Gestational diabetes mellitus (GDM) is a form of diabetes that affects pregnant women. Usually it resolves after delivery, but it still continues to have an impact on the mother and her child. Affected women are seven times more likely to exhibit abnormal glucose intolerance in later life. Meanwhile, children born to mothers with GDM have a higher risk of obesity.

Previous studies have shown a link between noise exposure and another form of diabetes: type 2 diabetes mellitus. As a result, Kyoung-Bok Min and Jin-Young Min, both from the Seoul National University in the Republic of Korea, were interested to see if there was any link between noise pollution and GDM.

Korea has a compulsory social insurance programme known as the National Health Insurance Service (NHIS), which covers the entire population. Using the NHIS database, the scientists randomly selected 1,025,340 subjects (2.2% of the eligible population) who had records throughout the period 2002 to 2013. The researchers then whittled this sample down to the 18,165 women who were pregnant during this period and who didn't have pre-existing diabetes. Via the National Noise Information System, Min and Min were able to obtain average daytime and night-time noise levels for each of the study subjects.

During the study period 8.8% of the women developed GDM during their first trimester of pregnancy. After adjusting for other known risk factors, including a family history of diabetes, increased maternal age, obesity, non-white ethnicity, lack of physical activity and cigarette smoking, the scientists found that there was a clear increase in risk of developing GDM for women exposed to above average levels of noise at night.

The researchers show that the odds of developing GDM during the first trimester are 1.6 times higher for pregnant women exposed to elevated night-time noise, compared to similar women exposed to baseline levels of night-time noise in South Korea. Meanwhile, there was no significant correlation between increased exposure to daytime noise and the risk of developing GDM.

Exactly why exposure to noise at night increases the risk of GDM is not clear. However, previous studies have shown that increased noise exposure is often linked with a significant increase in stress hormones including corticosterone, cortisol and catecholamine.

"Exposures to chronic and high levels of night-time noise could stimulate secretion of stress hormones and could induce sleep disturbance, which can further impair endocrine and metabolic parameters including insulin and glucose metabolism," Min and Min write in their paper in Environmental Research Letters (ERL) .

Night-time noise levels in cities in South Korea are generally higher than average, but Min and Min don't believe that the problem is confined to South Korea. Even in quieter cities in other countries the noise at night is likely to be enough to raise the risk of GDM significantly.

The study adds further weight to the growing body of evidence that excessive noise is bad for our health. Fortunately, this is a problem that can be tackled, for example by using noise regulations for residential areas, improvements to noise insulation in housing, and encouraging low-noise vehicles.

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