ALZHEIMER’S DISEASE LINKED TO CITY POLLUTION?. Cause and effect?. If a cause then what is the mechanism?. More and more recent studies show a strong connection between exposure to airborne particles from car exhausts and Alzheimer’s disease (and possibly Lewy Body disease). The tiny airborne particles (Particulate Matter or PM 2.5), 1/30th diameter of a human hair) probably enter the brain via the nose, olfactory (smell) nerve and olfactory bulb or via a weakened ‘blood-brain barrier’. They may act by triggering cytokine release in microglial brain cells, thereby causing inflammatory changes – which may lead to Alzheimer’s disease. They accumulate over many years and may particularly affect people at risk (e.g. via apoe4 genetic predisposition). Other components in polluted city air may also be involved in the increased risk which has been found to be associated with urban life and particularly living close to busy roads. One odd discrepancy in this observation is that Parkinson’s disease has been found to occur at higher rates in association with rural living and particularly with living in places where water is obtained from ground sources (wells, bores). One suggested explanatory risk factor in rural settings may be one of the chemicals sprayed on crops (such as the herbicide, paraquat). Again, as with the urban story there is probably, on an individual basis, an interaction between this apparent rural risk factor and individual risk, including genetic factors.
https://www.scientificamerican.com/article/the-new-alzheimers-air-pollution-link/