Traffic noise raises the risk of central obesity, suggests a Swedish study that surveyed over 5,000 men and women, collecting information on decibels of exposure and markers of obesity.
Living near a busy road, railroad or under aircraft noise was associated with bigger waist sizes and waist-to-hip ratios, and there was a cumulative risk found for being exposed to all three noise factors in the study published in Occupational and Environmental Medicine, a journal from The BMJ.
The researchers assessed how much environmental noise pollution from road traffic, trains, and planes had been experienced by 5,075 people living in five suburban and rural areas around Stockholm - using official measures tied to where the respondents lived since 1999.
During assessments between 2002 and 2006, the respondents aged 43 to 66 answered questions on lifestyle, state of health, psychological distress, insomnia and strain in their jobs.
The participants also underwent a medical examination, which included measures of central body fat using waist circumference along with hip size. Overall levels of obesity were also measured by body mass index (BMI).
While the study found no association for living near the sources of noise against BMI, it did find a link against abdominal obesity, in these ways:
- There was an increase in waist size of 0.21 cm (0.08 in) for every 5 dB increase in noise exposure above 45 dB (noise was considered harmless below this threshold). This was a statistically significant trend for women but not men
- A stronger association for the males was found with the waist-to-hip ratio, which went up overall by 0.16 for every 5 dB rise in road traffic noise exposure
- Any of the three sources of noise correlated with a larger waist size, but the link was strongest for aircraft noise
- Only road traffic and aircraft noise were associated with the waist-to-hip ratio measure of central obesity.
The ratio of the chances of finding people with a big waist size among those exposed to only one of the three sources of noise, over the chances among those without any noise pollution, was 1.25. This odds ratio increased for people exposed to all three sources of noise, to an odds ratio of 1.95.
Just over half of all the participants (2,726 or 54%) had been exposed to one source of traffic noise above 45 dB, 15% (740) to two sources, and 2% (90) to all three sources.
The findings were not influenced by socioeconomic factors, lifestyle or exposure to ambient air pollution from local road traffic. But age was an influential factor, with associations between central obesity and road traffic noise found only for those below the age of 60.
Noise stress may be linked to central fat deposits by hormone effects
The study was not designed to establish any cause-and-effect relationship between the factors and outcomes observed. Its measures of noise exposure were based on location and did not take account of any sound insulation measures that might have been taken, nor of the location of the participants' bedrooms.
The authors do propose why noise exposure could be an important physiological stressor, however.
They suggest high levels of noise pollution could result in higher levels of the hormone cortisol, which are thought to have a role in fat deposition around the middle of the body.
"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."
Traffic noise may also affect metabolic as well as cardiovascular functions, through sleep disturbance, the researchers also suggest, altering appetite control and use of energy.