problems of the industrial agricultural system. We will explore Bayer in more detail later.
Conclusion: The Ongoing Scientific Debate and Our Choices
The human health effects of glyphosate, particularly its association with neurological disorders, remain an ongoing scientific debate. Even though the shikimate pathway does not directly exist in humans, hypotheses consistently propose that it can disrupt the gut microbiome, affect detoxification capabilities, and induce oxidative stress.
How should we respond amid this uncertainty?
- Precautionary Principle: Even if scientific evidence is not 100% established, if a potential risk exists, measures should be taken to prevent harmful outcomes. This principle is especially important for children, pregnant women, individuals diagnosed with diseases or conditions, and those with weakened immunity.
- Critical Acceptance of Information: Rather than blindly accepting information from experts or media, it is essential to critically examine information from diverse sources and make your own judgments.
- Choosing Safe Foods: For foods with glyphosate residue concerns (e.g., imported wheat, corn, soybeans, lentils), choosing organic, Non-GMO, or glyphosate-free certified products whenever possible is a good way to reduce potential exposure. Prioritizing domestic produce and seasonal foods is also a wise approach.
- Continued Research and Policy Change Advocacy: Academia should actively pursue more in-depth and independent research, and governments should prioritize consumer safety by strengthening chemical regulations and food safety standards.
Just as Rachel Carson’s “Silent Spring” warned of the dangers of DDT, we have a responsibility to continuously question how modern chemicals like glyphosate affect our ‘silent organs’ and nervous system, and to seek better answers.
By the way, did you hear about a rather refreshing bill passed in the US this spring? It might be early summer or even midsummer depending on your location, but even if it’s an out-of-season spring story, its content is fresh enough that I hope to share it with you.
While curious about this out-of-season spring tale, you might enjoy re-reading Shakespeare’s “A Midsummer Night’s Dream.” Moreover, listening to Mendelssohn’s “A Midsummer Night’s Dream” can also deepen your curiosity. You could listen to the “Wedding March” and reminisce about past weddings or imagine future ones. These moments of leisure and dreaming, even trivial curiosities, contribute to mental and physical well-being.
Perhaps someone might say, “I’m already well aware of your warnings. Glyphosate and GM food ingredients have long disappeared from our dining table. Anyway, thanks for your concern. For others, maybe, but for me, this article feels like a waste of time. I have a golf appointment after walking my dog in the park, so I must excuse myself now.”
Next Preview: Hopefully, this article will reach you before you head out for a dog walk in the park, or before you leave for the golf course. The next article will continue with the theme, “An Unexpected Encounter with a Foe in the Park, or at the Golf Course?”
References
- Author: Mesnage, S., & Antoniou, M. N.
- Source: Food and Chemical Toxicology, 2017.
- Title: Ignoring the Obvious: The Scientific and Regulatory Non-Compliance of Glyphosate Risk Assessments.
- Summary: This review critically examines the limitations of existing regulatory frameworks for glyphosate toxicity assessment. It particularly points out that the toxic effects of other components (surfactants, etc.) included in glyphosate formulations are overlooked, and that research on long-term and complex exposure is insufficient. It emphasizes the need for evaluating the entire commercial formulation, not just glyphosate as a single substance.
- Author: Van Bruggen, A. H. C., He, M. M., Shin, K., Mai, V., Jeong, K. C., Finckh, M. R., & Gaskell, J. (2018).
- Source: Environmental Pollution, 2018.
- Title: Environmental and health effects of the herbicide glyphosate.
- Summary: This paper broadly reviews the environmental and health effects of glyphosate. It covers its impact on soil microorganisms and aquatic ecosystems, as well as its potential effects on the human gut microbiome, immune system, and nervous system. It suggests the possibility that glyphosate’s effects on microorganisms can serially influence human health through the food chain.
- Author: Rueda-Ruzafa, L., Cruz, F., Roman, P., & Cardona, D. (2019).
- Source: Environmental Research, 2019.
- Title: Gut microbiota and neurological diseases: A systematic review and meta-analysis.
- Summary: This systematic review and meta-analysis explore the association between gut microbiota and various neurological diseases (autism spectrum disorder, Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, etc.). While it does not directly address glyphosate, it supports the general principle that gut-brain axis disruption plays a crucial role in the development of neurological diseases, providing background knowledge for the hypothesis that glyphosate can affect the nervous system through gut microbiome disruption.
- Author: Mills, K., Niedzwiecki, A., & Rath, M. (2020).
- Source: Journal of Cellular and Molecular Medicine, 2020.
- Title: Review on the mechanisms of action of glyphosate in mammalian systems and its potential link to cancer and other diseases.
- Summary: This review details various mechanisms by which glyphosate acts in mammalian systems, particularly highlighting mitochondrial dysfunction, induction of oxidative stress, and the potential for (indirect) DNA damage. It comprehensively examines evidence linking glyphosate to various chronic diseases, including cancer, and emphasizes the need for additional independent research.
- Author: Li, C., Seneff, S., & Swanson, N. (2021).
- Source: Environmental Science and Pollution Research, 2021.
- Title: Glyphosate, aluminum, and fluoride: A trifecta of toxicity in neurological disease?
- Summary: This paper explores the hypothesis that glyphosate, along with other environmental toxins like aluminum and fluoride, may have synergistic effects on neurological diseases. It suggests that glyphosate’s ability to chelate (bind) metal ions and its impact on the microbiome can enhance neurotoxic pathways, emphasizing the importance of complex environmental exposures.
