Shorter sleep duration was associated with increased risk of death from prostate cancer in men under the age of 65, according to data presented at the American Association for Cancer Research Annual Meeting 2017, April 1-5.

“There is growing interest in determining the potential health effects of factors that disrupt circadian rhythms, such as shift work and lack of sleep,” says the study’s lead author, Susan M. Gapstur, PhD, MPH, vice president of epidemiology at the American Cancer Society in Atlanta, in a release. Previous research has suggested an association between shorter sleep duration and fatal prostate cancer; this study sought to further examine this association.

Gapstur and colleagues analyzed data from the Cancer Prevention Study-I (CPS-I) and Cancer Prevention Study-II (CPS-II), two large, long-term cohort studies of the American Cancer Society. In all, the analysis included 407,649 men from CPS-I, followed from 1950 through 1972, and 416,040 men from CPS-II followed from 1982 through 2012. The study participants had self-reported numerous sleep-related behaviors, including sleep duration, shift work, and insomnia. All men were cancer-free at baseline. During the follow-up periods, 1,546 men in CPS-I and 8,704 men in CPS-II died of prostate cancer.

The researchers analyzed sleep duration in relation to deaths from prostate cancer, and found that during the first eight years of follow-up, among men under the age of 65, men who got 3 to 5 hours of sleep per night had a 55% greater risk of dying of prostate cancer than men who got 7 hours of sleep per night. Men who got 6 hours of sleep per night had a 29% higher risk than those who got seven hours.

Men who were 65 or older showed no difference in the risk of death from prostate cancer, no matter how much sleep they got.

Gapstur explains that while the specific biological mechanism is unclear, sleep deprivation and the associated presence of light at night can inhibit the production of melatonin, a hormone that affects sleep cycles. In turn, low melatonin production can spark increased genetic mutations, greater oxidative damage, reduced DNA repair, and immune suppression. Short sleep duration may also contribute to the disregulation of a number of genes involved in tumor suppression, she says.

Gapstur says that the reasons for a lack of association between sleep deprivation and death from prostate cancer in older men is unclear, but might be related to the natural decline in nocturnal melatonin levels with age, possibly reducing the relative impact of sleep deprivation.

“While these results are intriguing, and contribute to a growing body of evidence that circadian rhythm-related factors might play a role in prostate carcinogenesis, more research is needed to better understand the biologic mechanisms,” Gapstur says. “If confirmed in other studies, these findings would contribute to evidence suggesting the importance of obtaining adequate sleep for better health.”

Gapstur says limitations of the study include the self-reporting of data and the fact that data were collected only once, at the start of the study, and may, therefore, not reflect changes in sleep habits.

This study was funded by the American Cancer Society. Gapstur declares no conflicts of interest.