Have you slept enough this week? When did you last wake up without an alarm clock and not need caffeine? If either of these questions is “no,” you’re not alone. In many developed countries, more than a third of adults don’t get enough sleep.

You may be surprised by the consequences, though. Sleeping less than six hours a night weakens your immune system, increasing cancer risk. Insufficient rest appears to increase Alzheimer’s risk. Inadequate sleeping, even for a week, can cause pre-diabetes. Short sleeping increases the risk of blocked and brittle coronary arteries, leading to cardiovascular disease, stroke, and heart failure. Sleep disruption contributes to all major psychiatric conditions, including depression, anxiety, and suicidality.

If you’re tired, do you eat more? No accident. Too little sleep boosts a hormone that makes you hungry and lowers another that signals fullness. You want more food despite being full. Insufficient sleep causes adults and children to gain weight. If you diet without enough rest, you’ll lose lean body mass, not fat.

“I’ll sleep when I’m dead” is bad advice

The shorter your sleep, relative to the recommended seven to nine hours, the shorter your lifespan. “I’ll sleep when I’m dead” is bad advice. Adopting this mindset could shorten your life and reduce its quality. Sleep deprivation has a breaking point. Humans are the only species that will intentionally go without sleeping. The Center for Disease Control declared insufficient sleep a public health epidemic. Countries where sleeping-time has declined most dramatically over the past century, like the US, UK, Japan, South Korea, and several in western Europe, also have the highest rates of physical diseases and mental disorders.

Scientists lobby doctors to “prescribe” sleep. It’s painless and enjoyable medical advice. This is not a call for doctors to prescribe more sleeping pills, given the evidence of their harmful health effects.

Could lack of sleep kill you?

Two times yes. First, a rare genetic disorder starts with midlife insomnia. The patient stops sleeping after several months. They’ve lost many brain and body functions by this point. Few drugs help patients rest. The patient will die after 12-18 months without sleeping.

Second is driving while sleepy. Drowsy driving causes tens of thousands of accidents and deaths annually. Not only is the sleep-deprived person’s life at risk, but so are others. Fatigue-related errors cause one traffic death per hour in the U.S.

Science has historically failed to explain why we need sleep, contributing to society’s apathy. Sleeping was a biological mystery. Genetics, molecular biology, and high-powered digital technology have failed to unlock sleep’s vault. Nobel Prize–winner Francis Crick, who deduced DNA’s twisted-ladder structure, Roman educator Quintilian, and even Sigmund Freud all tried to decipher sleeping’s enigmatic code in vain.

Doctors and scientists couldn’t explain why we sleep until recently. We’ve known the functions of the three other basic drives—to eat, to drink, and to reproduce—for decades, if not centuries. The fourth biological drive, sleep, has eluded science for millennia.

Sleep is so health-relevant

Evolutionary explanations for sleep only deepen the mystery. It seems foolish from any angle. You can’t eat while sleeping. You cannot socialize. Can’t find a mate or reproduce. You can’t care for your children. Worse, sleeping leaves you vulnerable to predation. It is surely one of the most puzzling human behaviors.

Sleep evolved with—or soon after—life on Earth. It has persisted throughout evolution, so its benefits must outweigh its risks and detriments.

A different truth: sleeping is complex, interesting, and health-relevant. We sleep for a litany of functions that benefit our brains and bodies. There’s no major organ or brain process that isn’t improved by sleeping (and harmed when we don’t get enough). Nighttime health benefits shouldn’t be surprising. We’re awake for two-thirds of our lives and don’t accomplish just one thing. We do many things to ensure our survival and well-being. Why would we expect sleeping – and the 25-30 years it takes from our lives – to serve only one purpose?

In the past 20 years, we’ve learned that evolution didn’t make a huge mistake in creating sleep. Sleep’s health benefits can be refilled every 24 hours if desired.

Sleep’s health benefits can be refilled every 24 hours

Sleep helps the brain learn, memorize, and make logical decisions. Sleeping recalibrates our emotional brain circuits, helping us navigate social and psychological challenges the next day. Even the most impervious and controversial conscious experience, the dream, is being understood. Humans, like other species, benefit from dreaming. These gifts include a neurochemical bath that soothes painful memories and a virtual reality space that inspires creativity.

Sleep replenishes the immune system, preventing infection and illness. Sleeping regulates the body’s metabolism by balancing insulin and glucose. It also regulates appetite, helping us control weight through healthy eating rather than impulsiveness. Sleep maintains a healthy gut microbiome, where much of our nutritional health begins. Adequate sleeping lowers blood pressure and helps keep our hearts healthy.

Diet and exercise are crucial, yes. But sleep is now a major part of the health trinity. A bad night’s rest causes more physical and mental damage than a day without food or exercise. It’s hard to imagine a natural or medically manipulated state that improves physical and mental health more.

We no longer need to ask what sleep is good for based on new science. We now wonder if any biological functions don’t benefit from it.

Sleeping is the single most effective thing we can do to reset our brain and body health each day — Mother Nature’s best anti-death effort. Unfortunately, the people has not been clearly warned about the dangers of short nap. It’s the biggest omission in modern health conversations.

Source: “Why We Sleep – Unlocking the Power of Sleep and Dreams” – by Matthew Walker