Japanese Translation
早期警告から遅れて学ぶ教訓：終わらない化学物質の論争、グリホサートと私たちの健康
前回の記事で説明した**「シキミ酸経路 (shikimate pathway)」**を覚えていますか？この経路は、植物が生存に不可欠な芳香族アミノ酸（トリプトファン、チロシン、フェニルアラニン）を合成するために使用されます。そして、グリホサートはこのシキミ酸経路を標的とします。
ある方からこのような質問をいただきました。「シキミ酸経路は人間に存在しないのに、グリホサートがどうして人体に有害だと関連付けられるのですか？」これはまさに「素晴らしい質問」だと思います。
今から、この質問に対する答えを詳しく解説していきます。
1. シキミ酸経路と人体への有害性：腸内微生物 (Gut Microbiome) が鍵！
まず、シキミ酸経路は植物と特定の微生物にのみ存在します。したがって、グリホサートが人間に直接有害であるという事実を理解するためには、私たちは自身の**「腸内微生物 (Gut Microbiome)」**に注目する必要があります。
私たちの腸内には無数の微生物が共生しており、その多くはシキミ酸経路を持っており、必須アミノ酸を合成しています。しかし、私たちがグリホサート残留物を含む食品、例えば輸入小麦粉やGM作物を餌にした畜肉を摂取すると、この化学物質は未消化のまま腸に到達します。
人間の腸内にいる様々な微生物（細菌、真菌など）は、植物と同様にシキミ酸経路を持っており、私たちに必要なアミノ酸（トリプトファン、チロシン、フェニルアラニン）を作り出しています。問題は、グリホサートがこの腸内微生物のシキミ酸経路に影響を与え、必須アミノ酸の合成を阻害する点です。これにより、有益な腸内微生物（例：ラクトバチルス菌、ビフィズス菌）の増殖が抑制される可能性があります。一方で、シキミ酸経路を持たないか、グリホサートに耐性を持つ有害菌（例：クロストリジウム・ボツリヌス菌、サルモネラ菌など）は、逆に増殖する可能性があります。
結果として、このような不均衡は**「腸内微生物叢異常症 (dysbiosis)」**を引き起こすことになります。そして、腸内微生物が作るトリプトファン、チロシン、フェニルアラニンは人間にとって非常に重要な栄養素です。特にトリプトファンは神経伝達物質であるセロトニンの前駆体であるため、微生物のシキミ酸経路が阻害されると、このアミノ酸の体内での利用可能性も減少する可能性があります。
さらに、一部の研究では、グリホサートが人間の肝臓にあるチトクロムP450（CYP）酵素システムを阻害する可能性があるとも主張されています。このCYP酵素は、体内の毒素、薬物、環境汚染物質などを解毒・代謝する上で非常に重要です。もしこの酵素システムが阻害されれば、私たちの体の毒素排出能力が低下し、毒素の蓄積が増加する可能性があります。
引用論文 1: Samsel, A., & Seneff, S. (2013). Glyphosate’s suppression of cytochrome P450 enzymes and amino acid biosynthesis by the gut microbiome: pathways to modern diseases. Interdisciplinary Toxicology, 6(4), 163-184. この論文は、グリホサートが腸内微生物のシキミ酸経路を抑制して必須アミノ酸の合成を妨げ、さらに人間のCYP酵素を抑制して解毒能力を低下させる可能性があると主張しています。そして、これにより自閉症、認知症などの様々な慢性疾患が発生する可能性があると論じています。
がん発生メカニズム（間接的関連性） グリホサートが直接的に人間の細胞DNAを損傷してがんを誘発するという明確なメカニズムは、まだ解明されていません。しかし、以下のような間接的なメカニズムががん発生と関連している可能性があるという仮説が継続的に提示されています。
私たちの体の腸内微生物叢の不均衡は、慢性炎症、免疫機能異常、毒素生成増加など、様々な形でがん発生リスクを高める可能性があります。健康な腸内環境は、発がん物質の吸収を減らし、免疫防御機能を強化する上で重要です。
また、一部の研究では、グリホサートが細胞内の酸化ストレスを増加させる可能性があると示唆されています。この酸化ストレスは、活性酸素が過剰に生成されて細胞を損傷する状態であり、DNA損傷につながり、がん発生リスクを高める可能性があります。もしCYP酵素抑制仮説が事実であれば、私たちの体の解毒能力が低下し、発がん物質が体内に長く留まることになります。このプロセスは、最終的に細胞損傷とがん発生リスクを高める結果をもたらす可能性があります。
さらに、腸内微生物の不均衡やその他のメカニズムによって免疫システムが撹乱されると、がん細胞を監視し排除する重要な免疫機能が弱まる可能性があります。
要約: グリホサートの発がん可能性（IARCグループ2A分類）は、直接的なDNA損傷ではなく、主に腸内微生物の乱れ、酸化ストレスの増加、解毒能力の低下、免疫システムの撹乱など、間接的なメカニズムで説明されています。これは依然として多くの研究が進行中の分野でもあります。
2. 自閉症、ADHD、認知症、パーキンソン病との関連性メカニズム
自閉症、ADHD、認知症、パーキンソン病など、様々な神経系疾患との関連性は、腸内微生物叢、神経伝達物質、解毒能力、炎症反応などと密接に結びついて説明されます。もちろん、これらの疾患は複合的な原因を持っていますが、グリホサートへの曝露が環境要因の一つとして作用する可能性があるという仮説が提唱されています。
共通して提案されるメカニズム
腸脳軸の乱れ (Gut-Brain Axis Disruption):
- 腸内微生物の変化: グリホサートが腸内微生物のバランスを崩すと、善玉菌の減少と悪玉菌の増加により、腸壁の透過性が高まる**「リーキーガット症候群 (Leaky Gut Syndrome)」**が発生する可能性があります。
- 神経伝達物質への影響: 腸内微生物は、セロトニン、ドーパミンなど、様々な神経伝達物質とその前駆体を生成します。グリホサートが腸内微生物のシキミ酸経路を抑制すると、トリプトファン（セロトニン前駆体）の利用可能性が減少する可能性があります。
- 炎症および毒素の流入: 「リーキーガット症候群」を通じて毒素や微生物の代謝産物が血流に流入すると、脳の炎症 (neuroinflammation) を引き起こし、神経系疾患のリスクを高める可能性があります。
引用論文 2: Seneff, S., Swanson, N., & Li, C. (2015). Glyphosate impairs the shikimate pathway in bacteria, fungi, algae, and archaea. In Bioactive Food Peptides in Health and Disease (pp. 577-628). Academic Press. この論文は、グリホサートが腸内微生物のシキミ酸経路を阻害し、トリプトファンなどの必須アミノ酸の生成を妨げ、これが神経系疾患と関連しうることを深く掘り下げています。
各疾患別の関連性
自閉症 (自閉スペクトラム症):
- メカニズム: 腸内微生物の不均衡（特にクロストリジウム属細菌の増加）、異常なセロトニン代謝、脳の炎症などが自閉症の発症や症状悪化に関連するという仮説があります。また、グリホサートがこれらのメカニズムに影響を与える可能性があるという報告があります。例えば、腸内微生物がトリプトファンを少なく生成すると、セロトニン合成が減少し、これが神経発達に影響を与える可能性があります。
引用論文 3: Shaw, W. (2013). Evidence of glyphosate in autism. Journal of Toxicology and Environmental Health, Part B, 16(2), 79-91. 注：この論文は学術的な論争の末に撤回されましたが、自閉症とグリホサートの関連性に関する研究は依然として続いています。特にSeneffらの研究者はこの分野で活発に活動しています。
ADHD (注意欠陥・多動性障害):
