Susan M. Gapstur, PhD, MPH
Researchers from the American Cancer Society in Atlanta examined data from two large, long-term cohort studies, Cancer Prevention Study-I (CPS-I) and Cancer Prevention Study-II (CPS-II), and determined that shorter sleep duration was associated with an increased risk of death from the disease in men under age 65 years.
In the CPS-I study, 407,649 men were followed from 1950 through 1972 and 416,040 men from the CPS-II study were followed from 1982 through 2012. All men were cancer-free when the studies began. However, 1546 men in CPS-I and 8704 men in CPS-II died of prostate cancer during the follow-up periods.
Sleep-related behaviors such as sleep duration, shift work and insomnia were self-reported by study participants.
Examining the deaths from prostate cancer more closely, researchers found that during the first 8 years of follow-up, men younger than 65 who got 3-5 hours of sleep a night had a 55% greater risk of dying of prostate cancer than men who got 7 hours. In addition, men who got 6 hours of sleep a night had a 29% higher risk than those who got 7 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.
"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,” Susan M. Gapstur, PhD, MPH, vice president of epidemiology at the American Cancer Society and lead author on the study, said in a statement. “If confirmed in other studies, these findings would contribute to evidence suggesting the importance of obtaining adequate sleep for better health.”
Gapstur explained that sleep deprivation and the associated presence of light at night, such as the use of electronics like cell phones and televisions, can inhibit the production of melatonin — a hormone that affects sleep cycles. She added that producing low amounts of melatonin can cause increased genetic mutations, greater oxidative damage, reduced DNA repair and immune suppression. Also, less sleep may contribute to the dysregulation of genes involved in tumor suppression.
Regarding sleep duration and death from prostate cancer in older men, Gapstur said the reasons remain unclear. However, she feels it may be related to the natural decline in nocturnal melatonin levels with age, possibly reducing the relative impact of sleep deprivation.
The authors noted two limitations of the study: self-reporting of data and the fact that data were collected only once, at the start of the study.