A recent study shows that a combination between infections and exposure to traffic-related air pollution caused the increase of Alzheimer’s disease by 177% in 100.000 individuals. That’s an absolutely mind-blowing number, isn’t it ?
Alzheimer’s disease is a “multifactorial” condition, meaning it develops only when multiple risk factors come together to affect an individual, ultimately leading to the clinical stage of the disease.
Risk factors include high exposure to traffic-related air pollution (TRAP) and infections, as well as factors such as hypertension, depression, sleep disorders, brain trauma, and also genes and their components. In a previous study, the researchers found a significant synergistic effect of TRAP and APOE4 on hippocampal volume, a biomarker for neurodegeneration.
In this study, researchers examined factor risks that could increase the risk of AD synergically, because identifying this type of combination helps us understand, even just a little, how the disease works. Also, discovering multi risk factors in the preclinical stage may help us prevent AD in many patients.
The researchers analyzed data from the UK Biobank, including 51,079 women and 48,983 men aged 60-75, with information on infectious diseases, Alzheimer’s disease (AD), and other forms of dementia. They classified high exposure to traffic-related air pollution (TRAP) as living within 50 meters of a major road.
Overall, the presence of both a history of infections and exposure to TRAP was associated with 164% higher risk for AD onset after age 75 years, compared with individuals with neither infection history nor TRAP exposure.
One of the principal mechanisms is the compromise of brain-blood barrier, which makes the brain much more vulnerable to infections and related damage. Prevention of AD remains as a main strategy, giving the limited treatment options.
A key limitation of the study is its reliance on ICD codes to identify infections, which may lead to measurement errors. For instance, patients might be labeled as having an infection based on suspicion alone, even if further evaluation rules it out.
Additionally, measurement errors could vary depending on individuals risk levels for Alzheimer’s disease (AD). Older adults with more AD risk factors might be more likely to seek medical care for mild infections, resulting in more frequent documentation of ICD codes, whereas younger, healthier individuals may be less likely to seek care, potentially skewing the data.
The air pollution information is based on people’s address, and as we all know, not all people spend the same amount of time at their houses, which creates a lot of bias. Additional research may be really helpful in the future to determine AD causes, and also the relationships between the disease air pollution and infections.
Although there aren’t enough reasons explaining the causality, there is no problem in suggesting and recommending people to take precautions to prevent infections and to minimize air pollution’s exposure.
