A Prospective Study on Habitual Duration of Sleep and Incidence of Breast Cancer in a Large Cohort of Women

Abstract

Mounting evidence suggests habitual sleep duration is associated with various health outcomes; both short and long sleep duration have been implicated in increased risk of cardiovascular disease, diabetes, and all-cause mortality. However, data on the relation between sleep duration and cancer risk are sparse and inconclusive. A link between low levels of melatonin, a hormone closely related to sleep, and increased risk of breast cancer has recently been suggested but it is unclear whether duration of sleep may affect breast cancer risk. We explored the association between habitual sleep duration reported in 1986 and subsequent risk of breast cancer in the Nurses' Health Study using Cox proportional hazards models. During 16 years of follow-up, 4,223 incident cases of breast cancer occurred among 77,418 women in this cohort. Compared with women sleeping 7 hours, covariateadjusted hazard ratios and 95% confidence intervals for those sleeping V5, 6, 8, and z9 hours were 0.93 (0.79-1.09), 0.98 (0.91-1.06), 1.05 (0.97-1.13), and 0.95 (0.82-1.11), respectively. A moderate trend in risk increase towards longer sleep duration was observed when analyses were restricted to participants who reported same sleep duration in 1986 and 2000 (P trend = 0.05). In this prospective study, we found no convincing evidence for an association between sleep duration and the incidence of breast cancer. (Cancer Res 2006; 66(10): 5521-5)

Sleep duration and the risk of prostate cancer: the Ohsaki Cohort Study

“…There have, however, been three observational studies of sleep duration and breast cancer risk (McElroy et al, 2006;Pinheiro et al, 2006). Among these, one reported a decreased risk in long sleepers (Verkasalo et al, 2005), the second reported no association (Pinheiro et al, 2006), whereas the third reported an increased risk in long sleepers (McElroy et al, 2006).…”

“…There have, however, been three observational studies of sleep duration and breast cancer risk (McElroy et al, 2006;Pinheiro et al, 2006). Among these, one reported a decreased risk in long sleepers (Verkasalo et al, 2005), the second reported no association (Pinheiro et al, 2006), whereas the third reported an increased risk in long sleepers (McElroy et al, 2006). Among possible reasons for these differences from our findings (apart from the site of cancer), McElroy et al (2006) conducted a casecontrol study while Pinheiro et al (2006) studied residential nurses in the United States with rotating shift work and varying timing of sleep so that generalising from their results may be inappropriate.…”

“…Sleep duration is associated with various health outcomes (Youngstedt and Kripke, 2004) including three observational studies of sleep duration and breast cancer (Verkasalo et al, 2005;McElroy et al, 2006;Pinheiro et al, 2006). Melatonin, which is secreted mainly from the pineal gland and plays a role in sleep duration, is suggested as one of the candidates responsible for the association in breast cancer (Brzezinski, 1997;Schernhammer and Schulmeister, 2004) as it influences the synthesis and secretion of sex hormones by promoting the release of gonadotropin-releasing hormone (Martin and Klein, 1976;Aleandri et al, 1996).…”

Sleep duration and the risk of breast cancer: the Ohsaki Cohort Study

“…In relation to melatonin secretion, there have been several observational studies on night work or visual impairment and breast cancer (Feychting et al, 1998;Verkasalo et al, 1999;Kliukiene et al, 2001;Schernhammer et al, 2001;Megdal et al, 2005;Pukkala et al, 2006;Schwartzbaum et al, 2007). In addition, there have been three prospective cohort studies of sleep duration and the risk of breast cancer, although with inconsistent findings (Verkasalo et al, 2005;Pinheiro et al, 2006;Wu et al, 2008).…”

Sleep duration and cancer risk: time to use a “sleep-years” index?

“…Dr. Sturgeon et al [4] now provide the sixth study on the issues concerned and report mixed results. Overall, with regard to how long one sleeps, first [4][5][6][7][8]-but not all [9]-epidemiological evidence could be viewed in line with increased cancer risks in those who sleep less than others [2].…”