The NordSOUND project

Noise and health

Exposure to noise is unavoidable in urban environments. Increasing traffic in all modes of transport, combined with the construction of roads and residential buildings in closer proximity, has led to a general rise in noise exposure.
At least one million healthy life years are lost each year due to traffic noise in Western Europe, and traffic noise has recently been reported to be the second worst environmental exposure in terms of disease burden, after air pollution. At the same time, many people are exposed to high levels of noise in their work environment. Hence, a large fraction of the urban population is exposed to high levels of noise during the whole day, without access to a restorative environment at either work or home. Despite this, almost no studies have aimed at investigating the joint effect of these frequent exposures on the health of the population.

How can noise affect human health?

Hearing is a permanent process essential for human survival and communication. However, as we are not able to shut out noise, exposure can have a number of unwanted effects. Noise is a known psychological and physiological stressor. It can trigger a classic stress response, with activation of the autonomic nervous system and the endocrine system, leading to a cascade of effects, including rise in heart rate, blood pressure, and levels of stress hormones (cortisol, adrenalin and noradrenaline). This general stress response is a physiologic acute adaptation to stress, which may ultimately lead to pathophysiologic alterations if the exposure is chronic, resulting in health effects.
While the conscious experience with noise may be the primary source of stress during daytime, the unconscious response during nighttime sleep, is thought to play a particularly important role in effects of traffic noise on health. Exposure to transportation noise at normal urban levels has been shown to result in sleep disturbances from sleep stage changes to full awakening. Recent experimental studies have shown nighttime transportation noise to increase a number of biological risk factors, such as endothelial dysfunction, oxidative stress and blood pressure. Also, a disturb sleep is known to be associated with major diseases, such as cardiovascular disease and diabetes, and potentially also cancer.

Noise and cardiovascular diseases

Research in health effects of transportation noise has during the last decades focused on investigating the impact on cardiovascular disease. These studies have consistently found that exposure to traffic noise, from both road traffic and aircrafts,  increase risk of myocardial infarction, stroke and hypertension. Also, recent studies have suggested that traffic noise may also be a risk factor for other cardiovascular diseases, such as atrial fibrillation and heart failure.
For occupational noise, focus has also been on effects on the cardiovascular system. A review of occupational noise exposure and hypertension indicated a significant increase in blood pressure among workers with high vs. low exposure. Occupational noise has also been associated with coronary heart disease and stroke, although associations with these diseases are less investigated and consistent. Only one Swedish study analyzed the joint exposure of residential transportation noise and occupational noise when investigating effects on cardiovascular disease. The study indicated that a combination of the two noise exposures, together with stress at work, led to a particularly high risk of myocardial infarction, but the study needs reproduction in more and larger studies.

Noise and diabetes

In recent years, studies have found transportation noise to be associated with other major diseases, suggesting an etiological role of noise in diseases of great public health significance, also besides cardiovascular disease. This includes diabetes, which is one of the largest public health challenges today, with more than 400 million people affected worldwide. Potential mechanisms behind an effect of noise on diabetes, include reduced insulin levels and sensitivity due to increased levels of cortisol and disturbance of sleep, as well as changed levels of appetite-regulating hormones due to sleep disturbance. Long-term exposure to residential road traffic noise has been found to significantly increase the risk of diabetes. This is supported by a number of studies showing both aircraft and road traffic noise to be associated with obesity and higher levels of fasting glucose.

Noise and cancer

A few studies have shown that transportation noise may also be a risk factor for development of cancer, including breast and colon cancer and non-Hodgkin’s lymphoma. Noise may affect the carcinogenesis through suppression of melatonin, which is known to have various anti-carcinogenic properties, as well as by effects of stress and sleep disturbance on the immune system.

Noise and lifestyle

Furthermore, a number of studies have found an association between traffic noise and unfavorable lifestyle, including being physically inactive, smoking and consuming more alcohol. These lifestyle-factors are well-known risk-factors for both cardiovascular disease, diabetes and cancer.

Noise during pregnancy

A few recent studies have indicated that exposure to noise during pregnancy may have adverse effects on the fetus, e.g. low birth weight, as well as the mother, e.g. pre-eclampsia and pregnancy-induced hypertension. Potential mechanisms are maternal sleep disturbance and stress, which may increase heart rate and stress hormone levels, and elevate blood pressure. High maternal cortisol levels may reduce fetal growth, and hypertension is associated with small-for-gestational age. From 20 weeks of gestation, the fetus can produce an independent stress response to external stimuli, which may further restrict growth. A recent Swedish study found an association between occupational noise exposure during pregnancy and hearing dysfunction in children, indicating that sound is transmitted from the air over the abdominal wall and affects the uterus. These effects are of significant concern because the health status at the time of birth may affect the whole life-course of an individual, which highlights the need for more research within this area.

Noise and socioeconomic position

Socioeconomic inequalities are associated with unequal exposure to environmental risk factors. These factors contribute to health inequities and most often put disadvantaged groups at significantly higher risk for environmental health effects. Only a few studies have examined the associations between exposure to noise and socioeconomic position. Some studies on noise and self-reported noise exposure and annoyance found income and poverty-related inequalities in traffic noise exposure. For objectively assessed noise exposure, a few studies have investigated the association between socioeconomic position and traffic noise exposure, but results are inconsistent. This highlights the need to study patterns of environmental inequalities across various economic, social and cultural contexts.