Sleep apnoea and weight: the two-way problem

Obstructive sleep apnoea (OSA) and excess weight feed each other. Fat around the neck and upper airway narrows the space available to breathe through at night. The resulting broken sleep raises appetite, lowers energy and makes losing weight harder. Round it goes.

The useful thing about a loop is that you can break it at either end.

What happens during an apnoea

During sleep, the muscles holding the upper airway open relax. In OSA the airway narrows or closes completely, breathing stops for ten seconds or more, oxygen falls, and the brain briefly wakes you enough to reopen it. You usually have no memory of this.

It can happen five times an hour. It can happen sixty. Severity is measured by the apnoea-hypopnoea index (AHI) — events per hour of sleep:

• 5–14: mild
• 15–30: moderate
• over 30: severe

The signs

• loud, habitual snoring
• pauses in breathing, gasping or choking, usually noticed by a partner
• waking unrefreshed however long you were in bed
• heavy daytime sleepiness, particularly when sitting still or driving
• morning headaches, dry mouth
• needing to pass urine several times a night

The last one surprises people. It is common enough to be a useful clue.

How much does weight matter?

A lot. A long-running cohort study found that a 10% gain in weight predicted a 32% increase in AHI, and a 10% loss predicted a 26% decrease ^[3]. Few relationships in medicine are that linear.

More recently, the SURMOUNT-OSA trials tested tirzepatide in adults with obesity and moderate-to-severe OSA. Apnoea events fell by around 25 to 29 per hour, against roughly 5 per hour on placebo, and around half of participants reached the point where their apnoea was considered resolved or minimal ^[2]. That is a large effect for a drug not designed for the airway.

It is worth being clear about what that does and does not mean. It shows that weight loss of that magnitude changes OSA substantially. It does not mean medication replaces diagnosis and treatment — you still need a sleep study, and CPAP remains the first-line treatment for moderate to severe disease.

Treatment, briefly

CPAP — a mask delivering gentle positive pressure that splints the airway open. Highly effective when used consistently. It treats the apnoea, not the weight; trials have not shown it causes weight loss by itself. What it often does is return enough energy to make other changes possible.

Mandibular advancement devices — a custom dental appliance that holds the lower jaw forward. An option in mild to moderate disease or where CPAP is not tolerated.

Positional measures — some people’s apnoea is far worse on their back.

Weight loss — reduces severity, and in some people resolves it.

Alcohol and sedatives — both relax the airway muscles further. Reducing them helps.

Driving

This matters legally as well as medically. If you have excessive sleepiness that is likely to impair driving, you must not drive, and OSA syndrome causing excessive sleepiness is notifiable to the DVLA ^[5]. Most people can return to driving once treated and symptoms are controlled.

When to speak to a clinician

Ask for assessment if you:

• snore loudly and someone has witnessed you stop breathing, gasp or choke
• fall asleep unintentionally during the day, particularly while driving
• wake with headaches or a very dry mouth most mornings
• have high blood pressure that is hard to control
• have a collar size of 17 inches or more with any of the above

Do not drive if you are excessively sleepy. Referral is usually to a sleep clinic for a home sleep study.

This article is for general information and isn’t a substitute for advice from your own clinician. If you feel unwell, contact your GP or NHS 111. In an emergency, call 999.