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

Abstract

With a focus on melatonin, a recent paper in the Journal investigated the hypothesis that endometrial cancer might be associated with the duration, and ultimately, amount of sleep. The authors found that ''[s]elfreported sleep duration may not adequately represent melatonin levels.'' The authors also concluded that there was ''weak evidence of an association between sleep duration and endometrial cancer risk.'' Overall, these are interesting observations because primarily experimental and mechanistic research from many angles supports the study's notion that inappropriate sleep may be a determinant of cancer risk. To find out whether this is so in man, rather than assigning study individuals to fixed or average ''baseline sleep categories'' i.e., B5, 6, 7, 8, C9 h of habitual sleep in the present study, the accumulated amount of sleep over decades should be reconstructed in retrospective or constructed in prospective studies. To achieve this end, future epidemiological studies may want to use a sleep-years index [SYI]. This simple exposure parameter promises to be a sensible, feasible, and affordable way to approximate cumulative time spent at sleep in critical time windows over many years which we should expect to be relevant for the development of cancer. The SYI could be tested and used in observational studies which promise to be comparable and can be merged. This commentary provides roots of the index and explains why and how it should be used and how it could be interpreted in rigorous studies of biologically plausible links between sleep, on the one hand, and the development of internal cancers, on the other. This commentary also points out limitations of interpreting the SYI. It is emphasized that, where possible, the SYI should be assessed independently of (a) other sleep facets-such as quality-and of (b) known or suspected cancer risk factors. The respective contribution of (a) and (b) to risk must then be assessed during the analyses. Overall, the suggested inclusion and standardization of assessing sleep duration could be an important step forward when evaluating possible cancer risks in relation to sleep. Finally, the proposed approach may prove useful beyond sleep epidemiology per se: to exemplify, research into suggested causal links between disrupted natural sleepwakefulness cycles and increased cancer risks in shiftworkers could also benefit.

Sleep duration and breast cancer risk among black and white women

“…Second, we only had a single report of sleep duration, and were not able to capture a long term sleep patterns among the study population. As argued by a recent paper, to better understand the relationship between sleep and cancer risk, it may be important to evaluate the cumulative exposure of short or long sleep in critical time windows of cancer development (25). Third, we lacked information on other important aspects of sleep and circadian rhythm which may also influence breast cancer risk, such as sleep quality, snoring, sleep disorder, and chronotype (2).…”

Sleep duration and breast cancer risk: A meta‐analysis of observational studies

“…Accordingly, a hypothesis linking sleep duration and cancer risk has been proposed. However, several studies have suggested that there is no relationship between self‐reported sleep duration and melatonin levels . This may possibly explain why there is no association between sleep duration and breast cancer risk.…”

Sleep, mortality and beyond: A magician can't pull more from the hat than has been put in earlier

“…In effect, rather than limiting study individuals to the prevailing "one-category-ofsleep-duration-fits-decades"-approach, longitudinal information could allow to test accumulated amounts of sleep [5] as an alternative exposure measure in sleep epidemiology. • Sleep quality also should be taken into consideration as a potential confounding residual.…”