A sleep disorder that can leave people gasping for breath at night could be linked to the amount of fat on their tongues, a study suggests.
When sleep apnoea patients lost weight, it was the reduction in tongue fat that lay behind the resulting improvements, researchers said.
Larger and fattier tongues are more common among obese patients.
But the Pennsylvania team said other people with fatty tongues may also be at risk of the sleep disorder.
The researchers now plan to work out which low-fat diets are particularly good at slimming down the tongue.
"You talk, eat and breathe with your tongue - so why is fat deposited there?" said study author Dr Richard Schwab, of Perelman School of Medicine, Philadelphia.
"It's not clear why - it could be genetic or environmental - but the less fat there is, the less likely the tongue is to collapse during sleep."
Sleep apnoea is a common disorder that can cause loud snoring, noisy breathing and jerky movements when asleep.
It can also cause sleepiness during the day, which can affect quality of life.
The most common type is obstructive sleep apnoea, in which the upper airway gets partly or completely blocked during sleep.
Those who are overweight or who have a large neck or tonsils are more likely to have the condition.
How to help sleep apnoea
- Try to lose weight if you are overweight
- Sleep on your side - try a special pillow to help
- Give up smoking
- Do not drink too much alcohol, especially before bed
- Don't take sleeping pills unless recommended
More serious sleep apnoea may need treatment from a sleep clinic. This can include using a CPAP machine, which gently pumps air into a mask over the mouth and nose during sleep, holding the airways open.
Source: NHS UK
Researchers at the Perelman School of Medicine, University of Pennsylvania, scanned 67 people with obstructive sleep apnoea who were obese and had lost 10% of their body weight, improving their symptoms by 30%.
By looking at the size of patients' upper airway structures, the research team was able to find out what changes had driven the improvements.
The patients' weight loss also led to a reduction in the size of a jaw muscle that controls chewing and muscles on either side of the airway, which also helped.
"Now that we know tongue fat is a risk factor and that sleep apnoea improves when tongue fat is reduced, we have established a unique therapeutic target that we've never had before," said Dr Schwab.
The study is published in the American Journal of Respiratory and Critical Care Medicine.
"We know that weight loss is important as it can help to reduce upper airway narrowing," says Dr Nick Hopkinson, medical director at the British Lung Foundation.
"This research adds some information about the exact mechanisms involved, but there aren't any ways to reduce tongue fat specifically so it doesn't seem to have any immediate practical implications for people with the condition."