Mumbai: Loud noise is not only an irritant, it can also kill. Latest research from the western world says that for every 10 decibel increase in noise level, the risk of heart attack went up by 12&. The implication for Mumbai, which is known as one of the noisiest cities in the world, can only be imagined, said anti–noise pollution activist Sumaira Abdulali from NGO Awaaz. "It is time Indians recognized noise pollution as a health problem instead of an environmental issue," she said, adding that despite the World Health Organization linking noise pollution to health in 1985, the realization has been slow.

The latest study linking heart and noise comes from Denmark, where over 55,000 people between 50 and 64 years of age were studied from 1993 for over a decade. The analysis, which was published in PLOS ONE journal on June 20, showed that residential exposure to road traffic noise was significantly associated with myocardial infarction or heart attack.

While there are no similar studies in India, activists like Abdulali give out instances where noise has been a major health irritant. "I know a family where the woman suffered a heart attack immediately after a cracker burst loudly nearby," she said.

Heart surgeon Pawan Kumar from Nanavati Hospital, Juhu, said previous studies have estimated that noise pollution causes 4& of all heart attacks. Noise literally disrupts the body’s rhythm, thereby directly affecting the heart.

• Risk of heart attack went up by 12& for every 10 decibel rise in noise level
• Mumbai is one of the world’s noisiest cities, with pollution reaching 132 decibels
• Previous studies estimate noise pollution causes 4& of all heart attacks
• Noise pollution disturbs sleep patterns, affecting the heart
• Loud noise releases stress hormones, causing heart to beat faster
• Constant exposure to noise induces continuous stress

Loud noise induces release of stress hormones ADanish study has brought home the deadly effects of noise pollution, particularly in a cacophonous city like Mumbai. Cardiologist Ganesh Kumar from Hiranandani Hospital, Powai, said that noise pollution disturbs sleep patterns, which, in turn, affects the heart.

IIT–Bombay put up sound barriers along its campus wall in Powai immediately after a part of its land was taken over for a road–widening project. "This underlines the fact that traffic sounds are a menace to health," Dr Kumar said.

Dr Pawan Kumar of Nanavati hospital said loud noise causes release of stress hormones such as cortisol and adrenaline. "These hormones cause the heart to beat faster," he said. Among people who suffer from irregular heart beat or arrhythmia, loud noise of over 80 decibel can lead to loss of beats and a sudden cardiac arrest. "In some people, loud noise can cause the coronary artery to go into aspasm and induce a heart attack," said Dr Pawan Kumar, adding that traffic policemen would at the highest risk here.

"Any increase in stress hormones is good only for a small period. The problem arises when this stress is continuous," said Dr Ramakanta Panda of Asian Heart Institute in BKC. Constant exposure to noise induces continuous stress, which is bad for the heart, he said. The PLOS One study said that "noise is known to affect the hypothalamus–pituitary–adrenal axis, leading to increased levels of cortisol". In addition, exposure to noise during the night at normal urban levels has been associated with sleep disturbances, which might affect metabolic and endocrine function and impair the immune system, the study added.