- メカニズム: ドーパミンやノルエピネフリンなどの神経伝達物質の不均衡、腸内微生物叢の異常、環境毒素への曝露などがADHDの発症に関連すると知られています。また、グリホサートがこれらの経路に影響を与える可能性があるという主張も継続的に提起されています。特に、腸内微生物の乱れが神経発達障害のリスクを高める可能性がある点が注目されています。
認知症 (アルツハイマー病など):
- メカニズム: 脳の炎症、酸化ストレス、ミトコンドリア機能異常、アミロイド斑およびタウタンパク質の蓄積などが認知症の主要なメカニズムとして知られています。これに関連して、グリホサートがこれらの要因に影響を与える可能性があるという初期の研究結果が報告されています。例えば、酸化ストレスが慢性化すると、脳細胞の損傷が加速する可能性があります。
- 注：アミロイド斑の蓄積が認知症の主要なメカニズムであるという仮説については、別途の章でさらに深く掘り下げる予定です。
パーキンソン病:
- メカニズム: ドーパミン作動性神経細胞の損傷、アルファ・シヌクレインタンパク質の異常な蓄積、ミトコンドリア機能異常、酸化ストレスなどがパーキンソン病に関連します。また、グリホサートがドーパミン神経細胞毒性を誘発したり、ミトコンドリアに損傷を与える可能性があるという動物実験の結果も一部発表されています。このように、複数の研究が異なるメカニズムを通じて可能性を提示していますが、まだ明確に確立された因果関係とは見なされていません。
3. 学界の立場と研究の限界
神経系疾患とグリホサートの関連性は、現在学界で非常に活発に研究されている分野です。しかし、いくつかの限界点と論争も存在します。
まず、自閉症、ADHD、認知症、パーキンソン病などは、遺伝的要因、環境要因、生活習慣など、様々な要素が複合的に作用する多因子性疾患です。したがって、グリホサートがこれらの疾患の「単独原因」であると主張することは困難です。
次に、一部の研究ではグリホサートとの関連性を見出していますが、他の研究では関連性が見つからなかったり、あるいは矛盾する結果を報告したりすることもあります。これらの違いは、研究デザイン、曝露量、対象集団、交絡因子の制御の違いに起因する可能性があります。
さらに、モンサント（現在はバイエル所有）側は、グリホサートの安全性を継続的に擁護しています。彼らは、この製品が数十年にわたり広範囲に使用されてきたにもかかわらず、科学的に有害性が明確に証明されていないと主張しています。それにもかかわらず、同社はこの製品のために数多くの訴訟に巻き込まれ、巨額の賠償金を支払っており、依然として新たな訴訟が続いています。
この部分をどのように理解すればよいでしょうか？ アスピリンでよく知られているバイエルは、モンサントを買収することで巨大な負担を背負いました。しかし、彼らは依然としてグリホサートの無害性を主張し、同時に他の農薬・除草剤企業までも買収するという戦略を選択しました。このような決定は、単に製薬会社の利益追求にとどまらず、産業農業システムの構造的な問題を表す事例でもあります。バイエル社についても、後日さらに詳しく見ていく予定です。
結論：終わらない科学的論争と私たちの選択
グリホサートの人体への有害性、特に神経系疾患との関連性は、依然として進行中の科学的論争です。たとえシキミ酸経路が人間に直接存在しなくとも、腸内微生物叢を乱し、解毒能力に影響を与え、酸化ストレスを誘発する可能性があるという仮説が継続的に提示されています。
このような不確実性の中で、私たちはどのように対応すべきでしょうか？
- 予防原則 (Precautionary Principle): 科学的な証拠が100%確立されていなくても、潜在的なリスクがあるならば、それを予防するための措置を講じるべきであるという原則です。特に子供や妊婦、特定の疾患や病状と診断された方、免疫力が脆弱な人々には、より重要に適用されるべきです。
- 情報の批判的受容: 専門家やメディアの情報を盲目的に受け入れるのではなく、様々な情報源を批判的に検討し、自ら判断する努力が必要です。
- 安全な食品の選択: グリホサート残留の懸念がある食品（輸入小麦、トウモロコシ、大豆、レンズ豆など）については、可能な限り有機栽培、非GM、またはグリホサートフリー認証製品を選ぶことが、潜在的な曝露を減らす良い方法です。そして、私たちの国産農産物や旬の食品を優先的に選ぶことも賢明な方法です。
- 継続的な研究と政策変更の促進: 学界では、より深く独立した研究が活発に進められるべきであり、政府は消費者の安全を最優先とし、化学物質の規制および食品安全基準を強化すべきです。
レイチェル・カーソンの『沈黙の春』がDDTの危険性を警告したように、私たちはグリホサートのような現代の化学物質が、私たちの**「沈黙の臓器」**と神経系にどのような影響を与えるのかについて絶えず問いかけ、より良い答えを見つける責任があります。
そういえば、この春、アメリカで少々春らしい法案が可決されたというニュースをご存知ですか？地域によっては初夏、あるいは真夏かもしれませんが、季節外れの春の話でも、その内容が久しぶりに新鮮なので、皆さんと分かち合いたいと思います。
季節外れの春の物語に興味を持ちながら、シェイクスピアの「真夏の夜の夢」を再び読み返してみるのも良いでしょう。加えて、メンデルスゾーンが作曲した「真夏の夜の夢」を鑑賞しながら好奇心を高めるのも良いですね。「結婚行進曲」を聴きながら昔の結婚生活を思い出したり、未来の結婚式を想像してみるのも良いでしょう。このようなゆったりとした気持ちや夢見ることのできる瞬間、そして些細な好奇心さえも心身の健康に役立ちます。
もしかしたら、こんなことを言う人もいるかもしれませんね。「あなたの警告はもう十分知っています。グリホサートやGM作物関連の食材なんて、我が家の食卓からとっくに消えています。とにかく心配してくれてありがとう。他の人はともかく、私にはこんな記事は時間の無駄に感じますね。犬と公園を散歩した後、ゴルフの約束があるので、これで失礼します。」
次回予告: できれば、犬と公園に散歩に出かける前、あるいはゴルフ場へ向かう前に、この記事が届くことを願っています。次回の記事は「公園で、ゴルフ場で、まさかの仇敵と遭遇？」をテーマに続きます。
参考文献
- 著者: Mesnage, S., & Antoniou, M. N.
- 出典: Food and Chemical Toxicology, 2017.
- タイトル: Ignoring the Obvious: The Scientific and Regulatory Non-Compliance of Glyphosate Risk Assessments.
- 内容要約: このレビュー論文は、グリホサートの毒性評価における既存の規制枠組みの限界を批判的に検証しています。特に、グリホサート製剤に含まれる他の成分（界面活性剤など）の毒性効果が見過ごされていることや、長期的かつ複合的な曝露に関する研究が不足していることを指摘しています。グリホサート単一物質ではなく、市販されている製剤全体に対する評価が必要であることを強調しています。
- 著者: Van Bruggen, A. H. C., He, M. M., Shin, K., Mai, V., Jeong, K. C., Finckh, M. R., & Gaskell, J. (2018).
- 出典: Environmental Pollution, 2018.
- タイトル: Environmental and health effects of the herbicide glyphosate.
- 内容要約: この論文は、グリホサートの環境および健康への影響を広範囲にわたってレビューしています。特に、土壌微生物、水生生態系への影響に加え、人間の腸内微生物、免疫システム、神経系に対する潜在的な影響を扱っています。グリホサートが微生物に与える影響が、食物連鎖を通じて人間の健康にまで連鎖的に影響を及ぼす可能性を提示しています。
- 著者: Rueda-Ruzafa, L., Cruz, F., Roman, P., & Cardona, D. (2019).
- 出典: Environmental Research, 2019.
- タイトル: Gut microbiota and neurological diseases: A systematic review and meta-analysis.
