New research suggests living near a road which is noisy at night-time may contribute to male infertility.
'We know noise exposure has an effect on male fertility in animals, but our study is the first to show the risk of exposure to environmental noise on male infertility in humans,' said study author Dr Jin-Young Min, from Seoul National University in the Republic of Korea.
Environmental pollutants, including noise, have been implicated in fertility difficulties before: observational studies suggest that noise may increase women's risk of birth complications including low birth weight infants, congenital malformations, preterm birth and miscarriage. In animal studies, noise has been shown to disrupt the balance of reproductive hormones in males, but little research has been performed in men so far.
The new study followed 206,492 healthy Korean men aged 20 to 59 for up to eight years. Infertility was diagnosed using medical history, genital examination and semen analysis. Exposure noise was estimated using data from monitors located across busy city areas; measurements were extrapolated to each individual's postcode.
During the study, 3293 men (1.6 percent) were diagnosed with infertility. The risk of infertility was found to be greater in men exposed to more than to 55 decibels (dB) of nocturnal noise – similar to that of a suburban street, or an air conditioner. This is the World Health Organisation's recommended limit of long-term night-time noise in Europe.
The increased risk was shown after taking into account exposure to air pollution, and other possible confounding factors such as age, lifestyle and disease history.
Small increases in noise - in 1 dB increments showed no significant effect on fertility, according to the study that was published in Environmental Pollution.
A limitation of the study is the estimation of noise levels at participants' residences by interpolating between noise monitors located in other inner city areas, acknowledge the researchers. They add that as a consequence they may have overestimated noise exposure and therefore infertility risk, compared with similar studies.