In a quest to make our surroundings germ-free, we might have blocked all the good bacteria from our lives that have now led to the rise of Alzheimer's disease, say researchers at Cambridge University.
Researchers hypothesize that high rates of Alzheimer's disease in wealthy nations may be linked to the increased levels of sanitation. The idea isn't new; previous research has associated higher stroke risk to disappearing number of gut bacterium Helicobacter pylori (H. pylori).
The new study adds evidence to the hygiene hypothesis, according to which people in developed nations are less exposed to bacteria, viruses and other microbes which prevents the immune system from functioning properly.
"The 'hygiene hypothesis', which suggests a relationship between cleaner environments and a higher risk of certain allergies and autoimmune diseases, is well- established. We believe we can now add Alzheimer's to this list of diseases," said Dr Molly Fox, Gates Cambridge Alumna, who conducted the research at Cambridge's Biological Anthropology division and lead author of the study.
The study was based on data from 192 countries. Researchers found that in countries where everybody had access to clean drinking water such as France, there was a 9 percent higher prevalence of AD when compared to poor nations such as Cambodia or Kenya.
Living in urban areas also increased AD rate. In Australia and the U.K., where over 75 percent of the population lives in urban areas, there were 10 percent higher AD rates than countries like Nepal, where just a tenth of the population lives in cities, according to a news release.
Countries with higher rates of infectious diseases such as China had lower rates of AD when compared to other countries Like Switzerland, where infectious disease rates are low.
Experts said that despite other factors that may explain the difference of AD rates between countries, hygiene singularly accounted "for 42.5% of the "variation" in the countries' Alzheimer's disease rates."
For many centuries, humans have lived along with animals and microbes. But, the developed countries have paved roads, clean drinking water and access to antibiotics, which doesn't let the immune system develop. Researchers attribute AD risk to the poorly developed white blood cells that help the body fight foreign invaders.
Lack of T-cells has been linked with the kind of inflammation seen in people with Alzheimer's disease, researchers said.
The study is published in the journal Evolution, Medicine and Public Health.
Latest data from the Alzheimer's Association shows that over 5 million people in the U.S. have AD, a number that is expected to explode to 13. 8 to 16 million people by 2050.