Daniel E. Lieberman is a professor of human evolutionary biology at Harvard University and author of “Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding.”
Do you lose sleep over whether you sleep too little or too much? You can now relax, because scientists have figured out precisely how much sleep you really need. In a recent study in Nature, an international team of experts reports that the “sweet spot” for adults is between 6 hours 24 minutes and 7 hours 48 minutes. Less or more than this “Goldilocks” zone is associated with faster rates of aging in the brain, heart, liver and other vital organs, plus higher rates of illnesses such as heart disease and depression, and ultimately shorter lifespans.
You don’t need a medical degree to know that too little sleep is detrimental. Numerous studies have shown how sleep duration impacts health outcomes. Although there is plenty of variation from person to person, adults typically live longer and suffer from fewer major diseases if they sleep about seven hours most nights. The myth that eight hours is optimal has been debunked.
I’m being unfair to the new study, which is impressive. The researchers looked at data from hundreds of thousands of individuals who self-reported their sleep habits. In addition to examining the medical records of these participants, the researchers used sophisticated methods to analyze tissue samples from their organs to evaluate how they aged. They found that too little or too much sleep is associated with harming everything from the brain to the heart and gut. Damage to tissues throughout the body presumably underlies why insufficient or excess sleep causes people to age faster and die younger.
However, a major concern with the study is that it analyzed only associations and cannot distinguish between cause and effect. Since people who don’t feel well often sleep more, it’s possible that more than 7.8 hours of sleep was falsely identified as detrimental. Another drawback is that the study used notoriously inaccurate self-reported sleep data. (Do you know exactly how much sleep you got last night?) An additional flaw is that the researchers included mostly people of European ancestry. Even so, the study adds substantially to evidence of the health benefits of sleeping enough but not too much.
But how should the public use this evidence? Maybe learning how lack of sleep accelerates aging will serve as a wake-up call to those who shortchange themselves on sleep and induce them to go to bed earlier. Perhaps the relatively small percentage of people prone to oversleeping will set their alarm clocks to get up earlier. My worry, though, is with the roughly 35 percent of Americans who say they get less than seven hours of sleep, many of whom have insomnia.
Why? Because if someone suffers from insomnia, emphasizing that their lack of sleep might send them to an early grave could increase their anxiety and stress about sleep, thus exacerbating the problem. Anxiety and stress are major risk factors for insomnia because they stimulate the body to produce hormones such as cortisol that arouse us. Studies have shown that medicalizing sleeplessness sometimes worsens the problem by treating a common issue as a medical matter requiring diagnosis and treatment.
Meanwhile, the sleep industrial complex is ready to profit from the vicious cycle of sleep anxiety. You can buy special mattresses that keep your body at just the right temperature. There are ergonomic pillows, weighted blankets, bedroom curtains that block every photon of light and devices to make white noise. Also available are wearable technologies claiming to optimize sleep by measuring sleep quality and duration. And you can purchase prescription drugs or supplements.
Sadly, there is little evidence that most of these products are effective, and their reported benefits (some of which may be attributable to placebo effects) vary widely. For example, some people who use wearable sleep trackers find the devices to be helpful, but others become so preoccupied with their sleep data that they paradoxically develop trouble sleeping — a new condition dubbed “orthosomnia.”
Medical care is sometimes critical (a good example is treating sleep apnea), but it’s also useful to remember that how we sleep isn’t just biological but also cultural. Studies show that sleeping customs vary enormously from culture to culture and have changed over time. For most of human evolution, our ancestors slept outside in noisy groups and without pillows on hard surfaces with only straw, skins, bark or leaves for cover. They also sometimes woke up in the middle of the night. It’s only recently that we invented bedrooms and comforts such as mattresses.
I’m not suggesting you abandon your bed and pillow, but the next time you lie awake tossing and turning, don’t worry about whether you are getting the right amount of sleep. Instead, if you’re unsure about your sleep health, researchers suggest you ask yourself five simple questions:
Are you satisfied with your sleep?
Do you stay awake all day without dozing?
Are you asleep between 2 a.m. and 4 a.m.?
Do you spend less than 30 minutes awake at night?
Do you get between six and eight hours of sleep?
If your answers to these questions are not “usually” or “always,” then I hope you find relief through well-studied, effective approaches that reduce sleep-related anxiety and stress. These include developing good habits such as exercising, cognitive behavioral therapy and maintaining a regular sleep schedule.
The post How much sleep do you really need? It’s not 8 hours. appeared first on Washington Post.
