When a couple is trying to conceive, fertility can seem like a vague, confusing concept — what makes someone more or less fertile? And how might all of the different body systems contribute to that fertility level? A new study, published Feb. 21st in Frontiers in Genetics, connects men’s fertility, or in some cases, infertility, to something they might not have expected — their chronotype. (1)
The 2023 study found that chronotype, or the time of day you feel most awake or sleepy, affects testosterone levels in men. By analyzing published data of more than 500,000 people across the U.K., the study discovered that there is a link between one’s predisposed genetic chronotype and bioavailable testosterone levels. The authors of this study believe that it is the first of its kind to explore the connection between sleep traits and fertility at the genetic level.
The study gives medical providers another avenue to help those suffering from male infertility to look at their sleep health. Some might not realize how intertwined reproductive health, including hormone levels, and sleep actually is.
Chronotypes are impacted by genetics and the circadian rhythm, and while they can evolve as you age, they typically aren’t something you can change (which is how they differ from the circadian rhythm). There are four common chronotypes, based on their specific characteristics as it relates to productivity and bedtime, including:
- The Lion: Early risers
- The Bear: Sleep and wake with the sun
- The Wolf: Night owls
- The Dolphin: Light sleepers
The researchers suggest a connection for multiple reasons, such as the fact that sleep deprivation during the second half of the night has been shown to “significantly lower” testosterone levels in the morning. In addition, sleep issues sometimes go hand in hand with increased stress hormones, such as cortisol, which they say can decrease testosterone production. The researchers don’t go so far as to connect certain chronotypes above with definitively higher or lower fertility, though. Instead, they recommend child-bearing aged men pay attention to sleep according to their biological clock to reduce the risk of infertility.
The relationship between sleep and hormones has been studied for many years. In addition to this study, a 2021 study found that men who get at least eight hours of sleep were four times more likely to have healthy sperm than those who got seven or fewer hours of sleep at night.
Also, an older 2017 study found that men typically have later chronotypes than women until the age of 40 (2). After that, their chronotype can shift and they become an earlier chronotype than women. A 2024 study found that males often are later chronotypes, which leads to poorer cardiorespiratory health and an increased risk of metabolic diseases. (3)
So, while you might pride yourself on being that night owl or early riser, it might be wiser to prioritize high-quality sleep, and enough of it, as a lesser-known way to optimize your chances of conceiving.
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Sources
1. Shikuan, Lu; Ziyang, Ma; Wanzhen, Zhou; Hongsen, Zeng; Jian, Ma; Hang, Deng; Peihai Zhang; “Association of sleep traits with male fertility: a two-sample Mendelian randomization study,” Frontiers in Genetics; Volume 15 – 2024 | https://doi.org/10.3389/fgene.2024.1353438; February 21, 2024.
2. Dorothee Fischer, David A. Lombardi, Helen Marucci-Wellman, Till Roenneberg; ”
Chronotypes in the US – Influence of age and sex,” PLOS1;
https://doi.org/10.1371/journal.pone.0178782; June 21, 20173. J. Matthew Thomas, Philip A. Kern, Heather M. Bush, Sarah J. Robbins, W. Scott Black, Julie S. Pendergast, Jody L. Clasey; “Exploring the role of sex in the association of late chronotype on cardiorespiratory fitness,” The Physiological Society; https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15924
