Evidence of noise’s physiological effects—whether on cells and organs or entire populations—“is really coming together and painting a picture of the problem,” says Mathias Basner, a psychiatrist and epidemiologist at the University of Pennsylvania and president of the International Commission on the Biological Effects of Noise. Yet, he adds, few people are aware of the severity of what his colleagues call a “silent killer.”
Estimates suggest that roughly a third of Americans are regularly exposed to unhealthy levels of noise, typically defined as starting around 70 to 80 decibels. For comparison, normal conversation is about 60 dB, cars and trucks range from 70 to 90 dB, and sirens and airplanes can reach 120 dB or more.
Numerous studies link chronic exposure to environmental noise to an increased risk of heart-related troubles. People living near the Frankfurt airport, for example, have as much as a 7 percent higher risk of stroke than those living in similar but quieter neighborhoods, according to a 2018 study in Noise & Health that investigated the health data of more than 1 million people. An analysis of nearly 25,000 cardiovascular deaths between 2000 and 2015 among people living near Zurich’s airport saw significant increases in nighttime mortality after airplane flyovers, especially among women, a team reported last year in the European Heart Journal.
As researchers probe the physiology underlying noise’s cardiovascular consequences, they’re zeroing in on a culprit: dramatic changes to the endothelium, the inner lining of arteries and blood vessels. This lining can go from a healthy state to one that’s “activated,” and inflamed, with potentially serious ramifications.
When sound reaches the brain, it activates two important regions: the auditory cortex, which interprets noise, and the amygdala, which manages emotional responses to it. As noise gets louder, and especially during sleep, the amygdala activates a stress response—even if the person isn’t aware of it.
Once initiated, this response releases hormones such as adrenaline and cortisol into the body. Some arteries constrict; others dilate. Blood pressure rises, and sugars and fats flood the bloodstream for quick use by the muscles. The cascading stress response also prompts the creation of harmful molecules that cause oxidative stress and inflammation in the lining of blood vessels. This dysfunctional endothelium meddles with blood flow and affects numerous other processes that, when impaired, contribute to a range of cardiovascular illnesses, including high blood pressure, plaque buildup in arteries, obesity, and diabetes.
Studies on people and mice show that the endothelium doesn’t work as efficiently after just a few days of nighttime airplane-noise exposure, suggesting that loud noise isn’t a concern only for people already at risk for heart and metabolic problems. Healthy adults subjected to recordings of trains during their slumber had impaired blood-vessel function almost immediately, according to a 2019 study published by Münzel and his colleagues in Basic Research in Cardiology.