In overweight and obese men, higher testosterone levels are associated with poorer sleep quality, according to a new study whose results were presented Monday at the joint meeting of the International Society of Endocrinology and the Endocrine Society: ICE/ENDO 2014 in Chicago.

“This finding could have clinical relevance in the context of the recent increase in testosterone prescriptions in middle-aged men, as poor sleep quality has been linked to increased risk of diabetes and hypertension,” says Eve Van Cauter, PhD, the study’s senior investigator, in a release. She is director of the University of Chicago Sleep, Metabolism and Health Center, where the study took place.

With three of four US men now overweight or obese, the researchers wanted to determine which factors influence sleep quality in this population. Overweight and older age can contribute to obstructive sleep apnea (OSA).

The research team performed a polysomnogram in 44 men ages 20 to 50 years who were overweight or obese. All subjects were otherwise healthy and were nonsmokers. Their selection for the study did not consider whether they had symptoms or a history of sleep apnea, according to Van Cauter. However, the sleep study showed that 29 (66%) of the men did have OSA, which she said was moderately severe in most cases.

In addition to apnea episodes, the sleep study evaluated the brain’s slow-wave activity during non-rapid eye movement sleep, which is a marker of sleep depth. Low slow-wave activity indicates shallow sleep, which causes a person to wake up easily and feel unrested after a night of sleep.

The morning after the sleep study, the men gave blood samples for measurement of their total testosterone level.

To explore the factors associated with slow-wave activity, the researchers performed statistical analyses (using multivariate regression) that first included only subjects’ demographic characteristics. Older age and African-American race predicted low slow-wave activity, or shallow sleep, the data showed. Body mass index, a measure of height and weight, had no significant effect on slow-wave activity.

Later analyses demonstrated that higher total testosterone level strongly correlated with more shallow sleep. This association, Van Cauter says, was independent from the presence of other factors known to decrease sleep quality, such as age, race/ethnicity, and OSA severity.

Because doctors are increasingly prescribing testosterone replacement therapy for middle-aged and older men with low testosterone levels, Van Cauter says, “Further studies are needed to clarify the impact of testosterone replacement on sleep quality, especially sleep depth.”

Study funding sources were the National Institutes of Health, the ResMed Foundation, and a grant from the Brussels Institute for Research and Innovation.