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Short answer, the time of day men and sperm are most fertile is in the mornings from 11:00 a.m. to 12:00 p.m.
So does our circadian clock really influence sperm quality throughout the day?”
What evidence is there, and does it really matter?
Well, the first study by Cagnacci et al. (1999) actually reported significantly higher sperm count and concentration in the afternoon (5:00-5:30 p.m.) rather than the morning (7:00-7:30 a.m.). However, this was only a small preliminary study featuring 54 men and a flexible abstinence period of 3-4 days.
Following this study, another team of researchers, Biljan M et al. (2004), attempted to duplicate these results in a much larger group of men. This larger study involved 276 men and 570 semen samples, of which 289 were produced in the morning (8:00-9:00 a.m.) and 281 in the evening (7:00-8:00 p.m.). However, after statistical analysis of the results no statistically significant differences was reported between morning and evening semen samples. The lack of abstinence period data (and uncontrolled abstinence period) is most likely the reason for this finding (as you’ll see later on).
This result however stalled research on the topic for almost a decade until a rat study finally confirmed the influence of circadian rhythms on the reproductive system. Coincidentally genetic research in humans around this period began to link clock genes with semen quality and infertility.
In 2018 the results of a large retrospective study proved the original hypothesis beyond any doubt. Statistical analysis of 12245 semen samples from 7068 men clearly showed significantly higher sperm concentration, total sperm count and normal morphology among samples produced in the morning before 7:30 a.m. However, like previous studies, the flexible abstinence period still left the study open to questions among experts.
Thankfully Liu K, et al. (2022) put this question to bed in their own study. First, statistical analysis of 33430 semen samples retrospectively, from 8485 male donors, showed a peak sperm concentration and total sperm count in the mornings at 11:00 a.m., while peak progressive motility, total motility and semen volume occurred at 12:00 p.m. To confirm these results were true beyond any doubt, 6 healthy young males was then recruited to provide 7 semen samples each following a strictly controlled abstinence period of 52 hours. Analysis of these results confirmed peak sperm quality between 11:00 a.m. (second sample) to 3:00 p.m. (third sample) in the same order as reported earlier with sperm concentration and total sperm count peaking first followed by progressive motility and total motility a little later. Unsurprisingly sperm DNA damage (DFI, HDS) was also lowest at 11:00 a.m. as previously reported by Ni W, et al. 2019.
So how much does this really matter?
Short answer more than you would think. Liu K, et al. (2022) calculated that for each hour away from the ‘peak time’, the risk of producing an ineligible semen sample increased by 14%.
Talking in sperm parameters, this translates into potentially 36% lower total sperm count, 30% lower sperm concentration, 3.6% lower total motility, 4.8% lower progressive motility and 12% lower semen volume from peak to trough over 24 hours.
In short, this means for males with borderline semen quality timing ejaculation for some time between 11:00 a.m. and 12:00 p.m. is worth trying according to the science.
Liu K, et al. (2022). Diurnal rhythm of human semen quality: analysis of large-scale human sperm bank data and timing-controlled laboratory study. https://doi.org/10.1093/humrep/deac135
Ni W, et al. (2019). Diurnal variation in sperm DNA fragmentation: analysis of 11,382 semen samples from two populations and in vivo animal experiments. https://doi.org/10.1080/07420528.2019.1649275
Xie M, et al. (2018). Diurnal and seasonal changes in semen quality of men in subfertile partnerships. https://doi.org/10.1080/07420528.2018.1483942
Shen O, et al. (2015). Variants of the CLOCK gene affect the risk of idiopathic male infertility in the Han-Chinese population. https://doi.org/10.3109/07420528.2015.1056305
Qin F, et al. (2014). Circadian alterations of reproductive functional markers in male rats exposed to 1800 MHz radiofrequency field. https://doi.org/10.3109/07420528.2013.830622
Hodžić A, et al. (2013). Genetic variation in circadian rhythm genes CLOCK and ARNTL as risk factor for male infertility. https://doi.org/10.1371/journal.pone.0059220
Biljan M, et al. (2004). Absence of diurnal variation in semen parameters in normospermic men. https://doi.org/10.1016/j.fertnstert.2004.10.026
Cagnacci A, et al. (1999). Diurnal variation of semen quality in human males. https://doi.org/10.1093/humrep/14.1.106
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