- 内容要約: この系統的レビューおよびメタアナリシスは、腸内微生物と様々な神経系疾患（自閉スペクトラム症、パーキンソン病、アルツハイマー病、多発性硬化症など）との関連性を探求しています。グリホサートを直接扱ってはいませんが、腸脳軸の乱れが神経系疾患の発症に重要な役割を果たすという一般的な原則を裏付け、グリホサートが腸内微生物の乱れを通じて神経系に影響を与える可能性があるという仮説の背景知識を提供しています。
- 著者: Mills, K., Niedzwiecki, A., & Rath, M. (2020).
- 出典: Journal of Cellular and Molecular Medicine, 2020.
- タイトル: Review on the mechanisms of action of glyphosate in mammalian systems and its potential link to cancer and other diseases.
- 内容要約: このレビューは、グリホサートが哺乳類システムで作用する複数のメカニズムを詳細に説明しており、特にミトコンドリア機能不全、酸化ストレス誘発、DNA損傷（間接的）の可能性などを強調しています。また、グリホサートががんを含む様々な慢性疾患と関連しうるという証拠を総合的に検討し、追加的な独立した研究の必要性を強く訴えています。
- 著者: Li, C., Seneff, S., & Swanson, N. (2021).
- 出典: Environmental Science and Pollution Research, 2021.
- タイトル: Glyphosate, aluminum, and fluoride: A trifecta of toxicity in neurological disease?
- 内容要約: この論文は、グリホサートがアルミニウムやフッ化物のような他の環境毒素と組み合わさることで、神経系疾患に対して相乗効果をもたらす可能性があるという仮説を探求しています。特に、グリホサートが金属イオンをキレート（結合）する能力と、マイクロバイオームに与える影響を通じて神経毒性経路が強化されうることを示唆し、複合的な環境曝露の重要性を強調しています。
Deep Research
Canvas
Shikimate Pathway: A pathway that commands the synthesis of amino acids necessary for survival?
Do you remember the ‘shikimate pathway’ that we explained in the last article? This pathway is used by plants to synthesize essential aromatic amino acids (tryptophan, tyrosine, phenylalanine) necessary for their survival. And glyphosate precisely targets this shikimate pathway. This led to a question: “If the shikimate pathway doesn’t exist in humans, then how is glyphosate related to human health hazards?” I think this is truly a ‘great question’. From now on, I will thoroughly answer this question.
1. Shikimate Pathway and Human Health Hazards: The Gut Microbiome is Key!
The shikimate pathway exists only in plants and certain microorganisms. Therefore, to understand how glyphosate is directly harmful to humans, we need to focus on our ‘gut microbiome’. Our gut contains countless microorganisms in symbiosis, many of which, like plants, possess the shikimate pathway and produce essential amino acids.
Mechanisms by which Glyphosate Harms the Human Body
Glyphosate Ingestion into the Gut: When we consume food with glyphosate residue, such as imported wheat flour or meat from animals fed GM crops, glyphosate enters the intestines undigested.
Targeting Gut Microbes: Our human gut contains a diverse array of microorganisms (bacteria, fungi, etc.) living in symbiosis. Many of these microbes, like plants, possess the shikimate pathway to synthesize essential amino acids (tryptophan, tyrosine, phenylalanine) that are vital for us.
Gut Microbiome Disruption: The problem is that glyphosate directly impacts the shikimate pathway of these gut microorganisms, hindering the synthesis of essential amino acids. This can suppress the growth of beneficial gut microbes (e.g., Lactobacillus, Bifidobacterium).
Decrease in Beneficial Bacteria and Increase in Harmful Bacteria: Simultaneously, harmful bacteria that lack the shikimate pathway or are resistant to glyphosate (e.g., Clostridium botulinum, Salmonella, etc.) can proliferate. Consequently, this imbalance leads to ‘gut dysbiosis’.
Decrease in Essential Amino Acids: Tryptophan, tyrosine, and phenylalanine produced by gut microbes are very important nutrients for humans. Especially, tryptophan is a precursor to the neurotransmitter serotonin. Therefore, if the microbial shikimate pathway is inhibited, the bioavailability of these amino acids in the body can decrease.
Cytochrome P450 Enzyme Inhibition (Additional Mechanism): Some studies also claim that glyphosate can inhibit the cytochrome P450 (CYP) enzyme system in the human liver. This CYP enzyme is crucial for detoxifying and metabolizing various toxins, drugs, and environmental pollutants in the body. If this enzyme system is inhibited, our body’s detoxification capacity can decrease, leading to an increased accumulation of toxins.
Cited Paper 1: Samsel, A., & Seneff, S. (2013). Glyphosate’s suppression of cytochrome P450 enzymes and amino acid biosynthesis by the gut microbiome: pathways to modern diseases. Interdisciplinary Toxicology, 6(4), 163-184. This paper argues that glyphosate can inhibit the shikimate pathway of gut microbes, thereby hindering essential amino acid synthesis, and further suppress human CYP enzymes, leading to a reduction in detoxification capabilities. It also suggests that this can contribute to various chronic diseases such as autism and dementia.
Cancer Development Mechanisms (Indirect Association)
A clear mechanism by which glyphosate directly damages human cellular DNA and causes cancer has not yet been elucidated. However, the following indirect mechanisms have been proposed as possibly related to cancer development.
Gut Microbiome Imbalance: Imbalance in the gut microbiome can increase the risk of cancer through various mechanisms, including chronic inflammation, immune dysfunction, and increased toxin production. A healthy gut environment is crucial for reducing carcinogen absorption and enhancing immune defense.
Indirect Induction of Oxidative Stress and DNA Damage: Some studies suggest that glyphosate can increase intracellular oxidative stress. Oxidative stress is a condition where excessive reactive oxygen species are produced, damaging cells, and potentially leading to DNA damage, thus increasing cancer risk.
Decreased Detoxification Capacity: If the CYP enzyme inhibition hypothesis is true, our body’s detoxification capacity would decrease, allowing carcinogens to remain in the body for longer. This could ultimately lead to cell damage and an increased risk of cancer.
Immune System Disruption: If the immune system is disrupted through gut microbiome imbalance and other mechanisms, crucial immune functions for monitoring and eliminating cancer cells may be weakened.
Summary: The carcinogenic potential of glyphosate (IARC Group 2A classification) is explained primarily through indirect mechanisms such as gut microbiome disruption, increased oxidative stress, decreased detoxification capacity, and immune system disruption, rather than direct DNA damage. This is still an active area of research.
2. Association Mechanisms with Autism, ADHD, Dementia, and Parkinson’s Disease
The association of glyphosate with various neurological diseases such as autism spectrum disorder (ASD), ADHD (Attention Deficit Hyperactivity Disorder), dementia, and Parkinson’s disease is also closely linked to the gut microbiome, neurotransmitters, detoxification capacity, and inflammatory responses. While these diseases have complex causes, the hypothesis that glyphosate exposure can act as an environmental factor continues to be raised.
Commonly Proposed Mechanisms
Gut-Brain Axis Disruption:
Changes in Gut Microbiota: If glyphosate disrupts the balance of gut microbes, a ‘leaky gut syndrome’ can occur, where increased intestinal permeability leads to a decrease in beneficial bacteria and an increase in harmful bacteria. This syndrome can be a cause of various problems.
