Obstructive sleep apnoea (OSA) is caused by the muscles and soft tissue in the back of your throat collapsing inwards during sleep. These muscles support your tongue, tonsils and soft palate (a muscle at the back of the throat that is used in speech).

Once the muscles relax, the airway in your throat can narrow or become totally blocked. This interrupts the oxygen supply to your body, which triggers your brain to pull you out of deep sleep so that your airway reopens and you can breathe normally.

Risk factors

There are a number of risk factors for OSA, described below.

• Being overweight is a major risk factor because excessive body fat increases the bulk of soft tissue in the neck, which can place a strain on the throat muscles; excess stomach fat can also lead to breathing difficulties, which can make OSA worse.
• Being male - it is not known why OSA is more common in men than in women, but it may be related to different patterns of body fat distribution.
• Being 40 years of age or more - although OSA can occur at any age, it is more common in people who are over 40 years old.
• Having a large neck - a man of average height (1.7m or 5ft 8in) with a collar size that is greater than 45cm (18 inches) is classed as obese and has an increased risk of developing OSA.
• Taking medicines that have a sedative effect, such a sleeping tablets or tranquillisers.
• Having an unusual inner-neck structure, such as an unusually narrow airway, unusually large tonsils or tongue, or having a small lower jaw that pushes the tongue backwards.
• Having excess folds in the inner lining of the mouth (mucous membrane).
• Alcohol - drinking alcohol can make snoring and sleep apnoea worse.
• Smoking - you are three times more likely to develop sleep apnoea if you smoke.
• Being menopausal - the changes in hormone levels during the menopause may cause the throat muscles to relax.
• Having a family history of OSA - there may be genes inherited from your parents that can make you more susceptible to OSA.
• Diabetes - OSA is three times more common in people with diabetes.
• Nasal congestion - OSA occurs twice as often in people with nasal congestion, which may be due to the airways being narrowed.