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Medical Myths Medical Myths

Sleep -- Can You Get Too Much of a Good Thing?

September 25, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

It's important to get a good night's sleep.

I have to agree with this one. And by "a good night's sleep" we usually mean that it's best to get plenty of sleep and avoid sleep deprivation.

Is it possible that it's just as important to avoid getting too much sleep? Before trying to answer this question, it's useful to think about the purpose of sleep.

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Why Do We Need Sleep?

Sleep researchers have discovered a lot about sleep. We know there are several different stages of sleep, each of which seems important in different ways.

  • Rapid-eye-movement (REM) sleep appears to be vital for the formation of long-term memory.
  • Non-REM sleep plays a role in promoting concentration and restoring energy.

Sleep also seems to be important for normal immune function and eating patterns. Some sleep experts believe that sleep deprivation may be contributing to the current epidemic of obesity.

These insights have come mainly from studying what happens when sleep is disrupted or limited. But, they don't answer a key question: Why do humans (and the rest of the animal kingdom) have a need to sleep?

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How Much Sleep Is "Normal?"

Newborns can sleep up to 18 hours a day. But that would clearly be abnormal for an adult!

The amount of sleep a person needs varies by age. An infant may sleep most of the day; a toddler may need 12 hours; and a school-age child might require 10 or 11 hours. A teenager typically requires up to 9 hours a night (though it seems most don't get nearly that much). The average adult needs 7 to 9 hours.

But there are problems with all of these estimates:

  • There's no single way to define the ideal amount of sleep.
  • People who are otherwise "normal," healthy and similar to one another vary significantly in how much sleep they need.
  • A person may need different amounts of sleep at different times in his or her life. Besides age, your stress level, illness and activity level (and other factors) can affect how much sleep you need at any given time.
  • There is disagreement about how much sleep older adults need. For example, some experts say they need less sleep than younger adults. Others say older adults need just as much sleep as younger adults but have more trouble getting it (so that less sleep becomes "normal" for them).

The amount of sleep you need can be defined in at least two ways. It can be:

  1. The amount you'd sleep if you went to bed and got up whenever you felt like it, without the use of an alarm clock and without respect to sunset or sunrise.
  2. The amount you need to feel rested and alert in the morning, able to perform at your best and without daytime sleepiness.

These two definitions could provide different amounts for the same person.

If you asked everyone you know how much sleep they want (or need), it's likely you'd get significantly different answers — and some might say that they have no idea!

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What's Too Much, Too Little and Just Right?

It seems to me that sleep is a bit like the porridge in the story of Goldilocks and The Three Bears. We're all looking for the amount that's "just right" but many of us never find it.

Getting too little sleep is remarkably common. About 25% of Americans have occasional insomnia; 10% or more (30 to 40 million people!) have chronic insomnia. It's estimated that half of people over age 60 have significant problems getting enough sleep. Although reliable numbers are not easy to find, one large study found that approximately 10% of the American population reported sleeping at least 9 hours per night.

So, if these estimates are accurate, a relatively small number of people are happy with the amount of sleep they get each night.

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Does Amount Matter?

You might wonder if it really matters whether you get more or less than the ideal amount of sleep. It's tough to answer because, again, it's hard to define an ideal amount of sleep. Also, the effects of sleep are difficult to separate from other variables that can affect sleep quality or duration.

However, studies have linked short sleep duration — 5 hours or less each night — with a number of health problems, including hypertension and diabetes. Sleep deprivation is also a major contributor to car accidents, accounting for an estimated 100,000 accidents and 1,500 deaths per year in this country.

It turns out there may also be health problems associated with too much sleep.

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The Health Effects of "Too Much" Sleep

Large, well-designed studies have analyzed the relationship between the amount of sleep and length of life. Thousands of people have answered detailed questionnaires about their sleep habits and their health status over many years.

I was surprised to learn that the death rates for people who sleep the least and the most are higher than those people whose sleep time falls in the middle.

The reason isn't clear. My assumption was that another variable — say, overall health, access to medical care or recreational drug use — might explain the relationship. For example, people living in poverty might sleep poorly due to the stress of their everyday lives. Also, their health might suffer as a result of that stress and limited access to medical care. People who sleep excessively might be drinking too much, which could impair their health.

Studies trying to account for such "confounders" — factors other than sleep itself that might help us understand the relationship between excessive sleep and reduced longevity — have failed to adequately explain it. However, several conditions appear to be associated with longer sleep duration, including:

  • Heart disease
  • Diabetes
  • Obesity
  • Depression
  • Low social and economic levels

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Can Sleeping Too Much Be a Sign of Illness?

Even though plenty of healthy people sleep 9 hours or more, excessive sleep can be due to a number of common health problems, including:

  • Thyroid disease
  • Kidney or liver disease
  • A sleep disorder such as obstructive sleep apnea
  • Dementia
  • Depression

Medications can also cause sleepiness and contribute to sleeping longer.

If you've noticed that you need more sleep than in the past, it may be a good idea to see your doctor for evaluation.

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Can Changing How Much You Sleep Improve Your Health?

Given what we know about the relationship between sleep duration and longevity, you might wonder whether changing how many hours you sleep might impact your health or how long you live.

Because short (or long) sleep duration may not actually cause the shorter lifespan, changing sleep habits might not have a direct effect on how long you live. In addition, any given individual who sleeps more or less than average could have much more important health issues affecting longevity.

As a result, getting more sleep (if you now get less than 5 or 6 hours of sleep per night) or less sleep (if you sleep for 9 or more hours per night) won't necessarily help you live longer. We simply don't have the evidence to prove that changing how much you sleep will directly change your risk of dying early.

And let's face it: Each person has different sleep challenges. There's work, school, family events, travel and changes in the amount of daylight. For some, there's a baby that needs to be fed or a pet that needs to be walked. The idea that we can simply decide to get the right amount of sleep (like a New Year's resolution) may be unrealistic.

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The Bottom Line

It's hard to get "just enough" sleep. In fact, it's also hard to define what just enough is. It's also hard to control with precision how much we sleep given all of the things in our lives that affect how well and how long we sleep.

Still, as elusive as the right amount of sleep may be, the idea that there's no such thing as "too much sleep" may be a myth. We can all agree it's important to get a good night's sleep. But that may mean more than just getting enough. It might also mean not getting too much.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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