How much sleep you need

An expert panel convened by the National Sleep Foundation reviewed the research and recommends 7–9 hours a night for adults aged 18 to 64, and 7–8 hours for adults aged 65 and older. ¹ The panel also noted that some healthy people sleep a little outside these ranges, while straying far from them is rare. ¹

The American Academy of Sleep Medicine and the Sleep Research Society reached a similar answer for adults aged 18 to 60: seven or more hours a night, on a regular basis. ² They set no upper limit, and said that more than nine hours can be appropriate for young adults, for people recovering from sleep debt and for people who are ill. ²

These are ranges, which leaves room for you. If you wake without an alarm on most days and feel clear-headed through the afternoon, you are probably close to your own number. Our sleep tool, How much sleep do you need?, turns your age and wake time into a bedtime window you can try for a week.

Why short sleep catches up with you

Regularly sleeping less than seven hours is associated with weight gain and obesity, diabetes, high blood pressure, heart disease and stroke, depression and a higher risk of death. ² It is also linked to poorer performance, more errors and a greater risk of accidents. ²

Most of this evidence comes from observational studies. They show that short sleep and poor health tend to travel together, and they cannot prove that one causes the other. The pattern is consistent enough that sleep belongs next to movement and food as one of the basics of a long, strong life.

For people who train hard, sleep is also the quiet half of the plan. The hours you spend recovering are the hours your body has to make use of the work you did.

Rhythm matters as much as hours

A study of about 61,000 UK Biobank participants measured sleep with wrist-worn devices and scored how regular each person's sleep and wake times were from day to day. ³ People with more regular sleep had a lower risk of dying during follow-up, and regularity predicted mortality more strongly than sleep duration did. ³ It is an observational study, so it shows an association rather than proof.

Regularity is also one of the easiest levers to pull. Your body clock takes its timing from light reaching your eyes, and it is synchronised to the solar day. ⁴ A steady daily shape gives it a clear signal to follow.

• Keep your wake time close to the same every day, weekends included.
• Let your bedtime follow from your wake time, and adjust it slowly.
• If you are short on sleep, try an earlier night before you reach for a long lie-in.

Light, caffeine and the evening

Light works in both directions. Your clock is synchronised by light through your eyes, and artificial light at night can alter your rhythm and your sleep. ⁴ In practice, that means getting outside in daylight early in the day and keeping your evenings dim.

Caffeine lasts longer than it feels. In a small sleep study, 400 mg of caffeine taken six hours before bed still reduced measured sleep by more than an hour, and the participants did not notice the difference themselves. ⁵ The authors suggest avoiding substantial caffeine for at least six hours before bedtime. ⁵ The dose in the study was high, so treat six hours as a sensible starting point and find your own cut-off.

A cool, dark and quiet bedroom and a short wind-down without screens give the end of your day a clear edge. Small rituals help here: the same lamp, the same book, the same order of things.

When to talk to a doctor

If you have struggled to fall asleep or stay asleep for months and it affects your days, speak to your doctor. For chronic insomnia in adults, the American College of Physicians recommends cognitive behavioral therapy for insomnia (CBT-I) as the first treatment. ⁶ CBT-I works on sleep timing, habits and the worries that keep you awake.

Sleeping pills may be considered when CBT-I alone has not helped, after a conversation with your doctor about the benefits, harms and costs. ⁶

Loud snoring, pauses in breathing that someone else notices, or waking up gasping or choking can be signs of obstructive sleep apnea. ⁷ These signs deserve a proper sleep evaluation, because questionnaires on their own are not enough to diagnose it. ⁷

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