In scientific circles Stevens is widely credited with being the first to articulate the hypothesis that the increasing use of artificial light at night may be related to the high breast cancer risk in the industrialized world.
Results show that higher sleep efficiency was significantly associated with lower mortality over the ensuing six years, an effect that remained after adjusting for baseline prognostic factors such as age, estrogen receptor status and treatments received. Mean survival was 68.9 months for efficient sleepers compared with 33.2 months for participants with poor sleep efficiency. Further analysis found that a 10 percent increase in sleep efficiency reduced the estimated hazard of subsequent mortality by 32 percent. There was no association between sleep duration and survival.
“Sleep loss and other factors can influence the amount of melatonin secretion or block it altogether, and health problems associated with low melatonin, disrupted sleep, and/or disruption of the circadian rhythm are broad, including a potential risk factor for cancer,” said Sarah C. Markt, M.P.H., doctoral candidate in the Department of Epidemiology at Harvard School of Public Health in Boston. “We found that men who had higher levels of melatonin had a 75 percent reduced risk for developing advanced prostate cancer compared with men who had lower levels of melatonin.”