Some time back I posted sleep researcher Dr. Matt Kelly’s TED Talk on sleep, which I highly recommend. Now, the American Academy of Sleep Medicine (AASM) has issued a position paper which states unequivocally that “sleep is essential to health”.
As noted in the position paper, “Healthy sleep is important for cognitive functioning, mood, mental health, and cardiovascular, cerebrovascular, and metabolic health.” Anyone who has suffered through the daylight savings time change – that would be most of us – can tell you that even missing out on a single hour of sleep can leave you feeling off for a few days.
And many of us have likely had the experience of sacrificing sleep for school or work projects, adjusting to newborns, or other similar temporary situations, not to mention the occasional middle-of-the-night stress session.
But sleep disruption on a chronic scale has far-reaching repercussions, and has been “associated with an increased risk of mortality and contributes to both the individual risk and societal burden associated with several medical epidemics, including cardiovascular disease, diabetes, obesity, and cancer.”
In particular, shift work has been associated with an increased risk of cancer, due to the persistent disruption of the body’s biological clock, as reported in a recent CDC blog post based on reviews by the National Toxicology Program and the International Agency for Research on Cancer. Data came from both breast and prostate cancer surveys. [The CDC post does outline what shift workers can do to protect themselves.]
I suspect that data from shift workers will reveal the influence of factors other than simply how long one sleeps, for instance, the significant effect of melatonin’s known anticancer properties (Hill et al., 2015, Endocr Relat Cancer; Yi et al., 2017, Oncotarget; Bondy & Campbell, 2018, Int J Mol Sci).
According to the AASM position paper, the consensus among different sleep-related organizations is that adults require at least 7 hours of sleep regularly, with the range being 7-9 hours. While this seems straightforward, one meta-analysis (Lu et al., 2017, Biomed Res Int) of 10 studies suggested that sleeping excessive amounts (over 9 hours) was linked to an increased risk of estrogen-positive (but not estrogen-negative) breast cancer for women. At the same time, Xiao et al. (2016, Sleep Med) found that short sleep duration was associated with triple-negative (but not estrogen-positive) breast cancer in black women as compared to white women, suggesting racial disparities in the data, so further research is needed.
Confusing? Yes, this is clearly an area that calls for more study. Some clarification came recently from the publication of the “Million Woman Study”. This was an extensive prospective multi-year study of women in the UK that, you guessed it, found no association between breast cancer and sleep of any duration (Wong et al., 2021, Sleep). Nonetheless, the authors did note some shortcomings of the study, so this question is likely to be revisited.
Take home message? Conflicting studies aside, everyone would agree that good sleep hygiene (see CDC recommendations) is important no matter what your cancer risk. With our lives running 24/7 and sleep schedules constantly being disrupted, we should take a clue from the animals who settle down as the evening begins, like clockwork. We might have advanced as a civilization, but we can’t get past the reality that when it’s dark out, it’s time to hit the sack.