Too little sleep, and too much, affect memory

Howard LeWine, M.D.

Chief Medical Editor, Harvard Health Publishing

When it comes to memory, sleep is a Goldilocks issue: both too much and too little aren’t good. Aim for “just right,” says a report from the Harvard-based Nurses’ Health Study.

“Our findings suggest that getting an ‘average’ amount of sleep, seven hours per day, may help maintain memory in later life and that clinical interventions based on sleep therapy should be examined for the prevention of [mental] impairment,” said study leader Elizabeth Devore, an instructor in medicine at Harvard-affiliated Brigham and Women’s Hospital in Boston.

A group of women taking part in the Nurses’ Health Study were asked about their sleep habits in 1986 and 2000, and were interviewed about memory and thinking skills three times over a later six-year period. Devore and her colleagues observed worse performance on brain testing among women who slept five hours or fewer per night or nine hours or more, compared with those getting seven to eight hours of sleep a night. Their findings were published online in the Journal of the American Geriatrics Society.

The researchers estimated that under-sleepers and over-sleepers were mentally two years older than the women who got seven to eight hours of shut-eye a night.

Beyond memory

Although this study couldn’t prove that getting too little or too much sleep causes memory and thinking problems, it’s in line with other work showing the potentially harmful effects of poor sleep. Previous research has linked poor sleep with higher risks of heart disease and stroke, type 2 diabetes, and depression.

How might sleep affect memory? People who are persistently sleep deprived are more likely to have high blood pressure, diabetes, and narrowed blood vessels. Each of these can decrease blood flow inside the brain. Brain cells need a lot of oxygen and sugar, so blood flow problems could affect their ability to work properly.

Poor sleep could affect the brain in another way. Sleep-deprived mice develop more deposits of a protein called beta amyloid in the brain compared with mice allowed to sleep normally. In humans, beta amyloid deposits in the brain are linked to declines in memory and thinking and also increase the risk of dementia.

What about people who sleep too much? People who spend more than nine or 10 hours a night in bed often have poor sleep quality. So for both too little and too much sleep, the important number may be the hours of quality sleep.

Another possibility is a two-way street between sleep and memory: sleep quality may affect memory and thinking, and the brain changes that cause memory and thinking problems may disturb sleep.

Getting better sleep

Here are 12 tips for getting better sleep:

  • Establish a regular bedtime and a relaxing bedtime routine—examples might include taking a warm bath or listening to soothing music.
  • Use your bed only for sleeping or lovemaking. Avoid reading and watching television in bed.
  • If you can’t fall asleep after 15 to 20 minutes, get out of bed and go into another room. Do something relaxing, such as reading quietly with a dim light. Don’t watch television or use a computer, since the light from their screens has an arousing effect. When you feel sleepy, get back into bed. Don’t delay your scheduled wake-up time to make up for lost sleep.
  • Get plenty of exercise. Build up to 45 minutes of moderate exercise nearly every day. Get your exercise early in the day. Try some easy stretching exercises or yoga to relax your muscles and your mind at bedtime.
  • Whenever possible, schedule stressful or demanding tasks early in the day and less challenging activities later. This helps you wind down at the end of your day.
  • Don’t go to bed hungry, but don’t eat a big meal right before getting into bed. If you want a bedtime snack, keep it bland and light.
  • Limit caffeine and consume none after 2 p.m.
  • To decrease middle-of-the-night urination, limit fluid intake after dinner.
  • Avoid alcohol after dinnertime. Although many people think of it as a sedative, it can get in the way of quality sleep.
  • Be sure your bed is comfortable and your bedroom is dark and quiet. Consider a sleep mask or earplugs.
  • Don’t take long naps during the day. If you need a nap, restrict it to 20 to 30 minutes in the early afternoon.
  • Practice relaxation breathing. Use slow breaths, especially when you exhale.



    I just wanna say thank you for your article because this article was very useful and helped me to learn.

  2. Jen

    Through out day our mind is continuously working even then we are not working it is the only m/c which human can not build it works continuously hence in 24 hours it needs min 6 hours of rest if it don’t get that much amount of rest then obviously it’s functions stop working slowly slowly.

  3. Maureen Green

    Another great post. Thank you, thank you.


    All true. I sleep 5 hours and sometimes forget such simple names, numbers. Thank you for this article

  5. mukund lal

    hi above is very good article,define what is cicaridian sleep.if you are not taking a sound sleep in last night it can affect your next morning.


    I got useful information about sleep. Sleep plays important role during the whole day. If you take too little sleep. You will get tired next day. it is right thing that too much sleep affects the memory.


    This is a good article. I know I sometimes don’t sleep well and I’m tired the next day. I think it’s worse when I sleep too much.

  8. Almaira

    Useful information, articles like these that I find useful is clear and concise, thank you for all the contributions and lifestyles have become the trend of today and the future

  9. Scott

    “Use your bed only for sleeping or lovemaking. Avoid reading and watching television in bed.” is a good one. Watching TV in bed can effect REM sleep. Also caffeine even after 12 pm can affect sleep in my experience.


    Great article! Not only is getting enough sleep absolutely imperative to good health and well being, the quality of your bedding makes ALL the difference! If you’re going to spend a third of your life in bed, make it a good bed! I didn’t figure this one one until I was 32 years old.
    Practice your breathing as well… get some help if necessary.

    Keep up the good work

  11. Mo

    you should consider doing research on polyphasic sleeping.
    It has been attempted and studied by a few people but not a single proper experiment has been attempted.

    I’m personally sleeping 4 hours a day currently without any significant decrease in my awareness. [ went down as low as 2 h a day without heavy physical exercise].. but would it work for everyone that properly adapts ?


    Those 12 tips for better sleep worked great for me.


    Exercise definitely helps, I’ve never known anyone who does physical labor all day have a problem falling asleep. That said, if you can exercise 45 minutes a day in a safe manner, using enough intensity – it’s a huge step in the right direction. Also, making sure not too eat too much as indigestion, bloating etc can affect sleep. Great post, thanks! –

  14. nicola

    Many bad and good effects are available for sleep.Good sleep also helps to get better skin on our body.

  15. Jed

    Hi, nice article


    Hi there,
    Again a great informative article from the Harvard health Blog..Regular proper sleep is more important for the good health..i sleeps 5 hrs a day but sometime i also sleeps in day. According to a study conducted “during sleep the brain repairs itself to better acquire new information” so regular limited sleep is very much important!



    i never knew about these kind of severe bad effects of less sleeping and over sleeping, i mean what you have described and explained above like heart diseases, stroke, type ii diabetes, depression etc. i feel very lucky to have read your article. thanks for sharing, Mr.Howard 🙂

  18. Evy

    that’s a very good article and tips..too little or too much in anything (not just in sleep) is not good..

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