Short sleep and weight: what the research shows

Adults who regularly sleep less than seven hours a night have a higher risk of obesity than those who sleep longer. The Sleep Health Foundation describes the evidence for this link as good and drawn from many studies. It also reports that losing weight is more difficult for people who sleep for short periods.

The mechanism appears to run mostly through eating. Tired people eat more, and the extra is not matched by any rise in the energy they use. Researchers still disagree about exactly why.

What happens to appetite

The best-known explanation involves two hormones. Leptin helps to control appetite, and ghrelin is thought to stimulate food intake. In a study of 1,024 people from the Wisconsin Sleep Cohort, summarised in PLoS Medicine in 2004, short sleep was associated with low leptin and high ghrelin. Among the participants who slept less than eight hours, body mass index rose as sleep duration fell.

That account has since been questioned. A 2014 review in Frontiers in Endocrinology agreed that restricting sleep makes people eat more. It pointed out, however, that when volunteers in sleep experiments were given free access to food, the hormone changes generally did not appear. The reviewers argued that the extra eating is driven more by reward than by hunger. People who are short of sleep snack more, eat more often and lean towards energy-dense foods, and the amount eaten goes up with the number of hours spent awake.

The Sleep Health Foundation's fact sheet covers both ideas. Short sleep disrupts leptin and ghrelin, it says, and also affects the areas of the brain that process reward, which could lead to seeking out food. More time awake means more time to eat, including late into the night, when the body metabolises food less effectively. Fatigue then reduces the motivation to exercise and to choose food well.

How much extra

Researchers at King's College London put a figure on it in a meta-analysis published in the European Journal of Clinical Nutrition in 2017. They pooled 11 experiments, involving 172 people, in which sleep was partly restricted. After short sleep, participants ate an average of 385 kilocalories more a day than after normal sleep, which is roughly 1,600 kilojoules. There was no significant change in the energy they used. The extra intake came with more fat and less protein.

The limits of that finding matter. The total number of participants was small, and these were experiments, not a record of ordinary life over years. The authors' conclusion is careful: an energy surplus of this kind may contribute to weight gain in the long term. They begin the paper by saying it is unknown whether short sleep causes weight gain.

How common short sleep is

An estimated 39.8% of Australian adults experience some form of inadequate sleep, according to Asleep on the Job, a report commissioned by the Sleep Health Foundation and based on 2016–17 figures.

The foundation's guidance is that most adults of all ages need seven to nine hours. Getting older does not reduce the requirement.

Habits the Sleep Health Foundation recommends

The foundation's fact sheet on good sleep habits is realistic about timing. Improvement does not come as soon as changes are made. It comes when the habits are kept up on most days.

• Keep regular hours. Go to bed and get up at about the same time each day. The body clock works best with a routine.
• Wind down for an hour. Emails, television and important discussions are best avoided in the hour before bed. Screens ideally go off one to two hours beforehand and stay out of the bedroom.
• Watch the caffeine. Views differ on timing. Some advise avoiding caffeine for at least three to seven hours before sleep, others suggest none after lunch for people with sleep problems.
• Go easy on alcohol. It may help with falling asleep but makes it harder to stay asleep, and it makes snoring and sleep apnoea worse.
• Time the evening meal. Finish dinner at least two hours before bed. Going to bed hungry does not help either, and some people sleep better after a small snack.
• Get daylight and exercise. Being outside in natural light, ideally early in the day, improves sleep at night. Exercise helps too, though not just before bed.
• Do not lie there awake. If sleep has not come within 20 to 30 minutes, get up, sit quietly in another darkened room without a screen, and go back to bed when sleepy.
• Do not overstay. Many poor sleepers spend too long in bed. The foundation suggests no more than about eight hours.

When to raise it with a GP

Weight and sleep also affect each other through obstructive sleep apnoea, in which the throat repeatedly narrows or closes during sleep. Obesity is the main risk factor, the Sleep Health Foundation says, and the relationship appears to run both ways. Sleep apnoea may itself promote weight gain, and some studies show that people with the condition lose less weight in long-term weight loss programs than people without it.

Snoring is worth mentioning to a GP when it comes with any of the following: a partner noticing pauses in breathing, waking up gasping or choking, sleep that does not refresh, or a struggle to stay awake in the afternoon. A person can have the condition without knowing. Women's symptoms can also look different. The foundation notes that women may have trouble falling and staying asleep, low mood and fatigue, while men more often present with loud snoring and marked daytime sleepiness.

The reasons to follow it up go beyond weight. People with obstructive sleep apnoea are about two and a half times more likely to have a motor vehicle accident. Untreated moderate to severe sleep apnoea is associated with a higher risk of high blood pressure, heart attack, stroke and diabetes. A GP can refer for an overnight sleep study, which measures sleep, breathing and oxygen levels, and good treatments are available. For some people with a mild form and few symptoms, the foundation says that losing weight, drinking less alcohol in the evening or changing sleeping position may be all that is needed.

The same goes for sleep that stays poor for no obvious reason. If the habits above have been given a fair trial and nothing has changed, the foundation's advice is to see a GP.

None of this means an extra hour in bed will move the scales. The research shows that short sleep goes with more eating and a higher risk of obesity. It has not shown that sleeping longer produces weight loss. What it does suggest is that sleep belongs in the plan next to food and movement.

Sources

1. Sleep Health Foundation, Obesity and Sleep.
2. PLoS Medicine (2004), Sleep Duration Affects Appetite-Regulating Hormones.
3. Chaput J-P, St-Onge M-P, Frontiers in Endocrinology (2014), Increased Food Intake by Insufficient Sleep in Humans: Are We Jumping the Gun on the Hormonal Explanation?
4. Al Khatib HK, Harding SV, Darzi J, Pot GK, European Journal of Clinical Nutrition (2017), abstract via King's College London research portal, The effects of partial sleep deprivation on energy balance: A systematic review and meta-analysis.
5. Sleep Health Foundation, Asleep on the Job: Costs of Inadequate Sleep in Australia.
6. Sleep Health Foundation, Sleep Hygiene: Good Sleep Habits.
7. Sleep Health Foundation, Obstructive Sleep Apnoea (OSA).