For men under the age of 65, a good night's sleep may have just been promoted from a “nice to have” to a “need to have.” Investigators believe they have found a link between disrupted circadian rhythms and a greater risk of prostate cancer.

The scientists examined data from the Cancer Prevention Study-I (CPS-I) and Cancer Prevention Study-II (CPS-II), two studies done by the American Cancer Society that followed close to a half-million men each. CPS-I ran from 1950 through 1972; the later survey was from 1982 through 2012.

The researchers discovered that during the first eight years of follow-up, among men under the age of 65, subjects who got 3 to 5 hours of sleep per night had a 55 percent greater risk of dying of prostate cancer than men who enjoyed 7 hours of sleep per night. Men who got 6 hours of sleep per night had a 29 percent higher risk than those who received seven hours. For men 65 years or older, however, it was a wash: they showed no increases or reduction in their risk of death from prostate cancer, no matter how much sleep they got.

What's the science? Nobody is certain yet. One theory favored by Susan M. Gapstur, PhD, MPH, who lead the study has to do with the sleep-inducing hormone melatonin. Low melatonin production – a condition sparked by insufficient sleep – can cause increased genetic mutations, greater oxidative damage, reduced DNA repair, immune suppression and dis-regulation of a number of genes involved in the suppression of tumors.

Unfortunately for that theory, none of the explanations account for the apparent lack of association between sleep deprivation and death from prostate cancer in men over 65. Gapstur suggests that it might be related to the natural decline in night-time melatonin levels with age, offering that this might reduce 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.”

The research was presented at the American Association for Cancer Research Annual Meeting 2017.