Few would argue the overall health benefits of living in the industrialized world. Clean drinking water, fewer fatal accidents and greatly reduced infant mortality are just a few of the advantages. So pronounced are the health boons of development that researchers may sometimes be blinded to health risks that it brings.
For example, rates of Alzheimer’s disease are higher in developed nations — a fact that is often attributed to the longer life expectancies in those countries. But the higher rates persist even after correcting for longer lifespans, according to a recent study led by Cambridge evolutionary biologist Molly Fox.
With that in mind, it seems there must be health threats in the developed world that aren’t present in countries that have stuck to their agrarian traditions. Fox’s study suggested that, paradoxically, the improved sanitation in developed countries may leave residents more exposed to Alzheimer’s disease.
The study is apparently the first to link Alzheimer’s disease to an increasingly accepted theory called the hygiene hypothesis.
The hypothesis posits that people in industrialized societies don’t come into contact with enough bacteria to spur their immune systems to develop fully. Some, like Fox, focus on the development of germ-killing T-cells in young children.
The hygiene hypothesis has previously been cited as a possible cause for autoimmune disorders, allergies, asthma and even diabetes — all of which have increased rapidly enough to defy conventional explanations.
“In the modern developed world, we live in hygienically sanitized environments, and as a result we’re not in contact with animals, feces and mud, which would have been the norm for the vast majority of human history,” Fox said in a video about the findings, published in published in Evolution, Medicine and Public Health.
Industrialization freed us not just the bacteria that cause fatal bouts of diarrhea in the developing world, but also bacteria with which humans have co-evolved to have a symbiotic relationship, such as those that dwell in healthy intestinal systems and may help keep us thin.
Fox and her co-authors specifically linked better sanitation with higher rates of Alzheimer’s disease. They identified countries with poor water sanitation systems, large rural populations and high rates of infectious disease, all of which indicate that residents come into contact with more microbes. Then they compared those countries’ rates of Alzheimer’s disease with those of developed countries, adjusting for life expectancy. They found that differences in levels of sanitation, infectious disease and urbanization accounted statistically for about a third of the discrepancy in Alzheimer’s rates between countries.
The findings, while more suggestive than conclusive, jibe with some recent medical research into Alzheimer’s disease.
Researchers have focused on the inflammation found in the brains of those who suffer from Alzheimer’s disease, and the middling immune systems attributed to the hygiene hypothesis are blamed for excessive inflammation. Other recent Alzheimer’s research has identified the failure of the brain’s immune function to “take out the trash” that accumulates from normal cell function.
If medical and public health research support a similar cause for the disease, it may guide them to more successful new prevention and treatment prospects.
“An awareness of this by-product of increasing wealth and development could encourage the innovation of new strategies to protect vulnerable populations from Alzheimer’s disease,” Fox told Singularity Hub.
Real answers about Alzheimer’s disease are still seemingly far off. But the growing body of research across individual diseases backing the hygiene hypothesis could bring new ideas about how industrializing countries might share in the benefits of development without battling microbes as zealously as the West once did.
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