Impact on Neurotransmitters: Gut microbes produce various neurotransmitters and their precursors, such as serotonin and dopamine. If glyphosate inhibits the shikimate pathway of gut microbes, the availability of tryptophan (a precursor to serotonin) can decrease. This reduction in tryptophan can directly affect mood regulation, cognitive function, and motor skills.
Inflammation and Toxin Influx: Through ‘leaky gut syndrome’, toxins or microbial metabolites can enter the bloodstream, causing neuroinflammation and increasing the risk of neurological diseases.
Cited Paper 2: Seneff, S., Swanson, N., N., & Li, C. (2015). Glyphosate impairs the shikimate pathway in bacteria, fungi, algae, and archaea. In Bioactive Food Peptides in Health and Disease (pp. 577-628). Academic Press. This paper delves into how glyphosate disrupts the shikimate pathway in gut microbes, hindering the production of essential amino acids like tryptophan, and thereby linking it to neurological diseases. It is a significant study that proposes hypotheses linking glyphosate to autism and dementia.
Decreased Detoxification Capacity: As mentioned earlier, the hypothesis that glyphosate inhibits CYP enzymes suggests that it can impede the detoxification and excretion of other toxins or drugs entering the body. This can lead to the accumulation of neurotoxic substances, which can damage brain cells and contribute to the development of neurological diseases.
Mitochondrial Dysfunction: Some studies suggest that glyphosate can cause dysfunction in mitochondria, the energy production factories of cells. Mitochondrial dysfunction is a well-known major cause of neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease.
Association with Specific Diseases (Research Stage)
Autism (Autism Spectrum Disorder):
Mechanism: Hypotheses link gut microbiome imbalance (particularly an increase in Clostridium species), abnormal serotonin metabolism, and brain inflammation to the onset and worsening of autism symptoms. There are reports that glyphosate can influence these mechanisms.
Cited Paper 3: Shaw, W. (2013). Evidence of glyphosate in autism. Journal of Toxicology and Environmental Health, Part B, 16(2), 79-91. Note: While the Shaw paper mentioned above was retracted after academic controversy, research into the link between autism and glyphosate continues. Notably, researchers like Seneff are active in this field.
ADHD (Attention Deficit Hyperactivity Disorder):
Mechanism: Imbalance of neurotransmitters like dopamine and norepinephrine, gut microbiome dysbiosis, and exposure to environmental toxins are associated with ADHD. Claims that glyphosate can affect these pathways have also been made.
Dementia (e.g., Alzheimer’s Disease):
Mechanism: Brain inflammation, oxidative stress, mitochondrial dysfunction, and the accumulation of amyloid plaques and tau proteins are major mechanisms in dementia. Initial research results suggest that glyphosate can influence these factors. Note: The hypothesis that amyloid plaque accumulation is a major mechanism in dementia will be discussed in more detail in a separate section.
Parkinson’s Disease:
Mechanism: Damage to dopaminergic neurons, abnormal accumulation of alpha-synuclein protein, mitochondrial dysfunction, and oxidative stress are associated with Parkinson’s disease. Animal studies have reported that glyphosate can induce dopaminergic neurotoxicity or cause mitochondrial damage.
3. Academic Stance and Research Limitations
The association between neurological diseases and glyphosate is currently a very active area of research in academia. However, there are also some limitations and controversies.
Multifactorial Diseases: Autism, ADHD, dementia, Parkinson’s disease, etc., are multifactorial diseases resulting from a complex interplay of genetic factors, environmental factors, and lifestyle. Therefore, it is difficult to claim that glyphosate is the ‘sole cause’ of these diseases.
Conflicting Results: While some studies find an association with glyphosate, others do not, or even report conflicting results. Such differences can arise from variations in study design, exposure levels, target populations, and control for confounding variables.
Counterarguments from Bayer/Monsanto: Monsanto (now owned by Bayer) continues to advocate for the safety of glyphosate. They argue that despite the product being widely used for decades, its harmfulness has not been clearly scientifically proven. How should we understand their claim, given that they have already paid substantial compensation in lawsuits related to glyphosate and are still embroiled in continuous litigation?
Bayer, a giant pharmaceutical company that acquired the infamous Monsanto and is incurring financial losses due to glyphosate developed by Monsanto, yet continues to assert glyphosate’s safety and even acquires other agrochemical companies besides Monsanto.
Bayer, which gave birth to aspirin, represented by a white, round tablet with a cross mark. We will have time to discuss Bayer in more detail later.
Conclusion: The Unending Scientific Debate and Our Choices
The discussion on glyphosate’s human health hazards, particularly its association with neurological diseases, remains an ongoing scientific debate. Even though the shikimate pathway does not exist directly in humans, indirect associations with various diseases, including cancer, are consistently proposed through hypotheses that it can disrupt the gut microbiome, affect detoxification capacity, and induce oxidative stress.
How should we respond amidst this uncertainty?
Precautionary Principle: This principle states that even if scientific evidence is not 100% established, if there is a potential risk, measures should be taken to prevent it. This is especially important for children, pregnant women, and immunocompromised individuals.
Critical Acceptance of Information: Rather than blindly accepting information from experts or the media, it is necessary to critically examine information from various sources and make your own judgments. This is the stance of an informed consumer.
Choosing Safe Foods: For foods with concerns about glyphosate residue (e.g., imported wheat, corn, soybeans, lentils, and other beans), choosing organic, Non-GMO, or glyphosate-free certified products can be a good way to reduce potential exposure. Prioritizing domestic agricultural products and seasonal foods is also a wise choice.
Promoting Continuous Research and Policy Change: Academia needs to conduct more in-depth and independent research, and governments should prioritize consumer safety by further strengthening chemical regulations and food safety standards.
Just as Rachel Carson’s Silent Spring warned of the dangers of DDT, we have a responsibility to continually ask questions about how modern chemicals like glyphosate affect our ‘silent organs’ and nervous system, and to seek better answers.
Did you happen to hear about a bill that passed this spring in the US, bringing a bit of spring air? If not, I will arrange a chapter to share this somewhat belated spring news, perhaps in early summer or mid-summer depending on the region.
What kind of story will it be? You might want to re-read Shakespeare’s “A Midsummer Night’s Dream” or listen to Mendelssohn’s “A Midsummer Night’s Dream” to pique your curiosity.
Listening to “Wedding March” and reminiscing about past wedding days, or dreaming of a happy “Wedding March” in a bustling future, such moments of leisure and happy dreams can also contribute to a healthy mind and body.
Perhaps some might say, “I’m already well aware of your warnings. Glyphosate and GM-related ingredients have long disappeared from our dining table. Anyway, thanks for your concern. For others, maybe, but for me, this kind of article feels like a waste of time. I have a golf appointment after walking my dog in the park, so I’ll take my leave.”
Next Episode Preview: Hoping to deliver it before you walk your dog in the park or head to the golf course, the next article will inevitably(?) continue with the story of “An Unexpected Encounter with an Enemy at the Park or Golf Course.”
