SEMEN SAMPLES

Sperm quality found highest in samples provided around lunchtime

Published 28 June 2022

An analysis of more than 30,000 semen samples collected at a China sperm bank found variations in sperm parameters according to the time of day, with best results in samples collected between 11.00 and 15.00; these results were replicated in a strictly controlled in vivo study.

A remarkable study from China has analysed more than 30,000 semen samples collected at different times of day between 2010 and 2015 and found ‘substantial diurnal oscillations’ in quality, with most sperm parameters reaching a peak between 11.00 and 15.00.(1) ‘The findings,’ say the authors, ‘could help us to estimate semen quality more precisely and to obtain higher quality sperm for use in ART and in natural conception.’

The results were reliably derived from comparing the medical records of samples taken at a sperm bank with those of a small in vivo study which collected sperm samples from six volunteers at six time points with identical time intervals (2 days plus 4 hours) and controlled periods of abstinence. In this way, say the authors, ‘the sperm bank study with a large sample size and the in vivo study with a strictly controlled abstinence period in a 24-h time window could be compared to describe the diurnal rhythms in human semen parameters’. This comparison showed that the temporal variation of semen parameters found in the sperm bank was indeed replicated in the laboratory study.

The abstinence period – as strictly controlled in the in vivo study – was described as a ‘vital determinant’ of semen parameters, thought to correlate closely with the time point of semen collection; most former studies have defined abstinence according to days, not hours, and has been usually based on memory. As a result, the authors note, it is not clear to what extent this crude estimation of abstinence would bias any previous analysis of diurnal rhythms in semen parameters.

This is not the first study to find variations in sperm parameters in samples provided by the same subject. However, the origin and reasons for these variations have remained unclear – and diurnal rhythm, the study now suggests, might be an ‘important cause’.

Results from the sperm bank analysis firstly showed a statistically significant time-dependent variation in total sperm count, sperm concentration, semen volume, progressive motility and total motility (all p <0.001) throughout the daytime hours of collection. Such was the variation that each hour earlier/later than 11.00 was associated with 1.14-fold risk of ineligibility. For example, total sperm count at 11.00 was 12.1 million more than found at 17.00. The study also showed that results from sperm DNA fragmentation tests reached their lowest level at around 11.00.

Why should the time of day affect the parameters of human semen? The authors suggest that the oscillations in sperm viability they saw in their study reflect mating patterns seen in other species. They cite the case of the gypsy moth, whose mating generally occurs in darkness when the sperm are released from testis to seminal vesicles according to a circadian clock. Men, however, are not moths, and the authors helpfully remind us that ‘human intercourse most often takes place at night’ – despite the apparent paradox of sperm quality. Is night-time conception attempt, they ask, an evolutionary habit which has not yet worked its way into semen quality?

Meanwhile, the more general findings of the study showed that only a minority of volunteers (15-30%) actually met the sperm bank’s eligibility requirements, usually because of inadequate sperm count and motility. And presently, they note, such figures reflect a serious challenge to fertility centres – even as demand for donor sperm continues to grow. The results of this study, they thus propose, suggest that ‘ejaculating at “optimal” time points could be a novel way to obtain more sperm without the decrease in progressive motility’ - and this may also be helpful to boost the chance of natural conception.


1. Liu K, Meng T, Chen Q, et al. Diurnal rhythm of human semen quality: analysis of large-scale human sperm bank data and timing-controlled laboratory study. Hum Reprod 2022; doi.org/10.1093/humrep/deac135

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