Why chronic noise is not just annoying... it is a serious health threat

A growing body of research shows that chronic noise is not just annoying. It is a largely unrecognised health threat that is increasing the risk of high blood pressure, stroke and heart attacks worldwide.

We’ve all been told to limit the volume on our headphones to protect our hearing. But it is the relentless din of daily life in some places that can have lasting effects throughout the body.

Anyone who lives in a noisy area may feel they have adapted to the cacophony. But data shows the opposite – prior noise exposure primes the body to overreact, amplifying the negative effects. Even people who live in relatively peaceful rural communities can be at risk.

Effects on the body

A siren shrills. A dog barks. Engines thrum. Jackhammers clack.

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Unpleasant noise enters your body through your ears, but it is relayed to the stress detection centre in your brain. This area, called the amygdala, sets off a cascade of reactions in your body. If the amygdala is chronically overactivated by noise, the reactions begin to produce harmful effects.

The endocrine system can overreact, causing too much cortisol, adrenaline and other chemicals to course through the body. The sympathetic nervous system can also become hyperactivated, quickening the heart rate, raising blood pressure and triggering the production of inflammatory cells. Over time, these changes can lead to inflammation, high blood pressure and plaque build-up in arteries, increasing the risk of heart disease, heart attacks and stroke.

When researchers analysed the brain scans and health records of hundreds of people at Massachusetts General Hospital, they made a stunning discovery: those who lived in areas with high levels of transportation noise were more likely to have highly activated amygdalae, arterial inflammation and – within five years – major cardiac events.

The associations remained even after researchers adjusted for other environmental and behavioural factors that could contribute to poor cardiac health, such as air pollution, socioeconomic factors and smoking. In fact, noise may trigger immediate heart attacks: higher levels of aircraft noise exposure in the two hours preceding night-time deaths have been tied to heart-related mortality.

What is too loud?

Sound is often measured on a scale of decibels, or dB, in which near total silence is zero dB and a firecracker exploding within a metre of the listener is about 140 dB.

Compared with a quiet room, a passing freight train peaks at about four times as many decibels. But the difference in how loud the train sounds to the ear is much more dramatic: the train sounds more than 500 times as noisy.

That’s because the decibel scale is logarithmic, not linear. With every 10 dB increase, the sense of loudness to the ear generally doubles. And that means regular exposure to even a few more decibels of noise above moderate levels can set off reactions that are harmful to health.

According to the World Health Organisation, average road traffic noise above 53 dB or average aircraft noise exposure above about 45 dB are associated with adverse health effects.

Mounting research suggests that the relationship between noise and disease is eerily consistent. A study following more than four million people for more than a decade, for example, found that, starting at just 35 dB, the risk of dying from cardiovascular disease increased by 2.9 per cent for every 10 dB increase in exposure to traffic noise.

Scientists believe that pronounced fluctuations in noise levels might compound the effects on the body. They suspect jarring sounds that break through the ambience – recurring jet engines, a pulsating leaf blower or the brassy whistle of trains – are more detrimental to health than the continuous whirring of a busy roadway, even if the average decibel levels are comparable.

Swiss researchers measured and compared transportation noise along a highway with a railroad track, over the course of a night. They found that the highway and the railroad had the same average decibel level over the eight-hour night. But while the hum of the highway remained relatively steady throughout the night, the periodic passing of trains caused far more dramatic variation, a sound quality linked to harm.

In a subsequent Swiss study, higher degrees of night-time “noise intermittency” – or the extent to which sound events were distinguishable from the background levels – were associated with heart disease, heart attacks, heart failure and strokes.