References
Author: Mesnage, S., & Antoniou, M. N. Source: Food and Chemical Toxicology, 2017. Title: Ignoring the Obvious: The Scientific and Regulatory Non-Compliance of Glyphosate Risk Assessments. Summary: This review critically examines the limitations of existing regulatory frameworks for glyphosate toxicity assessment. It particularly points out that the toxic effects of other ingredients (e.g., surfactants) in glyphosate formulations are overlooked, and there is a lack of research on long-term and complex exposure. It emphasizes the need for evaluating commercial formulations of glyphosate as a whole, rather than just the single substance.
Author: Van Bruggen, A. H. C., He, M. M., Shin, K., Mai, V., Jeong, K. C., Finckh, M. R., & Gaskell, J. (2018). Source: Environmental Pollution, 2018. Title: Environmental and health effects of the herbicide glyphosate. Summary: This paper extensively reviews the environmental and health effects of glyphosate. It covers its impact on soil microbes and aquatic ecosystems, as well as its potential effects on the human gut microbiome, immune system, and nervous system. It suggests the possibility that the effects of glyphosate on microorganisms can cascade through the food chain to impact human health.
Author: Rueda-Ruzafa, L., Cruz, F., Roman, P., & Cardona, D. (2019). Source: Environmental Research, 2019. Title: Gut microbiota and neurological diseases: A systematic review and meta-analysis. Summary: This systematic review and meta-analysis explore the association between gut microbiota and various neurological diseases (autism spectrum disorder, Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, etc.). While it does not directly address glyphosate, it supports the general principle that gut-brain axis disruption plays a crucial role in the development of neurological diseases, providing background knowledge for the hypothesis that glyphosate can affect the nervous system through gut microbiome disruption.
Author: Mills, K., Niedzwiecki, A., & Rath, M. (2020). Source: Journal of Cellular and Molecular Medicine, 2020. Title: Review on the mechanisms of action of glyphosate in mammalian systems and its potential link to cancer and other diseases. Summary: This review details several mechanisms by which glyphosate acts in mammalian systems, particularly emphasizing mitochondrial dysfunction, induction of oxidative stress, and potential (indirect) DNA damage. It also comprehensively reviews evidence suggesting that glyphosate can be linked to various chronic diseases, including cancer, and stresses the need for further independent research.
Author: Li, C., Seneff, S., & Swanson, N. (2021). Source: Environmental Science and Pollution Research, 2021. Title: Glyphosate, aluminum, and fluoride: A trifecta of toxicity in neurological disease? Summary: This paper explores the hypothesis that glyphosate can have synergistic effects on neurological diseases when combined with other environmental toxins like aluminum and fluoride. It suggests that glyphosate’s ability to chelate metal ions and its effects on the microbiome can enhance neurotoxic pathways, emphasizing the importance of complex environmental exposure.
日本語
シキミ酸経路：生存に必要なアミノ酸を合成するように命令する経路？
前回の記事で説明した**「シキミ酸経路（shikimate pathway）」**を覚えていますか？この経路は、植物が生存に必須な芳香族アミノ酸（トリプトファン、チロシン、フェニルアラニン）を合成する際に使用されます。そして、グリホサートはまさにこのシキミ酸経路を標的とします。これに対し、このような質問を受けました。「では、シキミ酸経路は人間には存在しないのに、グリホサートがどうして人体に有害性があるというのですか？」これはまさに「偉大な質問」だと思います。これから、この質問に対する答えを詳しく説明していきます。
1. シキミ酸経路と人体への有害性：腸内マイクロバイオーム（Gut Microbiome）が鍵！
シキミ酸経路は植物と特定の微生物にのみ存在します。したがって、グリホサートが人間に直接有害であるという事実を理解するには、まさに私たちの**「腸内マイクロバイオーム（Gut Microbiome）」**に注目する必要があります。私たちの腸の中には無数の微生物が共生しており、その多くは植物のようにシキミ酸経路を持っており、必須アミノ酸を作り出しています。
グリホサートが人体に害を及ぼすメカニズム
グリホサートの腸内流入： 私たちがグリホサートが残留している食品、例えば輸入小麦粉やGM作物を餌にした肉類を摂取すると、グリホサートは未消化のまま腸に入ってきます。
腸内微生物の標的： 人間の腸の中には、様々な微生物（細菌、真菌など）が共生しています。これらの微生物の多くは、植物のようにシキミ酸経路を持っており、私たちに不可欠なアミノ酸（トリプトファン、チロシン、フェニルアラニン）を合成しています。
