Sleep for executives: how much you need, and how training helps

What seven hours means

The recommendation refers to sleep, not time in bed. Someone who is in bed from midnight to seven and takes twenty minutes to fall asleep, with a few awakenings, has slept about six and a quarter hours.

The consensus statement adds that sleeping more than nine hours may be appropriate for young adults, for people recovering from a sleep debt and for those who are ill. Need varies between individuals, within a range that for most adults lies between seven and nine hours.

The United States National Heart, Lung, and Blood Institute gives the same figure, and notes that sleep deficiency builds up: an hour lost each night amounts to seven by the end of the week. The calculator above makes that sum for your own week.

The illusion of coping

In laboratory studies where people are restricted to six hours a night for two weeks, their performance on tests of attention declines steadily, to levels comparable with a night of total sleep deprivation. Their own rating of how sleepy they feel rises for a few days and then levels off. They believe they have adapted. Their results show they have not.

For work that consists of judgement, the consequence is practical. Short sleep degrades exactly the faculties that are hardest to notice losing: weighing risk, reading other people, resisting the first plausible answer.

What short sleep does to training and weight

• Appetite. Sleep restriction shifts the hormones that regulate hunger and increases the appeal of energy-dense food. People eat more the day after a short night. See calorie needs.
• Recovery. Much of the repair that follows training takes place during sleep.
• Injury and effort. A given session feels harder, coordination is poorer and motivation lower.
• Blood sugar. Even a few short nights reduce insulin sensitivity in healthy adults.

After a night of under six hours, keep the session and lower the intensity. See exercise and stress for a way to decide.

How exercise improves sleep

People who exercise regularly fall asleep faster and report better sleep. A systematic review of randomised trials found that chronic resistance exercise improves all aspects of sleep, with the largest effect on sleep quality. Aerobic exercise has similar effects.

The timing matters less than is often claimed. Moderate exercise in the evening does not harm sleep in most people. Very hard sessions ending less than an hour before bed can delay it, because core temperature and arousal remain high. If the evening is your only slot, finish at least ninety minutes before bed and keep the last part of the session easy.

The habits that carry the most weight

1. A fixed wake-up time, seven days a week. It anchors the body clock more effectively than a fixed bedtime.
2. Daylight in the morning. Ten to twenty minutes outdoors soon after waking.
3. Caffeine stopped by early afternoon. See caffeine.
4. Alcohol finished three to four hours before bed, or not taken. It fragments the second half of the night. See alcohol and training.
5. A cool, dark, quiet room. In the Gulf, that means air conditioning set low enough and blackout curtains.
6. Screens and email put away thirty to sixty minutes before bed. The light matters less than the content: one message can cost an hour.
7. A short written list of tomorrow's open questions, made before leaving the desk, so that they are not rehearsed at midnight.

Recovering from a short week

Sleeping longer at the weekend repays part of a debt and improves how you feel. It does not fully reverse the effects of the week, and a large shift in waking time on Saturday and Sunday makes Monday harder, a pattern sometimes called social jet lag.

A workable compromise is to rise no more than an hour later than usual at the weekend, and to add a nap of twenty to thirty minutes in the early afternoon. Naps longer than that leave grogginess and reduce sleep pressure at night.

Travel

Crossing time zones disrupts sleep by shifting the body clock away from local time. The measures are specific and covered in jet lag and training.

When it is not a matter of habit

Loud snoring with pauses in breathing, waking unrefreshed whatever the hours, and falling asleep in meetings or at the wheel point to obstructive sleep apnoea, which is common, underdiagnosed and treatable. It is more frequent in men, with age and with abdominal weight. See waist-to-height ratio.

Insomnia lasting more than three months also warrants a consultation. The treatment with the best evidence is a structured behavioural therapy, not medication.

What to track

A wearable gives a reasonable estimate of total sleep time and a poor estimate of sleep stages. Follow two numbers: the average duration over the week, and the regularity of your waking time. A resting pulse that is higher than usual in the morning is a third signal that the night did not do its work. See resting heart rate.

Persistent sleep problems are a medical matter. Sleeping tablets and sedatives should be taken only on medical advice.