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)?


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.


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).


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.


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.

Clinical Topics: Prevention, Sleep Apnea

Keywords: Body Mass Index, Cardiovascular Diseases, Health Status, Life Style, Outcome Assessment (Health Care), Primary Prevention, Risk, Sleep, Sleep Deprivation

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