Most sleep advice is about getting more. But there is a second worry, quieter and just as common: what if I sleep too much? A ten-hour weekend, a run of long nights during a hard month, a partner who can sleep until noon. Is there a point where more sleep stops being good for you?

There is a point where experts stop recommending more, and a body of research that links long sleep with poorer health. What that research can and cannot show is the interesting part. None of this is medical advice.

Where the recommendations stop

Two expert panels published adult sleep recommendations in 2015.

The American Academy of Sleep Medicine (AASM) and the Sleep Research Society said adults should sleep 7 or more hours a night on a regular basis. On the upper end their statement is careful: sleeping more than 9 hours a night on a regular basis "may be appropriate for young adults, individuals recovering from sleep debt, and individuals with illnesses". For everyone else, "it is uncertain whether sleeping more than 9 hours per night is associated with health risk."

The National Sleep Foundation's panel recommended 7–9 hours for young adults and adults, and 7–8 hours from 65. It added that durations outside the recommended range may be appropriate for some people, but that "deviating far from the normal range is rare", and that people who habitually sleep well outside it may be showing signs of a health problem, or, if they do it by choice, may be compromising their health.

So in plain terms: for a healthy adult, regularly sleeping more than about 9 hours is where the experts stop saying "more is fine". It is not a line past which harm is proven. It is the edge of what they are confident recommending.

What the big studies found

The worry about long sleep comes mostly from large population studies that ask people how long they sleep and then follow them for years.

A 2010 meta-analysis by Francesco Cappuccio and colleagues pooled 16 prospective studies, with 27 cohorts, more than 1.38 million people and 112,566 deaths over follow-up periods of 4 to 25 years. In the pooled analysis, short sleep was associated with a higher risk of death, a relative risk of 1.12, and long sleep with a higher one still, 1.30.

A 2017 dose-response meta-analysis by Yin and colleagues in the Journal of the American Heart Association found a U-shaped curve for death and for cardiovascular disease, with the lowest risk at about 7 hours of sleep a day. Above 7 hours, the risk of death rose by a relative 13% for each extra hour; below 7, by 6% for each hour less.

Those numbers sound alarming. They need reading carefully.

Why long sleep may be a sign, not a cause

The AASM and SRS panel examined this literature in detail when they wrote their recommendation. Their discussion paper makes several points that matter:

  • There is little experimental evidence against long sleep. Short sleep has been studied in experiments, where people are kept short of sleep and the effects measured. Long sleep mostly has not. The panel wrote that, given the lack of experimental evidence for harmful effects of long sleep, the observed links with metabolic problems are often interpreted as residual confounding: other factors that travel with long sleep and cause the harm.
  • Illness can cause long sleep. People who are unwell, depressed or in the early stages of a disease often sleep more. The panel noted that the role of medical conditions that could lead to both long sleep and earlier death is unclear, and that the higher risk linked to long sleep may be partly explained by age.
  • The sleep was self-reported. In the Cappuccio studies, sleep duration was measured by questionnaire, and time in bed is easily mistaken for time asleep.

Put together: long sleep is linked with poorer health, but it is quite possible that much of the link runs the other way, with poor health causing long sleep. That is why "too much sleep" is better treated as a question worth asking than as a danger in itself.

Ordinary reasons for a long night

Many long nights are not a problem at all:

  • Repaying sleep debt. After a short week, a long weekend sleep is the body catching up. The AASM names this as a case where more than 9 hours may be appropriate.
  • Being ill. Sleeping more while fighting an infection is normal, and the panel names illness too.
  • Being young. Teenagers need 8–10 hours by both panels' ranges, and the AASM names young adults as a group for whom more than 9 hours may be appropriate. Our guide on how much sleep you need by age has the full table.

Where to pay attention is a steady pattern: regularly needing far more than 9 hours and still waking tired, or a sudden change in how much you sleep without a reason you know of. That is worth raising with a doctor.

Finding your own amount

Inside the 7–9 hour band, need varies from person to person. A useful test is your natural wake time on free days after the first few catch-up mornings, and whether you are sleepy in quiet moments during the day.

The sleep calculator can help you aim for the band rather than overshoot it. It counts in whole 90-minute cycles from your bedtime or back from your alarm, adding 15 minutes to fall asleep: five cycles is about seven and a half hours of sleep, six about nine. Both numbers are planning assumptions you can adjust.

Long nights and dreams

Long sleep has one side effect people often notice: more dreams. NINDS notes that REM periods grow longer later in the night, so a long morning holds more of the dream-rich sleep. That is why a lie-in can end with a vivid, detailed dream. If you want to keep it, write it down before you check your phone; our guide on how to remember your dreams covers the habit, and if the dream is a common one, such as being late, its dictionary entry sets out what the old books and psychologists made of it.