A good night’s sleep may help couples struggling to conceive, suggests new research presented this week at the American Society for Reproductive Medicine’s annual conference held in Salt Lake City, Utah.

Researchers examined data from a previous population study of couples planning to get pregnant, the Boston University Pregnancy Online Study (PRESTO). Looking at 695 couples who had been trying to conceive for the past six menstrual cycles or less, the researchers found that the men’s quality and length of sleep was associated with the chances of successful conception. Men who reported regularly sleeping either less or more than 6 to 8 hours of sleep were noticeably less likely to impregnate their partners, as were men who reported having trouble sleeping at least some of the time. The success rate lowered the worse sleep the men got, and the relationship held firm even after accounting for other factors like a history of depression, body mass index, or frequency of sex.

"There is very little data about how men's sleep may affect fertility," Dr. Peter Schlegel, an urologist unaffiliated with the study, told HealthDay. "We know any stress can affect fertility for both women and men. This study strongly suggests that for men, aiming for the 7 to [less than] 9 hours of sleep helps to optimize their fertility and their chances of contributing to a pregnancy."

Schlegel is vice president of the American Society for Reproductive Medicine, as well as chief of urology at New York City’s Weill Cornell Medicine.

Men who regularly slept less than 6 hours or 9 hours were 42 percent less likely to conceive with their partners within any given month compared to those who got 8 hours of sleep, explained lead author Dr. Lauren Wise, a professor of epidemiology at Boston University School of Public Health. And the results were similar for couples who had only been trying to conceive for three menstrual cycles or less as well.

As for why, Wise noted that sleep helps regulate men’s daily testosterone levels, which in turn promote good sperm quality. Elsewhere, other research has found that sleep problems are associated with lower sperm concentration, total sperm count, and level of healthy sperm, the authors said, along with lower testosterone.

Like all studies of its kind, the findings only point to a possible link between sleep and male fertility, and don't support a direct cause-and-effect relationship. Additionally, the preliminary study has not yet been published in a scientific journal, meaning it hasn’t still undergone peer-review. Wise and her colleagues hope that more research can shine a light on how sleep affects fertility.

Source: Wise L, Mckinnon C, Wesselink A, et al. Sleep And Male Fecundity In A North American Preconception Cohort Study. American Society for Reproductive Medicine Scientific Congress. 2016.