Why do we sleep

A good sleep tracker can reveal the quantity and quality of your sleep, but there’s one thing it can’t tell you: why do we need to sleep in the first place? Surprisingly, nobody knows the answer to this question.

Sleep remains one of nature’s most mysterious and hotly debated activities. Of course, we know that we feel terrible if we go to bed too late, or wake up too often or too early. But the purpose of sleep has remained elusive. There are lots of questions, few definitive answers and numerous theories.

Evolutionary scientists hypothesized that sleep was nature’s way of forcing our prehistoric ancestors to seek shelter at night when they would be most vulnerable to predators. But as we began to learn more about the brain and, specifically, the distinctly different stages of sleep, scientists came to realize that there must be some greater purpose to an activity that consumes about one-third of our lives.

You may have heard about the role of sleep in learning and memory, the “memory consolidation” theory. This school of thought suggests that the primary role of sleep is to help our brains process new information we acquire during the day, to prime our brains to absorb yet more information the next day. In recent decades, however, thousands of studies have revealed the importance of sleep for all aspects of health and wellbeing, well beyond learning and memory. For example, there is a strong link between lack of sleep and heart disease, as well as Type 2 diabetes, obesity and high blood pressure. Chronic sleep deprivation is also associated with a greater risk for breast, colon and other cancers. Yet, despite it’s obvious importance, we still don’t know precisely why we do it, nor do we know exactly how much sleep we actually need.

How Much Sleep Do You Need?

This is a no brainer, right? For years we’ve been told that eight hours a night is the perfect amount of sleep. As it turns out, it may not be quite that simple. Instead of blanket recommendations, many sleep specialists now talk about “basal sleep need,” that is, the precise amount of sleep someone needs every night to function well.  Basal sleep need may vary somewhat from person to person depending on genetics, age and other factors. That’s why some people do well with seven hours sleep, while other may need close to nine.  What happens if you don’t meet your nightly basal sleep need? You start to accumulate a  “sleep debt.” Getting adequate rest on subsequent nights can make up a night or two of “sleep debt,” but chronic sleep debt is a real problem.

What we do know is that most studies suggest that seven to eight hours of sleep a night appears optimal for most people, although some require up to nine hours per night. Sleeping more than nine hours a night is linked to poor health, but that may have little to do with sleep and more to do with an underlying condition that is creating excess fatigue.  We also know that most people don’t get enough sleep. On average, the typical American adult gets 6.7 hours of sleep a night, and many sleep a lot less.

How can you assess your own sleep needs? The first and most obvious way is to think about how you feel. Do you wake up feeling refreshed? Do you always want to sleep a bit longer? Can you get through the day without feeling exhausted, or having to pump yourself up with caffeine? Do you find yourself dosing off throughout the day? These are the classic signs that you may be in sleep debt.

An at home sleep study can also help you figure out whether you are meeting your sleep needs.

What if You’re Shortchanged on Sleep?

The dangers of consistently getting too little sleep have been well documented, but until recently, we didn’t understand the underlying mechanism that triggered these problems. A recent study, however, showed the devastating impact that chronic sleep deprivation can have on our genes. A 2013 study published in the Proceedings of the National Academy found that people who slept less than six hours a night experienced changes in the activity of more than 700 genes that control a wide range of systems in the body, including immune function, metabolism and the way the body handles stress. Sleeping too little can also disrupt your sleep/wake cycles, which has been implicated in shorter lifespan.  

People who sleep six hours a night or less are more likely to be overweight or obese than those who get eight hours sleep. They’re also more prone to metabolic disorders like insulin resistance, which can lead to Type 2 diabetes and are more susceptible to different types of cancer.

Here’s the really scary statistic: People who sleep only five hours or less a night are 15% more likely to die prematurely.

Of course, the quality of your sleep is as important as the quantity of your sleep. For example, according to a 2011 in Hypertension, men who don’t get enough deep “slow wave sleep” have an 80% chance of developing high blood pressure. Earlier studies have shown a connection between a deficiency in deep sleep and elevated blood sugar levels which could lead to diabetes. An at home sleep study can help you assess whether or not you’re getting enough of the “deep” sleep you need to stay well.