24 April, 2017:
A friend has just told me that sleep is a waste of time, because every minute being awake does count and should be used to enjoy life. Well, I guess he was wrong, since sleep is mandatory not only for relaxation, but also for the initiation of many active neuro-physiological processes which are vital. Extreme and prolonged deprivation of sleep may even eventually lead to death. The duration of sleep seems an important factor in maintaining optimal health. There is a consensus that a 7-hour night sleep should be recommended , whereas shorter or longer sleeps might be associated with a higher rate of health derangements and mortality risk . Although there is probably no gender difference in the impact of sleep duration, herein are some clinical data related to women and menopause.
Cardiovascular disease: In the Women's Health Initiative observational study (n = 86,329; 50–79 years old, 10.3 years follow-up), shorter (5 h or less) and longer (10 h or more) sleep duration demonstrated significantly higher incident coronary heart disease (CHD) (25%) and cardiovascular disease (19%) in age- and race-adjusted models, but this was not significant in fully adjusted models . Women with long sleep demonstrated the greatest risk of incident CHD compared to midrange sleep duration (hazard ratio =1.93, 95% CI 1.06–3.51) in fully adjusted models.
Hypertension: The Nurses' Health Study investigated the relationships between sleep duration and hypertension among women whose sleep durations were self-reported (n = 84,674) [4)]. The prevalence of hypertension was significantly higher among women who slept 5 h or less per night (odds ratio = 1.19, 95% CI 1.14–1.25) compared with 7 h, but further analysis showed that this association was only seen in those aged < 50 years.
Diabetes mellitus: A recent study used data from the China Kadoorie Biobank, coming from a rural county . Sleep duration was shown to have a U-shaped association with diabetes in 33,677 women, in particular in postmenopausal women after adjustment for potential confounders. Compared with 7-h sleepers, odds ratios of sleep duration 5 h or less and 10 h or more for diabetes were 1.32 (95% CI 1.02–1.69) and 1.30 (95% CI 1.03–1.65), respectively.
Cancer: The WHI observational study showed that deviation from the ideal 7-h night sleep increases the risk for colorectal cancer . There were 851 incident cases with an average 11.3 years of follow-up. Compared with 7 h of sleep, the hazard ratios were 1.36 (95% CI 1.06–1.74) and 1.47 (95% CI 1.10–1.96) for short (5 h or less) and long (9 h or more) sleep duration. The Nurses' Health Study experience was summarized as 'no convincing evidence for an association between sleep duration and the incidence of breast cancer' . In few other studies, results were mixed, either a small reduced risk or a small increased risk for women who deviated from the optimal sleep duration.
Cognition: Both the Nurses' Health and WHI studies demonstrated an adverse impact of shorter or longer sleep durations on cognitive function . Also, women whose sleep duration changed by 2 h or more per day over time had worse cognition than women with no change in sleep duration.
To note, despite statistically significant associations between sleep duration and many health aspects, the excessive risks are relatively small or modest, when converted into absolute numbers. Still, sleep is needed for maintaining our normal physiology, and keeping the recommended schedule of a 7-h sleep duration per night will probably promote better health.
Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel
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