A new study by researchers from Canada and the UK has reported that individuals living in wealthier countries with better access to clean water and good hygiene may have a higher risk of developing Alzheimer’s disease. Their findings were published online on August 11 in the in the journal Evolution, Medicine and Public Health.
Alzheimer’s disease is a chronic condition that involves a decline in mental function; it accounts for 70% of all cases of dementia. According to the Los Angeles County Department of Public Health, Alzheimer’s disease is the seventh leading cause of death in both Los Angeles County and the rest of the United States. Currently, at least 147,000 Angelenos are living with the disease, more than 300,000 LA adults are providing care to Alzheimer’s sufferers, and more than 326,000 baby boomers in the county are expected to develop the disease during their lifetime. According to the new study, if an Angeleno had been born in a developing nation, which lacked all the amenities found in LA, the risk of developing the disease would be significantly less.
The question becomes: why? The answer lies in the fact that Alzheimer’s disease has some of the characteristics of an autoimmune disease. The study authors noted that the prevalence of autoimmunity varies between populations in accordance with variation in environmental microbial diversity. They note that studies have reported that exposure to microorganisms may improve a person’s immune system in ways that protect against autoimmunity; therefore, they suggest that this process may be involved in the development of Alzheimer’s disease. To test this theory, they analyzed data from the World Health Organization's (WHO) Global Burden of Disease (GBD) report in 2009.
The investigators developed statistical models to test whether pathogen prevalence in 192 nations can explain a significant amount of the variation in age-standardized Alzheimer’s disease disability-adjusted life-year (DALY) rates. They also reviewed and assessed the relationship between pathogen prevalence and Alzheimer’s disease rates in different world populations.
The researchers found that hygiene is positively associated with Alzheimer’s disease risk. Nations with a greater degree of sanitation and lower degree of pathogen prevalence have higher age-adjusted Alzheimer’s disease DALY rates. Furthermore, nations with a greater degree of urbanization and wealth exhibit higher age-adjusted Alzheimer’s disease DALY rates.
The study authors concluded that variation in hygiene may partly explain global patterns in Alzheimer’s disease rates. Microorganism exposure may be inversely related to Alzheimer’s disease risk, meaning the greater the exposure, the less the risk. They noted that their findings may help predict Alzheimer’s disease burden in developing nations where microbial diversity is rapidly diminishing. They wrote: “Epidemiological forecasting is important for preparing for future healthcare needs and research prioritization.”
Take home message:
The researchers focused on assessing the risk of Alzheimer’s disease in developing nations; however, it can also have implications for developed nations such as the US. If autoimmune factors in Alzheimer’s disease can be clarified, the findings may lead to immunizations that can offer protection from the disease.