Traffic noise may increase risk of belly fat

People exposed to high levels of traffic noise may have an increased risk of abdominal obesity.

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People living near high-traffic areas may have a higher risk of developing extra fat around their midsection, according to a recent study.

The findings, published in the online journal Occupational & Environmental Medicine, suggest that people whose homes are near high-traffic roadways, rail lines, and airports are at the greatest risk for developing a spare tire, clinically referred to as central obesity, thought to be one of the most harmful types of body fat. The more sources of noise people were exposed to, the higher the risk of abdominal obesity.

"Exposure to traffic noise is increasing because of ongoing urbanization and increasing traffic volumes," study author Goran Pershagen told CBS News. "It is important to fully assess the public health consequences of this development."

Researchers calculated how much road traffic, railroad and aircraft noise 5,075 people in Sweden had been exposed to since 1999 by collecting official figures on traffic levels and flow from five municipalities and national data on aircraft noise from a major airport.

All of the people surveyed were part of the Stockholm Diabetes Prevention Program, which aimed to look at risk factors for the onset of diabetes and how best to prevent it. The participants, aged 43 to 66, completed detailed questionnaires, covering lifestyle, current state of health, levels of psychological distress, insomnia, and job strain. They were also asked about environmental noise pollution from road traffic, trains, and planes. Finally, the participants underwent a physical, including a blood pressure check, a test for diabetes, and measures of central body fat and overall obesity determined by body mass index (BMI).

The researchers found that 62 percent of the study subjects had been regularly exposed to road traffic noise of at least 45 decibels (dB), while one in 20 people had been exposed to similar noise levels from trains. Just over 1,100 participants had been exposed to aircraft noise of more than 45 dB.

While there was no link between traffic noise and overall BMI, the results suggest an association between this type of noise pollution and a larger waist size. There was a 0.21 cm increase in waist size for every additional 5 dB increase in noise exposure, most notably among women.

Similarly there was a slight increase in the waist-to-hip ratio for every 5 dB increase in noise exposure to road traffic, expressed more strongly in men.

The more sources of noise pollution people were exposed to at the same time, the greater their risk of a higher concentration of belly fat. Those exposed to only one source of noise had a 25 percent greater risk of having a larger waist, while those exposed to all three sources saw their risk almost double.

Though the researchers could not draw any conclusions about cause and effect, they suggest the connection may be due to noise pollution acting as a physiological stressor that elevates the production of the hormone cortisol. "Several studies show that such types of stress reactions are related to increased abdominal obesity," Pershagen said. He also suggests that noise may contribute to sleep disturbances affecting a person's metabolism, and thereby altering appetite and energy levels.

Dr. Hal Strelnick, division chief of Community Health in the Department of Family and Social Medicine at Montefiore Medical Center in New York City, said that although the study has many limitations, including the use of estimated noise exposures and a sample with an elevated diabetes risk, it is still an important finding.

"Most of the harms we look at from noise pollution involve damage to hearing," he told CBS News. "This study highlights that noise is ubiquitous and there may be other, more subtle long-term effects that we haven't been paying attention to. But the study just can't stand alone on that. It begs for more rigorous studies to tell us whether it is causative or just an association."

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    Ashley Welch covers health and wellness for CBSNews.com