Urban areas are centers of bustling activity, which can provide ample opportunities for cognitively stimulating activities, but also increase exposure to excessive noise, commonly referred to as noise pollution. Exposure to noise can lead to short term impairments in cognitive function, particularly with respect to the ability to focus and remember, while some studies suggest that, similar to air pollution, chronic exposure to noise pollution may increase the risk for dementia.
A report by the European Environmental Agency found that 12,000 premature deaths and 48,000 cases of ischemic heart disease were attributable to environmental noise pollution each year in Europe [1]. The majority of the noise pollution is related to traffic. Sound is measured on a decibel (dB) scale where zero decibels is the softest sound a human can detect and the intensity of the sound doubles every three decibels [2]. For health measures, sound levels are often reported as dB(A), which is adjusted to account for how well humans can hear different sound wave frequencies. Advisory guidelines use the threshold of 50 to 55 dB(A) to classify environmental noise levels that are potentially hazardous to human health [3]. According to the Environmental Protection Agency, noise levels above 70 dB(A) can lead to hearing loss [2].
In a study of 5,227 residents of the Chicago area, global cognitive performance varied with the local neighborhood noise level [4]. The residential noise levels varied from 51.1 to 78.2 dB(A). Each 10 dB(A) increase in residential noise level was associated with a 36% increase in the risk for mild cognitive impairment (MCI) and a 29% increase in the risk for Alzheimer’s disease. A study of 4,086 residents in Germany found a similar association regarding the increased risk for MCI in participants exposed to the highest residential noise levels, or greater than 60 dB(A) [5]. Based on the assessment of 130,978 residents of London, those exposed to the highest noise levels, greater than 53.8 dB, during the night had a 9% higher risk of developing dementia [6].
In the majority of cases, residents living in areas with the highest levels of noise pollution were also exposed to higher levels of air pollution and were more likely to have lower socioeconomic status. Since all of these factors impact dementia risk, it can be difficult to tease out the exact contribution of noise. The evidence suggests that each of these factors acts as a stressor, and that it is the lifetime burden of all stressors that influences overall dementia risk [7].
However, noise is a rather unique stressor in that the response to a particular sound stimulus is very subjective because it depends on whether a person perceives the sound as bothersome [3]. If someone is bothered by a sound, then it can induce a stress response in the body and lead to negative health effects. But, if someone can easily tune out the sound, then it is unlikely to produce ill effects in that person. The response to a sound depends on the type, duration, and loudness of the sound itself, as well as factors intrinsic to the person, such as personality. People high in the personality trait of neuroticism, who are more prone to anxiety and depression, tend to be more sensitive to noise and are more likely to experience negative effects following noise exposure [3].
Noise acts as a stressor by inducing a state of arousal in the body, which increases levels of stress hormones, such as cortisol. The brain is wasting resources on trying to tune out the noise, so the brain has less capacity to perform other complex tasks, leading to a temporary decline in cognitive performance [3]. Attention and memory tend to be the cognitive domains most impacted by noise. The stress response leads to vascular changes that can pave the way for cardiovascular disease and vascular dementia. Meta-analyses indicate that each 10 dB(A) increase in environmental noise increases the risk for adverse cardiovascular outcomes, including hypertension and heart attacks, by 7 to 17% [8]. Due to the strong connection between heart health and brain health, these negative effects on the cardiovascular system may account for some of the increased dementia risk from noise pollution. Exposure to noise during the night can impair sleep quality, which has additional negative health consequences. Chronic activation of the arousal-stress response can also cause oxidative stress, which is another driver of dementia.
Noise may be particularly problematic for people with dementia because they do not have enough brain resources to filter the noise and perform other cognitive functions at the same time. Individuals with dementia may need a period of uninterrupted silence to allow them to fully utilize their limited cognitive resources, which may lead to more meaningful interactions.
Since moving away from an area of high noise pollution is not a feasible solution for most people, the best solution for reducing the health hazards of noise involves practicing stress mitigation techniques, such as meditation or yoga.
Betsy Mills, PhD, is a member of the ADDF's Aging and Alzheimer's Prevention program. She critically evaluates the scientific evidence regarding prospective therapies to promote brain health and/or prevent Alzheimer's disease, and contributes to CognitiveVitality.org. Dr. Mills came to the ADDF from the University of Michigan, where she served as the grant writing manager for a clinical laboratory specializing in neuroautoimmune diseases. She also completed a Postdoctoral fellowship at the University of Michigan, where she worked to uncover genes that could promote retina regeneration. She earned her doctorate in neuroscience at Johns Hopkins University School of Medicine, where she studied the role of glial cells in the optic nerve, and their contribution to neurodegeneration in glaucoma. She obtained her bachelor's degree in biology from the College of the Holy Cross. Dr. Mills has a strong passion for community outreach, and has served as program presenter with the Michigan Great Lakes Chapter of the Alzheimer's Association to promote dementia awareness.
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