A huge study reveals: air pollution is linked to an increase in the risk of Alzheimer’s

During the follow-up period, 2,997,902 participants, which is 10.8% of all subjects, were diagnosed with new-onset Alzheimer’s. Exposure levels to air pollution were calculated based on an average of five years prior to diagnosis, based on pollution data by residential area at the zip code level. The average level of exposure to PM2.5 particles was 10.1 micrograms per cubic meter.

The statistical analysis revealed that for every increase in the particle concentration there was an 8.5% increase in the risk of developing Alzheimer’s, a risk ratio of 1.085. This is a moderate increase, but one that in a broad population may translate into significant numbers of additional patients.

Hypertension, stroke and depression were indeed found to be each independently associated with an increased risk of Alzheimer’s. However, mediation analyzes showed that their contribution to explaining the connection between the infection and Alzheimer’s was only limited. Hypertension was associated with 1.6% of cases, stroke 4.2%, and depression 2.1%. This means that most of the impact of air pollution is not explained through these diseases.

The striking finding was that among people with a history of stroke the link between air pollution and Alzheimer’s was stronger, risk ratio 1.105. Conversely, hypertension and depression did not substantially change the strength of the relationship. The researchers believe that people with a previous brain injury may be more vulnerable to the toxic effects of respirable particles.

The researchers hypothesize that the possible mechanisms of action include penetration of tiny particles through the respiratory system into the blood circulation, and from there to the brain, creating chronic inflammation, oxidative stress and damage to tiny cerebral blood vessels. Previous studies have shown that these particles may be found in brain tissue and even accelerate the accumulation of typical pathological proteins in the brains of Alzheimer’s patients.

Alzheimer’s disease is a progressive degenerative brain disease and the most common cause of dementia in old age. It is characterized by the accumulation of pathological proteins in the brain, including amyloid and beta tau, which cause gradual damage to nerve cells and loss of connections between them. In the first stages, damage to short-term memory, difficulty in retrieving words and orientation in space and time often appears.

Later on, changes in behavior and personality are added, a decrease in the ability to make decisions and damage to daily functioning up to a complete loss of independence. The disease progresses over years, and although there are treatments aimed at slowing the deterioration or relieving symptoms, currently there is no treatment that cures the disease or stops it completely.

Air pollution has been linked to a long list of chronic diseases in the past. Among other things, a link between prolonged exposure to respirable particles and cardiovascular diseases, myocardial infarction, stroke, heart failure and arrhythmias has been proven. A connection was also found with an increase in the rate of lung cancer, exacerbation of asthma and chronic obstructive pulmonary disease, type 2 diabetes, premature births and low birth weight. In recent years, data has also been accumulating on a link to mild cognitive disorders and a decline in memory even before the onset of dementia.

The World Health Organization has already defined air pollution as one of the main environmental risk factors for global morbidity and mortality. It is estimated that millions of deaths per year are attributed to chronic exposure to pollution, mainly in urban areas with heavy traffic.

Along with the limitations, which include relying on data from administrative claims and estimating exposure by residential area and not by personal measurement, the sample size and the strict methodology strengthen the findings. The researchers adjusted the models for age, sex, origin, socioeconomic status, geographic region, smoking rates, body mass index, access to health services and other variables.

“The findings strengthen the hypothesis that the air we breathe over the years may shape the aging process of the brain,” the researchers concluded. “Air pollution is seen as a modifiable risk factor, that is, one that can be influenced through public policy, reducing emissions and improving the quality of the environment. Investing in reducing air pollution may be part of a dementia prevention strategy, alongside controlling vascular risk factors, physical activity and maintaining a balanced diet.”