Vehicular traffic and certain industrial activities generate PM2.5 fine particles, so called because they are smaller than 2.5 microns in size, allowing them to enter the lungs. These particles pollute the air we breathe and have been associated with numerous health problems. In fact, a recent study has linked exposure to these environmental pollutants with the development of lung cancer in non-smokers.
Now, a meta-analysis by scientists at the Harvard TH Chan School of Public Health has confirmed the results of previous studies linking breathing air pollutants, especially PM2.5, to the development of dementia. There are currently more than 57 million people in the world who suffer from dementia, and it is estimated that by 2050 the number of patients will reach 153 million. Up to 40% of these cases would be related to risk factors that can be modified, such as exposure to air pollutants.
“This is a big step in providing actionable data for regulatory agencies and clinicians in terms of making sense of the state of the literature on this highly important health topic. The results can be used by organizations such as the Environmental Protection Agency, which is currently considering strengthening exposure limits for PM2.5,” said lead author Marc Weisskopf, Cecil K. and Philip Drinker Professor of Environmental Epidemiology and Physiology. “Our findings support the importance of such a measure for public health.”
PM2.5, nitrogen oxide and nitrogen dioxide associated with dementia
The researchers reviewed more than 2,000 studies and identified 51 that had examined an association between air pollution and clinical dementia that had been published in the last decade. After assessing the bias of these studies, they selected 16 that met the criteria for meta-analysis. Most of the research focused on PM2.5, with nitrogen dioxide and nitrogen oxide being the other two most common pollutants studied.
There is consistent evidence of an association between PM2.5 exposure and dementia, even when annual exposure was below the Environmental Protection Agency standard of 12 μg/m3
The results showed consistent evidence of an association between PM2.5 exposure and dementia, even when annual exposure was below the current Environmental Protection Agency (EPA) annual standard of 12 micrograms per cubic meter of air ( µg/m3). Among studies using active case finding, scientists found a 17% increased risk of developing dementia for every 2 μg/m3 increase in average annual PM2.5 exposure.
They also found evidence suggesting associations between dementia and nitrogen oxide (5% increase in risk for every 10 μg/m3 increase in annual exposure) and nitrogen dioxide (2% increase in risk for every 10 μg /m3 increase in annual exposure). The findings have been published in The BMJ.
Researchers have noted that the estimated association of air pollution with dementia risk is less than that of other risk factors, such as education level and smoking, but that when one takes into account the large number of people exposed to air pollution the health implications at the population level could be significant.
“Given the enormous number of dementia cases, identifying actionable modifiable risk factors to reduce the burden of disease would have tremendous personal and societal impact,” Weisskopf says. “Exposure to PM2.5 and other air pollutants is modifiable to some extent by personal behaviors, but more importantly, through regulation.”
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