London, May 26 (IANS): Living near an airport, highway or train station could increase your risk of developing a mid-riff bulge, indicates a new research.

Exposure to a combination of road traffic, rail, and aircraft noise may pose the greatest risk of acquiring a spare tyre -- otherwise known as central obesity, the researchers said.

Noise exposure may be an important physiological stressor and bump up the production of the hormone cortisol, high levels of which are thought to have a role in fat deposition around the middle of the body, the study said.

"This may explain why the effects of noise were mainly seen for markers of central obesity, such as waist circumference and waist-hip ratio, rather than for generalised obesity, measured by BMI (Body Mass Index)," the study said.

The researchers assessed how much road traffic, rail, and aircraft noise 5,075 people living in five suburban and rural areas around Stockholm, Sweden, had been exposed to since 1999.

They did this by using official figures on road and rail traffic noise levels and flow.

Between 2002 and 2006, when they were aged between 43 and 66, they completed a detailed questionnaire covering lifestyle, current state of health, levels of psychological distress, insomnia and job strain.

The researchers found no link between road traffic noise and BMI. But there was an association between road traffic noise and waist size, with a 0.21 cm increase for every additional five decibel (dB) increase in exposure, although this was only significant among women.

Similarly, there was a link to waist:hip ratio, with a change of 0.16 for every five dB increase in noise exposure to road traffic. This association was stronger in men.

A larger waist was significantly associated with exposure to any of the three sources of noise, but the link was strongest for aircraft noise; a larger waist:hip ratio was associated with road traffic and aircraft noise only.

The study was published online in the journal Occupational & Environmental Medicine.