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Association of Sleep Time and Naps With Mortality and CV Events
Study Questions:
What is the association of estimated total daily sleep duration and daytime nap duration with deaths and major cardiovascular events (CVEs)?
Methods:
The authors estimated the durations of total daily sleep and daytime naps based on the amount of time in bed and self-reported napping time, and examined the associations between them and the composite outcome of deaths and major CVEs in 116,632 participants from seven regions. Age range was 35-70 years. Information was obtained by questionnaires. Exclusions included events in the first 2 years, shift workers, those less healthy with known disability, symptoms, or those with prior non-CV and noncancer diseases. Sensitivity analysis was performed by adjustment of those with a body mass index (BMI) ≥30 kg/m2.
Results:
Mean age was 51 years, mean BMI was 26 kg/m2, and about 40% were male. After a median follow-up of 7.8 years, there were 4,381 deaths and 4,365 major CVEs. Both shorter (≤6 hours/day) and longer (>8 hours/day) estimated total sleep durations were associated with an increased risk of the composite outcome when adjusted for age and sex. After adjustment for demographic characteristics, lifestyle behaviors, and health status, a J-shaped association was observed. Compared with sleeping 6–8 hours/day, those who slept ≤6 hours/day had a nonsignificant trend for increased risk of the composite outcome (hazard ratio [HR], 1.09). As estimated sleep duration increased, there was a significant trend for a greater risk of the composite outcome HR of 1.05, 1.17, and 1.41 for 8–9 hours/day, 9–10 hours/day, and >10 hours/day, ptrend < 0.0001, respectively. The results were similar for each of all-cause mortality and major CVEs. Daytime nap duration was associated with an increased risk of the composite events in those with over 6 hours of nocturnal sleep duration, but not in shorter nocturnal sleepers (≤6 hours).
Conclusions:
Estimated total sleep duration of 6–8 hours/day is associated with the lowest risk of deaths and major CVEs. Daytime napping is associated with increased risks of major CV events and deaths in those with >6 hours of nighttime sleep, but not in those sleeping ≤6 hours/night.
Perspective:
Recent US recommendations for optimal duration of sleep for adults is ≥7 hours per night. Daytime napping is often thought of as a regional (warm climate), cultural, or ethnic trait. That it was associated with increase in CVEs and all-cause mortality in persons who sleep >6 hours per night is surprising. While the strength of the study is the number of participants and diverse countries of origin, the data regarding amount of sleep each night; underlying medical diagnosis; the fatigue associated with work, stress, and heat; and nutrition could not be assessed. The precise value of a nap remains unclear to me, but always seems generally helpful.
Keywords: Body Mass Index, Cardiovascular Diseases, Health Status, Life Style, Outcome Assessment, Health Care, Primary Prevention, Risk, Sleep, Sleep Deprivation
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