Scientists pinpoint best time and season for sperm

The time at which a sperm sample is produced may influence its quality, according to a new study.

Researchers at the University Hospital of Zurich, Switzerland, analysed 12,245 semen samples from 7068 men, between 1994 and 2015. The researchers, led by Dr Min Xie, found that semen quality varied with the time of day and year that the sample was produced.

The samples were examined for sperm concentration, total sperm count, progressive motility and sperm shape. For healthy semen samples collected between 5:00am and 7:30am were found to exhibit a statistically higher sperm concentration, total sperm count and a higher percentage of normally shaped sperm, compared to samples produced later in the day. Sperm motility was not influenced by the time of sample production.

The 7468 samples that had abnormal characteristics showed a similar pattern. For these samples, sperm concentration was found to be highest when the sample was collected between 5:00am and 7:30am. Sperm movement was best in samples produced between 8:31am and 10:00am. Sperm shape was not influenced by the time of collection for these samples.

In addition to circadian variation, semen quality also varied by season. Sperm concentration and total sperm count were found to be significantly higher during the spring months and significantly lower during summer. There was no yearly variation in sperm motility, but a higher proportion of normally shaped sperm was observed in summertime samples.

The causes of the daily and seasonal variations are not conclusively known.

'The most likely cause for the circannual variation of semen quality is the effect of photoperiod, eg the length of daylight,' the authors write in the paper. Hormones such as melatonin, testosterone and cortisol, which exhibit their own circadian patterns of expression, could be responsible for the daytime fluctuations observed in semen quality, the authors hypothesise.

The semen samples included in the study were produced within a 12-hour window from 5:00am to 17:00pm. The authors acknowledge that they 'lack data on the (late) evening, when sexual activity is highest'. As a result, further research is required to achieve a full understanding of the circadian fluctuations of semen parameters.

However, the production of semen samples before 10:00am could 'be used to improve natural fertility as well as fertility resulting from assisted reproduction', they state, adding that timing sample collection is one of the few ways to improve semen quality.

The study is published in the journal Chronobiology International.