Many people have asked me what was the most interesting thing I learned at the Alzheimer Europe conference in Geneva. It was the impact of noise pollution on our physical health.
A 14-year study involving almost 2 million Denmark residents aged over 60, found that exposure to road traffic and railway noise increased the risk of all dementias, especially Alzheimer’s. Other studies have linked transportation noise to coronary heart disease, obesity, and type 2 diabetes, through release of stress hormones (cortisol and adrenaline), alterations in our immune system, increased inflammation and sleep disturbances. All these factors also play a role in the development of dementia.
Untreated hearing loss in midlife is also a risk factor for developing dementia via several proposed mechanisms:
- Use it or lose it. If the regions of our brain responsible for processing sound are not stimulated, those parts of our brain shrink (atrophy) from lack of use. This is known as ‘the cascade hypothesis’.
- A person with diminished hearing needs to concentrate harder to follow conversations, which drains energy from other brain functions such as memory. Diverting more brain resources to hearing can also cause structural brain changes that contribute to cognitive decline. This is known as ‘the cognitive load hypothesis’.
- Hearing loss also contributes to depression, social isolation, stress and high blood pressure. These things all independently increase dementia risk. Therefore, if hearing loss contributes to these conditions, hearing loss will also propel a person towards dementia.
Predictably, the more severe the hearing loss, the greater the risk of dementia.
However, there is good news.
People with hearing impairment who use hearing aids or cochlear implants to restore their hearing to normal levels, are no more likely to develop cognitive impairment than people without hearing loss. Another little known fact is that physical exercises reduces the loss of hair cells in our cochlea (the bone in our ear where sound vibrations are converted to nerve impulses). Sedentary mice lose about 20% of their hearing as they age. Mice that run on treadmills every day only lose 5% of their hearing. As if you needed another reason to exercise.
What surprised me, however, was that even in the absence of hearing loss, people exposed to high residential noise (more than 60 decibels) had a 19-22% increased risk of type 2 diabetes, and were more likely to develop obesity. Traffic and aircraft noise were particularly hazardous, probably because they also contribute to air pollution (another major disease-promoting agent).
Traffic noise was also found to impair our metabolism, damage blood vessels, raise heart rate and blood pressure, and increase the risk of stroke and heart failure. What’s bad for the heart is also bad for the brain. The brain uses one fifth of our blood supply, and if that blood supply is compromised, so is brain function.
More research is needed to determine exactly how much noise, for how long, and what type (for example, high or low frequency) starts to damage our health. Expanding our knowledge of the harmful effects of noise pollution is critical for informing public health policies that could improve the lives of millions of people throughout the world.
In the meantime, I aim to protect my hearing and avoid exposure to loud noises as much as possible. Wearing ear plugs during gym classes and while sleeping in hotel rooms that are exposed to heavy traffic noise is a start.
Please share this Health-e-Byte to anyone who is starting to lose their hearing or is exposed to loud noises on a regular basis — including discoes and fitness classes!
Photo credit: I took this photo while strolling through Jardin Angliais (English Garden) on Geneva’s lakefront. It was the perfect antidote to noise pollution.
