How environmental toxins can affect the human brain and increase the risk of Alzheimer’s disease
We, the team of “Knowledge stops dementia”, have started to provide you the latest scientific studies regarding the problem concerning toxins and contaminants and to make this information available on our homepage in a newly designed chapter. For our environment has changed profoundly in the last hundred years: While humans have been evolving for over 4.5 million years, it is only in the last 100 years that over 90,000 new chemical agents have become part of almost every aspect of human life (1). Such products are not only an important part of our daily activities through what we eat, drink, breathe, and lather onto our skin, but they have also been absorbed into our tissues. Now, laboratory tests can detect many of these chemicals in our blood, urine, placenta, breast milk, and semen. From the day of conception to the latent breath we take, exposure to thousands of harmful chemicals has become part of the human experience, and also have to get rid of them when we absorb them.
The link between exposure to environmental pollutants and Alzheimer’s disease, although not fully proven, has been confirmed in scientific studies for many years. Individuals who are exposed to pollutants (through occupational exposure or by living in regions with high levels of environmental pollutants) or who have higher blood levels of toxic and harmful substances have a higher risk of developing dementia.
In 2020, the report of the commission on “Dementia Prevention, Intervention, and Care” of the well-known medical journal The Lancet Neurology added “air pollution” to the list of modified risk factors that could help prevent dementia: “Airborne particulate pollutants accelerate neuro- degenerative processes through cerebrovascular (affecting the cerebral circulation) and cardiovascular (affecting the cardiac circulation) disease, Alzheimer-specific deposits (amyloid-beta proteins) and the processing of their precursor proteins. High nitrogen dioxide concentration, fine ambient particulate matter from traffic exhaust and from residential wood burning are associated with increased dementia incidence” – states on the report.
But not only particulate matter, also many other environmental contaminants (such as pesticides, metals, mold toxins, microplastics, mineral oils, industrial excipients such as plasticizers, food additives, etc.), recreational substances such as alcohol and tobacco, but also medications (such as anticholinergics prescribed for numerous indications) can be associated with an increased risk of Alzheimer’s disease.
But how do contaminants and toxins affect the nervous system and cause neurodegeneration?
Different mechanisms are involved:
- Destruction of the blood-brain barrier: Some toxins, such as heavy metals, increase the permeability of the blood-brain barrier and can trigger the entire neurodegeneration process observed in Alzheimer’s disease.
- Oxidative stress: the vast majority of toxic agents act through oxidative stress, i.e., a sharp increase in free radical production in the absence of adequate antioxidants. Signs of oxidative damage precede other pathological events in AD and are an early event in the pathogenesis of the disease
- Protein aggregation: Environmental neurotoxicants can disrupt protein processing and lead to neurodegeneration. Amyloid beta and tau protein deposition can be triggered by the presence of certain toxins in the nervous system.
- Mitochondrial dysfunction: environmental toxins can impair mitochondrial function, disrupting the energy supply to nerve cells and leading to neuro-degeneration.
- Dysfunction of the brain – gut axis: Brain health is influenced by the health of the gut, or more specifically the gut microbiome. The gut microbiota modulates neuroinflammation and have therefore a role in neurodegeneration. Some toxic substances can induce gut dysbiosis, i.e, imbalance of the gut microbiota.
- Inflammation: Toxic substances and contaminants can trigger inflammatory response, including an excessive production of pro-inflammatory cytokines. These substances impair neuronal health and function. Alzheimer’s disease is known as a disease of chronic systemic inflammation, which is a result of contributions from many factors, including environment toxic substances.
A major problem that must be considered in relation to toxins and contaminants is the phenomenon of bioaccumulation. Long-term exposure to the same environmental pollutant, even in small amounts, can accumulate in organs and tissues over a lifetime and can lead to adverse health consequences, especially when the body’s own detoxification system reaches its limits or the substances are difficult to eliminate. Some studies show that such accumulation can trigger inflammation in the central nervous system (neuroinflammation) and cause a chain of neuropathological changes leading to the development of Alzheimer’s disease and other neurodegenerative diseases.
In addition, there are a growing number of studies looking at the impact of early childhood exposure to pollutants on neurological disorders such as Alzheimer’s disease, Parkinson’s disease, as well as developmental neurological disorders such as autism spectrum disorders and attention deficit hyperactivity disorder ADHD. It is already known that early life is critical for brain maturation and that numerous environmental factors that occur during this time can significantly affect the long-term functionality of the brain, which in turn has strong implications for lifelong (neuronal) health.
Here it becomes clear that the prevention of Alzheimer’s disease is also linked to the control of the environment and the toxins we come into contact with in our daily lives. For this purpose, on the one hand, the exposure to these brain-toxic substances should be controlled, and at the same time, our body’s ability to excrete the toxins again should be optimized. We must also highlight that preventive measures must begin in childhood, since the developing brain is more susceptible to the negative action of environmental substances.
Some special features of the human brain make it very susceptible to the effects of toxins present in the environment. Many substances such as pesticides, particulate matter/air pollution, heavy metals, industrial excipients, drugs, etc. have been associated with promoting neurodegeneration and increasing the risk of dementia. There are many different mechanisms by which contaminants and toxins can affect the brain and promote neurodegeneration: Inflammation, oxidative stress, mitochondrial dysfunction, altered gut microbiota, and increased formation of abnormal proteins. It is important to note that even small amounts of the same toxin or contaminant ingested over an extended period of time can accumulate in the brain and lead to adverse health consequences. Therefore, it is especially important to keep exposure to these brain toxic substances as low as possible, to detect possible exposures through laboratory diagnostics, and at the same time also to optimize our body’s ability to get rid of the toxins.
Children are particularly vulnerable to these negative effects, and substance exposure in childhood can also increase the risk of neurodegenerative diseases later in life. They need to be even more protected!
For more information on the effects of toxins and contaminants and the risk of Alzheimer’s disease, see our newly redesigned chapter “Reducing Toxins” on the KsD site. Read here, among other things, why the brain in particular, and especially the child’s brain, is so susceptible to harmful and toxic substances and what is already known about certain substance groups such as pesticides and anticholinergics in this context. We are constantly expanding this chapter and will keep you up to date with further contributions, helping you to stay informed and to be able to protect yourself from environmental toxins in the best possible way in the future!
- Cohen A, Vom Saal F. Non-Toxic: A guide to living healthy in a chemical world, Oxford University Press 2020
- Cannon JR, Greenamyre JT. The role of environmental exposures in neurodegeneration and neurodegenerative diseases. Toxicol Sci. 2011 Dec;124(2):225-50. doi: 10.1093/toxsci/kfr239. Epub 2011 Sep 13. PMID: 21914720; PMCID: PMC3216414