Long Sleep: Is There Such Thing as Too Much of a Good Thing?

There exists a U-shaped relationship between sleep length and mortality, with short (<7h) and long (>9h) sleep both associated with poor health. However, given that the propensity for sleep and the circadian drive for wakefulness bookend a sleep period even when further opportunity presents itself, it remains unclear whether long sleepers are indeed sleeping longer than an average sleep duration, or simply spending longer in bed. Given that self-reported long sleepers are more likely to have poor physical or mental health, preexisting health conditions may predispose these individuals to excess time in bed that is not necessarily a longer-than-average sleep duration. Depression, chronic pain, and frailty could all be likely contributors. There may be a genetic basis for long sleep, or impairments in the neural circuitry in some individuals, as well as sex differences. However, while long sleep is generally associated with elevated cardiovascular disease risk and worse mental health, some studies—particularly among older adults and cancer survivors—have suggested benefits to a longer sleep duration. More studies that incorporate objective as well as self-reported measures of sleep duration are needed.