Sept. 6, 2013 -- A study by researchers at Cambridge University has found that high-income, highly industrialized countries with large urban areas and better hygiene and sanitation have much higher rates of Alzheimer's disease.
They found that countries where all people have access to clean drinking water have 9% higher Alzheimer's rates than countries where less than half of people have access.
Experts say the study is interesting but does not cancel out lifestyle factors such as diet, education, and overall health.
This latest study adds further weight to the "hygiene hypothesis." This theory suggests that certain aspects of modern life, such as antibiotics and clean drinking water, are linked with less exposure to a range of bacteria, viruses, and other microorganisms. This lack of exposure might cause the immune system to develop poorly.
Part of the immune system is a type of white blood cell, called a T-cell, that defends the body against infection. T-cell deficiency has links to the types of inflammation commonly found in the brains of people with Alzheimer's disease.
Study researcher Molly Fox says in a news release: "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."
Using data from 192 countries, the researchers found that those with higher levels of sanitation had higher rates of Alzheimer's.
More urbanized countries had higher rates of Alzheimer's, independent of life expectancy. Countries where more than three-quarters of the population were located in urban areas had 10% higher rates of Alzheimer's compared to countries where less than one-tenth of people lived in urban areas.
Differences in levels of sanitation, infectious disease, and urbanization accounted respectively for 33%, 36%, and 28% of the discrepancy in Alzheimer's rates between countries.
The results of the study are published in the journal Evolution, Medicine, and Public Health.
"A better understanding of how environmental sanitation influences Alzheimer's risk could open up avenues for both lifestyle and pharmaceutical strategies to limit Alzheimer's prevalence,” Fox says. “An awareness of this byproduct of increasing wealth and development could encourage the innovation of new strategies to protect vulnerable populations from Alzheimer's."
Interesting Theory, but
Simon Ridley, head of research at Alzheimer’s Research U.K., says the study is “intriguing” but does not prove that better hygiene causes Alzheimer’s disease. "Our risk of Alzheimer’s is likely to be influenced by a complex mix of environmental and lifestyle factors, and this study did not investigate whether other factors beyond hygiene may be linked to any differing Alzheimer’s risk in different countries."
"Research to understand the different factors affecting the risk of Alzheimer’s is crucial for finding preventions for the disease. Although there is not yet a surefire way to prevent Alzheimer’s, the risk can be reduced by eating a healthy, balanced diet, exercising regularly, not smoking, and keeping blood pressure and cholesterol in check," Ridley says.