A Danish study conducted over the span of 13 years has found that exposure to noise pollution from road and railway traffic can increase the risk of developing dementia.
The noisier, the more susceptible
The study sampled two million adults over the age of 60 and found that 1,216 out of the 8,475 cases of dementia registered in Denmark in 2017 could be attributed to noise exposure. Scientists found that people who were regularly subject to noise of 55 decibels and over were 27% more likely to develop Alzheimer's—which happens to be the most common cause of dementia.
When compared to people sampled who lived in quieter areas where traffic noise was no louder than 40db, those who who constantly surrounded by traffic noise upwards of 50db saw a 24% increase in being afflicted by dementia.
Why does traffic noise cause dementia?
One theory for such results according to researchers is attributed to the release of stress hormoneswhen sleep is interrupted. In the past, stress levels have been observed to have a direct impact on one's immune system. Study author, Dr. Manuella Lech Cantuaria explained that:
Epidemiological studies have consistently linked transportation noise to various diseases and health conditions, such as coronary heart disease, obesity and diabetes.
The proposed biological mechanisms are noise-induced reactions, with activation of the autonomic nervous and the endocrine (hormone) system and subsequent release of stress hormones, affecting several physiological functions.
Exposure to noise during the night can also lead to sleep disturbance and fragmented sleep. Experimental studies have found associations between transportation noise at night time and endothelial dysfunction, increased oxidative stress, alterations in the immune system, and increased systemic inflammation.
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