There is a J-shaped association for total daily sleep duration with all-cause mortality and cardiovascular events, according to a study published online Dec. 5 in the European Heart Journal.

Chuangshi Wang, from McMaster University in Hamilton, Ontario, Canada, and colleagues examined the correlation of estimated total daily sleep duration and daytime nap duration with deaths and major cardiovascular events among 116,632 participants from seven regions.

The researchers identified 4,381 deaths and 4,365 major cardiovascular events after a median follow-up of 7.8 years. After adjustment for age and sex, both shorter (no more than six hours/day) and longer (more than eight hours/day) estimated total sleep durations correlated with an increased risk for the composite outcome. A J-shaped association was observed after adjustment for demographic characteristics, lifestyle behaviors, and health status. Those who slept no more than six hours per day had a nonsignificant trend for an increased risk for the composite outcome compared with sleeping six to eight hours per day. Researchers observed a significant trend for a greater risk for the composite outcome as estimated sleep duration increased. The risk for composite events was increased with daytime nap duration for those with more than six hours of nocturnal sleep duration, but not in those with six hours of sleep or less.

"Daytime naps are associated with excessive risks of major cardiovascular events and deaths except in those with less nocturnal sleep suggesting that this may be a compensatory mechanism when nocturnal sleep is short," the authors write.

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