腸内微生物の攪乱： 問題は、グリホサートがまさにこの腸内微生物のシキミ酸経路に影響を与え、必須アミノ酸の合成を阻害する点です。これにより、有益な腸内微生物（例：ラクトバチルス、ビフィドバクテリウム）の増殖が抑制される可能性があります。
善玉菌の減少と悪玉菌の増加： 同時に、シキミ酸経路を持たない、あるいはグリホサートに耐性のある有害な菌（例：クロストリジウム・ボツリヌム、サルモネラなど）は、かえって増殖する可能性があります。結果として、このような不均衡は**「腸内マイクロバイオーム異常症（dysbiosis）」**を引き起こします。
必須アミノ酸の減少： 腸内微生物が作り出すトリプトファン、チロシン、フェニルアラニンは、人間にとっても非常に重要な栄養素です。特にトリプトファンは神経伝達物質であるセロトニンの前駆体であるため、微生物のシキミ酸経路が抑制されると、これらのアミノ酸の体内での利用可能性も減少する可能性があります。
シトクロムP450酵素阻害（追加メカニズム）： 一部の研究では、グリホサートが人間の肝臓にあるシトクロムP450（CYP）酵素システムを阻害する可能性があるとも主張しています。このCYP酵素は、体内の毒素、薬物、環境汚染物質などを解毒し代謝する上で非常に重要です。もしこの酵素システムが阻害されれば、私たちの体の毒素排出能力が低下し、毒素の蓄積が増加する可能性があります。
引用論文1： Samsel, A., & Seneff, S. (2013). Glyphosate’s suppression of cytochrome P450 enzymes and amino acid biosynthesis by the gut microbiome: pathways to modern diseases. Interdisciplinary Toxicology, 6(4), 163-184. この論文は、グリホサートが腸内微生物のシキミ酸経路を抑制して必須アミノ酸の合成を妨げ、さらに人間のCYP酵素を抑制して解毒能力を低下させる可能性があると主張しています。そして、これにより自閉症や認知症など、様々な慢性疾患が発生する可能性があると述べています。
がん発生メカニズム（間接的関連性）
グリホサートが直接的に人間の細胞のDNAを損傷してがんを引き起こすという明確なメカニズムはまだ解明されていません。しかし、以下のような間接的なメカニズムががん発生と関連する可能性があるという仮説が提示されています。
腸内微生物の不均衡： 腸内マイクロバイオームの不均衡は、慢性炎症、免疫機能異常、毒素生成の増加など、様々な方法でがん発生リスクを高める可能性があります。健康な腸内環境は、発がん物質の吸収を減らし、免疫防御機能を強化する上で重要です。
酸化ストレスおよびDNA損傷の間接的な誘発： 一部の研究では、グリホサートが細胞内の酸化ストレスを増加させる可能性があると示唆しています。この酸化ストレスは、活性酸素が過剰に生成されて細胞を損傷する状態であり、DNA損傷につながることでがん発生リスクを高める可能性があります。
解毒能力の低下： もしCYP酵素阻害仮説が事実であれば、私たちの体の解毒能力が低下し、発がん物質が体内に長く留まることになります。これは最終的に細胞損傷とがん発生リスクを高める結果を招く可能性があります。
免疫システムの攪乱： 腸内微生物の不均衡やその他のメカニズムを通じて免疫システムが攪乱されると、がん細胞を監視し除去する重要な免疫機能が弱まる可能性があります。
要約： グリホサートの発がん可能性（IARCグループ2A分類）は、直接的なDNA損傷よりも、主に腸内微生物の攪乱、酸化ストレスの増加、解毒能力の低下、免疫システムの攪乱といった間接的なメカニズムを通じて説明されています。これは依然として多くの研究が進められている分野でもあります。
2. 自閉症、ADHD、認知症、パーキンソン病との関連性メカニズム
自閉症（自閉スペクトラム症）、ADHD（注意欠陥多動性障害）、認知症、パーキンソン病など、様々な神経系疾患との関連性もまた、腸内マイクロバイオーム、神経伝達物質、解毒能力、炎症反応などと密接に結びついて説明されています。もちろん、これらの疾患は複合的な原因を持っていますが、グリホサート曝露が環境要因の一つとして作用する可能性があるという仮説が継続的に提起されています。
共通して提案されるメカニズム
腸脳軸の攪乱（Gut-Brain Axis Disruption）：
腸内微生物の変化： グリホサートが腸内微生物のバランスを崩すと、善玉菌の減少と悪玉菌の増加により、腸壁の透過性が高まる**「リーキーガット症候群（Leaky Gut Syndrome）」**が発生する可能性があります。この症候群は様々な問題の原因となります。
神経伝達物質への影響： 腸内微生物はセロトニン、ドーパミンなど様々な神経伝達物質とその前駆体を生成します。グリホサートが腸内微生物のシキミ酸経路を抑制すると、トリプトファン（セロトニンの前駆体）の利用可能性が減少する可能性があります。このトリプトファンの減少は、気分調整、認知機能、運動能力などに直接的な影響を与える可能性があります。
炎症および毒素の流入： 「リーキーガット症候群」を通じて毒素や微生物の代謝産物が血流に流入すると、これは**脳炎症（neuroinflammation）**を引き起こし、神経系疾患の発生リスクを高める可能性があります。
引用論文2： Seneff, S., Swanson, N., & Li, C. (2015). Glyphosate impairs the shikimate pathway in bacteria, fungi, algae, and archaea. In Bioactive Food Peptides in Health and Disease (pp. 577-628). Academic Press. この論文は、グリホサートが腸内微生物のシキミ酸経路を攪乱し、トリプトファンなどの必須アミノ酸の生成を阻害することで、神経系疾患と関連する可能性を深く掘り下げています。特に、自閉症、認知症などとの関連性仮説を提示する重要な研究です。
毒素解毒能力の低下： 前述したように、グリホサートがCYP酵素を阻害するという仮説は、体内に入ってくる他の毒素や薬物の解毒および排出を妨げる可能性があります。これは神経毒性物質の蓄積を引き起こす可能性があり、このような神経毒性物質は脳細胞を損傷し、神経系疾患の発症に寄与する可能性があります。
ミトコンドリア機能異常： 一部の研究では、グリホサートが細胞のエネルギー生産工場であるミトコンドリアの機能に異常をもたらす可能性があると提案しています。ミトコンドリア機能異常は、パーキンソン病、アルツハイマー病などの神経変性疾患の主要な原因の一つとしてよく知られています。
各疾患との関連性（研究段階）
自閉症（自閉スペクトラム症）：
メカニズム： 腸内微生物の不均衡（特にクロストリジウム属細菌の増加）、異常なセロトニン代謝、脳炎症などが自閉症の発症および症状悪化と関連するという仮説があります。グリホサートはこれらのメカニズムに影響を与える可能性があるという報告があります。
引用論文3： Shaw, W. (2013). Evidence of glyphosate in autism. Journal of Toxicology and Environmental Health, Part B, 16(2), 79-91. 補足：上記Shawの論文は学術的な議論の末に撤回されましたが、自閉症とグリホサートの関連性に関する研究は継続して行われています。特にSeneffらの研究陣がこの分野で活発に活動しています。
ADHD（注意欠陥多動性障害）：
メカニズム： ドーパミン、ノルエピネフリンなどの神経伝達物質の不均衡、腸内マイクロバイオームの異常、そして環境毒素への曝露などがADHDと関連しています。グリホサートがこれらの経路に影響を与える可能性があるという主張も提示されています。
認知症（アルツハイマー病など）：
メカニズム： 脳炎症、酸化ストレス、ミトコンドリア機能異常、そしてアミロイドプラークおよびタウタンパク質の蓄積などが認知症の主要なメカニズムです。グリホサートがこれらの要因に影響を与える可能性があるという初期の研究結果が報告されています。 補足：アミロイドプラークの蓄積が認知症の主要なメカニズムであるという仮説については、別途の章でさらに深く掘り下げる予定です。
パーキンソン病：
メカニズム： ドーパミン作動性神経細胞の損傷、アルファシヌクレインタンパク質の異常蓄積、ミトコンドリア機能異常、そして酸化ストレスなどがパーキンソン病と関連しています。グリホサートはドーパミン神経細胞毒性を誘発したり、ミトコンドリアに損傷を与える可能性があるという動物実験の結果も報告されています。
3. 学界の見解と研究の限界
神経系疾患とグリホサートの関連性は、現在学界で非常に活発に研究されている分野です。しかし、いくつかの限界と論争も存在します。
