A new study found a link between sleep duration and a measure of chromosomal health in sperm. The findings are published in the Journal of Sleep Research.

In the study of 2020 semen samples provided by 796 male volunteers from colleges in Chongqing (China) from 2013 to 2015, volunteers with more than 9 hours per day of sleep and those with 6.5 hours or less per day sleep had 41% and 30% lower High DNA Stainability–an index that represents the proportion of sperm with abnormal chromatin–than did volunteers with 7 to 7.5 hours per day of sleep. Chromatin is a complex of DNA and proteins that forms chromosomes.

A 2016 study on sleep duration said Singaporeans sleep just slightly more than seven hours day, the least number of hours among places surveyed.

Singaporeans were also among those with the latest bedtime of 11.45pm, even as most of them woke up at about 7.10am. Singapore’s results match a similar study by SingHealth Polyclinics last year, which found that four in 10 people, or 44 per cent, lack sleep on weekdays.

The World Health Organisation (WHO) data over the years shows that general semen quality is getting poorer globally. The sperm quality of Singapore men is lags far behind international standards said a report by a Chinese Daily.

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The report said that healthy sperm have head shapes that are pointed which allows sperm to penetrate the eggs’ outer surface more easily. However, the sperm of a large segment of men in Singapore have heads that are more commonly round or oval in shape.

“This is new information after our previous finding that sleep duration has an inverse U-shaped association with semen volume and total sperm count. In the previous study, we found that these two semen parameters were highest when sleep is 7.0 to 7.5 hours per day, and either longer or shorter sleep was associated with the decrease of the two semen parameters,” said Dr Jia Cao, co-author of the study.