1. Sleep duration, when adjusted for body mass index (BMI), had an association with all-cause mortality at lower and higher durations.
2. Short and long sleep duration was associated with increased cardiovascular mortality risk and other-case mortality in men. Long sleep duration was also associated with an increased cancer mortality risk and other-case mortality in women.
Evidence Rating Level: 2 (Good)
Study Rundown: Long and short sleep duration is a known risk factor associated with all-cause mortality. However, studies differ in their definition of long and short sleep and their follow-up time and subgroup analysis. This study analyzed the all-cause mortality risk of long and short sleep in healthy East Asians, with additional subgroup analysis stratified by sex, age, and body mass index (BMI). 322,721 participants with complete age, sex, and sleep duration information from 9 different cohorts were grouped as getting <6 hours, 6 hours, 7 hours, 8 hours, 9 hours, and 10+ hours of sleep for this metanalysis. The studies followed participants for an average of 13.7 years. 13.7% of the men in this analysis died at some point during their follow-up compared to 7.7% of women. Sleep duration was associated with all-cause mortality, with increased risk at lower and higher durations (J-shaped distribution). 10+ hour sleep was associated with an increased risk of mortality for men and women. Increased cardiovascular mortality risk was associated with <6 hours or >9 hours in men and <6-hour or >6-hour duration in women. Increased cancer mortality risk was associated with >7-hour sleep duration in men >10-hour sleep duration in women. Other-cause mortality was also affected by sex, as men had increased risk at <6-hour or >6-hour duration, while women only had increased risk when getting >7 hours of sleep. This study is the largest analysis of sleep duration that subgroups by sex. Another advantage is the important adjustment for BMI. While the results may be generalizable throughout an East Asian population, the studies exclusively draw from this pool and may not be further generalizable. The heterogeneous inclusion in the amalgamated studies of naps as counting towards total sleep may underestimate sleep duration and thus the association with mortality. A further limitation is that sleep duration was assessed at only one timepoint and may be highly variable in some participants. This metanalysis cannot infer causality given it pools observational studies.
Relevant Reading: Sleep duration and mortality – Does weekend sleep matter?
In-Depth [systematic review and meta-analysis]: 9 cohorts from Japan, China, Singapore, and Korea with available sleep data (n = 450,532) with data from January 1, 1984, to December 31, 2002, were pooled. This study excluded those missing sex, age, or follow-up time data or those who died in the first 5 years of follow-up to avoid reverse causality. Thus only healthy adults with information on confounding variables were included (n = 322,721). The average follow-up was 14.0±5.0 years for men and 13.4±5.3 years for women (n = 322,721, age = 54.5±9.2 years; 55.3% female). Most men slept 8 hours (n = 50,570) while the most common sleep duration of women was 7 hours (n = 60,319). 19,419 male deaths occurred (n = 144,179) and 13,768 female deaths occurred (n = 178,542) during the study. For both men and women ( = 8.64, P = 0.12), sleep duration had a J-shaped association with all-cause mortality. There was a strong association detected between long sleep duration (10+ hours) and mortality for both men (HR = 1.43, 95%CI = 1.34-1.53) and women (HR = 1.55, 95%CI = 1.42-1.70). Sex modified the cardiovascular mortality risk ( = 13.47, P = 0.02). Men had an association between high cardiovascular mortality and sleep duration of <6 hours or >9 hours. Women had an increased cardiovascular mortality risk at all sleep duration except 6 hours. Sex also modified the association of sleep duration and cancer mortality risk ( = 16.04, P = 0.007). Men that slept >7 hours had increased cancer mortality, while only women that slept >10 hours experienced this increased mortality risk. Finally, sex also modified other-cause mortality ( = 12.79, P = 0.03). For men, other-cause mortality risk was increased in all sleep categories except 6 hours of sleep, while for women it was only increased in groups getting >7 hours of sleep.
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