多因子性疾患： 自閉症、ADHD、認知症、パーキンソン病などは、遺伝的要因、環境的要因、生活習慣など多様な要因が複合的に作用して発生する多因子性（multifactorial）疾患です。したがって、グリホサートがこれらの疾患の「単一の原因」であると主張することは困難です。
相反する結果： 一部の研究ではグリホサートとの関連性を見出していますが、他の研究では関連性を見つけられなかったり、むしろ相反する結果を報告したりすることもあります。このような違いは、研究デザイン、曝露量、対象集団、そして交絡因子の制御などの違いに起因する可能性があります。
バイエル/モンサント側の反論： モンサント（現在バイエルが所有）側は、グリホサートの安全性を継続的に擁護しています。彼らは、当該製品が数十年にわたり広範囲に使用されてきたにもかかわらず、科学的に有害性が明確に証明されていないと主張しています。グリホサートによる訴訟に巻き込まれ、既に巨額の賠償金を支払っており、今も絶え間ない訴訟に巻き込まれているにもかかわらず、このような主張をするのはどう理解すればよいのでしょうか？
悪名高かったモンサントを買収合併し、モンサントが開発したグリホサートのためにこのような金銭的損失を被りながらも、依然としてグリホサートの無害性を主張し、モンサント以外の他の化学農薬会社まで買収する巨大製薬会社バイエル。
白くて丸いものに十字のマークで代表されるアスピリンを生み出したバイエル。後日、バイエルについてもう少し詳しく話す時間を持ちたいと思います。
結論：終わらない科学的論争と私たちの選択
グリホサートの人体への有害性、特に神経系疾患との関連性に関する議論は、依然として進行中の科学的論争です。たとえシキミ酸経路が人間に直接存在しなくても、腸内マイクロバイオームを攪乱し、解毒能力に影響を与え、酸化ストレスを誘発する可能性があるという仮説を通じて、がんを含む様々な疾患との間接的な関連性が継続的に提示されています。
このような不確実性の中で、私たちはどのように対応すべきでしょうか？
予防原則（Precautionary Principle）： 科学的証拠が100%確立されていなくても、潜在的なリスクがあるならば、それを予防するための措置を講じるべきであるという原則です。特に子供や妊婦、免疫力が弱い層には、より重要に適用されるべきです。
情報の批判的受容： 専門家やメディアからの情報を盲目的に受け入れるのではなく、多様な情報源からの情報を批判的に検討し、自ら判断しようと努力することが必要です。
安全な食品の選択： グリホサート残留の懸念がある食品（輸入小麦、トウモロコシ、大豆、レンズ豆以外の豆類など）の場合、可能であれば有機栽培、非GM（Non-GMO）、またはグリホサートフリー認証製品を選択することが、潜在的な曝露を減らす良い方法となりえます。私たちの国産農産物や旬の食品を優先的に選択するのも賢明な方法です。
継続的な研究と政策変更の促進： 学界では、より詳細で独立した研究が活発に進められるべきであり、政府は消費者の安全を最優先とし、化学物質規制および食品安全基準をさらに強化すべきでしょう。
レイチェル・カーソンの『沈黙の春』がDDTの危険性を警告したように、私たちはグリホサートのような現代の化学物質が、私たちの**「沈黙の臓器」**や神経系にどのような影響を与えるのかについて、絶えず問い続け、より良い答えを見つけ出す責任があります。
もしかしたら、この春、アメリカで少々春らしい法案が可決されたことをご存知でしょうか？もし初めて聞く話であれば、夏の初め、地域によっては真夏頃に、季節外れの春の知らせではありますが、それについて話す機会を設けたいと思います。一体どのような話になるのでしょうか？
シェイクスピアの「夏の夜の夢」をもう一度読み返したり、メンデルスゾーンが作曲した「夏の夜の夢」を鑑賞したりしながら、興味を持っていただけると嬉しいです。
「結婚行進曲」を聴きながら過ぎ去った結婚生活を懐かしむひとときや、膨らむ未来に聴くことになる幸せな「結婚行進曲」を夢見る瞬間は、健康な心身にも役立つかもしれません。
ひょっとしたら、こんなことを言う人もいるかもしれません。「あなたの警告はもう十分知っています。グリホサートやGM作物に関連する食材なんて、うちの食卓からはとっくに消えています。とにかく心配してくれてありがとう。他の人はともかく、私にはこういう記事は時間の無駄のように感じます。犬と公園を散歩した後、ゴルフの約束があるので、これで失礼します。」
次回予告： できることなら、犬と公園を散歩に出かける前、あるいはゴルフ場へ車を向ける前に届けられることを期待し、次回の記事は「公園で、ゴルフ場で、思いがけない宿敵との出会い」という話で、必然的（？）に続いていくことでしょう。
参考文献
著者: Mesnage, S., & Antoniou, M. N. 出典: Food and Chemical Toxicology, 2017. タイトル: Ignoring the Obvious: The Scientific and Regulatory Non-Compliance of Glyphosate Risk Assessments. 内容要約: このレビュー論文は、グリホサートの毒性評価における既存の規制枠組みの限界を批判的に検証しています。特に、グリホサート製剤に含まれる他の成分（界面活性剤など）の毒性効果が見過ごされていること、そして長期的かつ複合的な曝露に関する研究が不足していることを指摘しています。グリホサート単一物質ではなく、商業用製剤全体に対する評価が必要であると強調しています。
著者: Van Bruggen, A. H. C., He, M. M., Shin, K., Mai, V., Jeong, K. C., Finckh, M. R., & Gaskell, J. (2018). 出典: Environmental Pollution, 2018. タイトル: Environmental and health effects of the herbicide glyphosate. 内容要約: この論文は、グリホサートの環境および健康への影響を広範囲にわたって検証しています。特に、土壌微生物、水生生態系への影響とともに、人間の腸内微生物、免疫システム、神経系への潜在的な影響を扱っています。グリホサートが微生物に与える影響が食物連鎖を通じて人間の健康にまで連鎖的に影響を及ぼす可能性があることを示唆しています。
著者: Rueda-Ruzafa, L., Cruz, F., Roman, P., & Cardona, D. (2019). 出典: Environmental Research, 2019. タイトル: Gut microbiota and neurological diseases: A systematic review and meta-analysis. 内容要約: この体系的文献レビューとメタ分析は、腸内微生物と様々な神経系疾患（自閉症スペクトラム障害、パーキンソン病、アルツハイマー病、多発性硬化症など）との関連性を探求しています。グリホサートを直接扱っているわけではありませんが、腸脳軸の攪乱が神経系疾患の発症に重要な役割を果たすという一般的な原則を裏付けており、グリホサートが腸内微生物の攪乱を通じて神経系に影響を与える可能性があるという仮説の背景知識を提供します。
著者: Mills, K., Niedzwiecki, A., & Rath, M. (2020). 出典: Journal of Cellular and Molecular Medicine, 2020. タイトル: Review on the mechanisms of action of glyphosate in mammalian systems and its potential link to cancer and other diseases. 内容要約: このレビューは、グリホサートが哺乳類システムで作用するいくつかのメカニズムを詳細に説明し、特にミトコンドリア機能不全、酸化ストレス誘発、DNA損傷（間接的）の可能性などを強調しています。また、グリホサートががんを含む様々な慢性疾患と関連する可能性があるという証拠を総合的に検証し、さらなる独立した研究の必要性を強く訴えています。
著者: Li, C., Seneff, S., & Swanson, N. (2021). 出典: Environmental Science and Pollution Research, 2021. タイトル: Glyphosate, aluminum, and fluoride: A trifecta of toxicity in neurological disease? 内容要約: この論文は、グリホサートがアルミニウムやフッ化物のような他の環境毒素と組み合わさることで、神経系疾患に対して相乗効果をもたらす可能性があるという仮説を探求しています。特に、グリホサートが金属イオンをキレート（結合）する能力と微生物叢への影響を通じて神経毒性経路が強化される可能性を示唆しており、複合的な環境曝露の重要性を強調しています。
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