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Air pollution linked to increased risk of dementia

Exposure to fine particulate air pollutants, also known as PM2.5, may increase the risk of developing dementia, according to a new meta-analysis conducted by researchers at Harvard T.H. Chan School of Public Health

Dementia is a syndrome that affects cognitive function, including memory, thinking, language, and the ability to carry out daily activities. It is caused by damage to the brain cells and can be progressive, meaning it gets worse over time.

Dementia can have a significant impact on a person’s life, including their ability to communicate, their mood and behavior, and their independence. People with dementia may experience memory loss, difficulty with language, confusion, personality changes, and impaired reasoning and judgment. 

Individuals who suffer from dementia may also have difficulty with everyday tasks, such as dressing, grooming, and eating. As the condition progresses, individuals may require increasing levels of care and support from their loved ones or healthcare professionals.

The study is the first systematic review and meta-analysis to use the new Risk of Bias In Non-Randomized Studies of Exposure (ROBINS-E) tool, which addresses bias in environmental studies in greater detail than other assessment approaches. It is also the first to include newer studies that used “active case ascertainment,” a method that involved screening entire study populations followed by in-person evaluation for dementia among individuals who did not have dementia at baseline.

The researchers identified 51 studies that evaluated the association between ambient air pollution and clinical dementia, all published within the last ten years. The studies were assessed for bias using ROBINS-E, and 16 of them met the criteria for the meta-analysis. 

The majority of the research was focused on PM2.5, with nitrogen dioxide and nitrogen oxide being the next most common pollutants studied. Of the studies used in the meta-analysis, nine used active case ascertainment.

The researchers found consistent evidence of an association between PM2.5 and dementia, even when annual exposure was less than the current EPA annual standard of 12 micrograms per cubic meter of air (μg/m3). Among the studies using active case ascertainment, the researchers found a 17-percent increase in risk for developing dementia for every two μg/m3 increase in average annual exposure to PM2.5. 

They also found evidence suggesting associations between dementia and nitrogen oxide (five percent increase in risk for every 10 μg/m3 of annual exposure) and nitrogen dioxide (two percent increase in risk for every 10 μg/m3 of annual exposure), though the data was more limited.

“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 hugely important health topic,” said study lead author Professor Marc Weisskopf. “The results can be used by organizations like the Environmental Protection Agency, which is currently considering strengthening limits on PM2.5 exposure. Our findings support the public health importance of such a measure.”

More than 57 million people worldwide are currently living with dementia, and estimates suggest that number will increase to 153 million by 2050. Up to 40 percent of these cases are thought to be linked to potentially modifiable risk factors, such as exposure to air pollutants. 

Air pollution’s estimated association with the risk of dementia is smaller than that of other risk factors, such as education and smoking. However, because of the number of people exposed to air pollution, the population-level health implications could be substantial.

“Given the massive numbers of dementia cases, identifying actionable modifiable risk factors to reduce the burden of disease would have tremendous personal and societal impact,” said Professor Weisskopf. “Exposure to PM2.5 and other air pollutants is modifiable to some extent by personal behaviors—but more importantly through regulation.”

Air pollution is caused by the release of harmful substances into the air by human activities such as transportation, industrial processes, and energy production. These substances can include particulate matter, nitrogen oxides, sulfur oxides, carbon monoxide, ozone, and volatile organic compounds.

The impact of air pollution on the planet can be significant. Particulate matter, for example, can cause respiratory problems and other health issues in humans and animals. Nitrogen oxides and sulfur oxides can lead to acid rain, which can damage crops and forests, harm aquatic life, and erode buildings and monuments. Ozone, when it is present in the lower atmosphere, can be harmful to human health and vegetation.

Air pollution also contributes to climate change. Carbon dioxide, which is released through the burning of fossil fuels, is a greenhouse gas that traps heat in the atmosphere and contributes to rising global temperatures. This can lead to a range of impacts, including sea level rise, changes in weather patterns, and more frequent and severe natural disasters such as floods, hurricanes, and wildfires.

Overall, air pollution has significant negative impacts on both human health and the environment, and addressing this issue is crucial for creating a sustainable and healthy future for our planet.

The study is published in the journal The BMJ.

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