Men, take note: A quiet bedroom might make for strong, healthy sperm.
South Korean researchers found that men who slept where the noise level routinely exceeded that of a suburban neighbourhood had worse fertility than men who rested in quieter quarters.
The study, by Kyoung-Bok Min and Jin-Young Min, was published in the journal Environmental Pollution.
"I think any sort of stressor can contribute to infertility... and I would say bedroom noise can be a chronic stressor in sleep," said Dr James Nodler. He's a reproductive endocrinology and infertility specialist at Houston Methodist Hospital.
"It's basically a protective feature by our bodies – if we're under severe stress, now is not the time to reproduce," added Nodler, who wasn't involved in the new research.
About 15% of American couples are unable to conceive after a year of unprotected sex, according to the US National Institutes of Health. Factors contributing to infertility in either sex are wide-ranging; in men, they include problems with sperm concentration, movement or shape.
About 15% of South African couples experience fertility problems.
A previous Health24 article added decreasing processed-meat consumption, stopping smoking, decreasing alcohol consumption and losing weight to the list of recommendations to optimise male fertility outcomes.
A recent study in mice suggested that men might also face low testosterone levels and low sperm counts after Zika infection, affecting their fertility.
A similar association in women
In the research, scientists from Seoul National University analysed health insurance data on more than 206 000 men aged 20 to 59. Noise exposure levels were calculated by combining men's residential location (using postal codes) and information from a national noise information system.
In the eight years covered by the data, about 3 300 of the men had an infertility diagnosis. After adjusting the data for factors such as age, income, smoking and body mass index (BMI), the researchers found men were 14% more likely to be diagnosed with infertility if exposed to nighttime noise over 55 decibels. That's equivalent to the noise generated by an air conditioner or a suburban street.
Earlier research found a similar association in women, with noise levels linked to an increased risk for premature birth, miscarriage and birth defects, the study authors noted.
Nodler explained that chronic noise in the bedroom may disrupt the release of a hormone known as GnRH (gonadotropin-releasing hormone) in the brain, which triggers the release of other hormones important to fertility.
"This is biologically plausible to me," Nodler said. "If you disrupt GnRH, that throws the whole balance of fertility out of whack, both for men and women."
Good 'sleep hygiene' measures
Another US fertility expert cautioned that the new research doesn't establish a cause-and-effect relationship between noisy bedrooms and male infertility.
"It is possible that excessive exposure to high decibels is somehow associated with worsened semen [quality], but the study does not necessarily prove that prolonged noise exposure causes infertility," said Dr Jennifer Kawwass. She's medical director of IVF (in vitro fertilisation) and third party reproduction at Emory Reproductive Center in Atlanta.
To determine the exact biological reason for the link, Nodler said future research should measure hormone levels in men with noisier bedrooms compared to men with quieter bedrooms.
Nodler recommended that men concerned about their fertility keep noise levels down in the bedroom as well as practice good "sleep hygiene" measures. These include avoiding TV or any other screen time while in bed, he said.
"It's an interesting topic to think about, that just reducing bedroom noise [may enhance] fertility," Nodler added. "It's definitely biologically plausible and – for anyone – having less bedroom noise is better for general health and fertility."
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