MD Stein - Sleep Trouble: Too Little or Too Much
Is there an optimal number of hours that we should sleep every night? Or put another way, is conventional wisdom that adults should sleep 8 hours actually good advice? In fact, it’s not: across the population, those who report 7 hours of sleep live longer than those who regularly sleep 8 hours or more.
The reasons for longer sleep reducing survival are hard to explain. Long sleep duration may simply be a marker of poor health. The effect of oversleeping on mortality may be indirect, and more often the result of associated conditions—depression, inactivity, unemployment—which have been associated with both prolonged sleep and reduced survival. Still, too much sleep has been correlated with cardiovascular disease, high blood pressure, and overall mortality rates, particularly among those older than 60. Should long sleepers try to restrict their sleep to increase longevity? There’s no data to provide an answer. Would anyone be willing to participate in this experiment?
At the other end of the spectrum, sleep deprivation—usually defined as less than 5 hours of sleep per night on average—is far more common than 8 hours of sleep, and appears to be even worse for your health. Over the past generation, societal changes have led to longer work hours, more shift-work, and round-the-clock availability of commodities, and greater time spent pursuing leisure activities, reducing the hours of sleep. A greater proportion of Americans today report greater fatigue and daytime sleepiness than they did a generation ago.
Lack of sleep produces dramatic changes in metabolic, endocrine and immune function. Currently explained at the cellular level by lower production of leptin and higher amounts of ghrelin, lack of sleep increases appetite and caloric intake, reduces energy use, and facilitates weight gain. Blood sugar problems and cardiovascular risks ensue. Sleep deprivation also triggers a low-grade, whole-body inflammation, like having a chronic viral infection. Although there are people with “short sleep” genes who are biologically inclined to sleep very few hours with no ill effects, for most people consistently sleeping 5 hours or less puts you in a high risk group. So the optimal number of hours to sleep seems to be between 5 and 8.
Lots of factors contribute to chronic sleep loss, for instance, pain, lung disease, and urinary problems. Others factors, such as caffeine and alcohol use, and cigarette smoking are also modifiable. Sleep is also determined by our working and living environments. Millions of Americans use sleeping pills, which offer no promise for the long-term correction of short sleep, a subject I will take up in a future column. However, increases in sleep from less than 5 hours to 7 hours on a regular basis has been associated with decreased risk of mortality in some people, a reason for cautious optimism.
Total hours only imperfectly captures whether your sleep is deep, restful, or interrupted, or the number of hours you spend in bed. But most people accurately report the number of hours they usually sleep, and it’s the one with health implications. Sleeping too little or too much are both dangerous. There is an increased risk of dying at either end of the spectrum.