Snoring heavily almost doubles the risk of developing rheumatoid arthritis, a new study shows.

Researchers found patients diagnosed with the snoring-related condition sleep apnoea were nearly twice as likely to suffer the joint-damaging disease.

The discovery, which comes from research carried out in Taiwan, is something of a surprise as rheumatoid arthritis - which affects around 350,000 people in the UK - is thought to be triggered when something goes wrong with the immune system.

The same study found a similar increase in the risk of other so-called autoimmune disorders, where the body's defences start to attack healthy tissues.

Scientists said they believe the explanation lies in the fact that chronic sleep apnoea can lead to inflammation in blood vessels throughout the body, which may act as a catalyst for arthritis.

Although previous studies have suggested sleep apnoea may raise the risk of heart attacks, the latest investigation is the first to show a link with arthritis.

An estimated three million people in Britain suffer with sleep apnoea, though many more may remain undiagnosed.

As sleep begins, the muscles in the airway relax. For most people this does not pose a problem but in sleep apnoea, it leads to a complete collapse which shuts off breathing for at least ten seconds.

It also disrupts breathing and triggers the sound of snoring as air vibrates against the soft tissue that stands in its way.

Once the brain realises breathing has stopped it sends out a signal for the airway muscles to contract again.

This opens the airway and the sufferer normally wakes with a jolt. In mild sleep apnoea, this can happen about once every ten minutes. If it's severe, it means sleep can be disturbed every couple of minutes.

Very few people remember waking up at all because they fall asleep again within seconds.

Yet the cumulative effect is that they feel exhausted during the day, putting them at increased risk of accidents. Being overweight is one of the major risk factors.

In the latest study, by experts at the Taipei Medical University, 1,411 sleep apnoea patients were compared to a 7,000-strong group of healthy adults.

Over a five-year period, researchers monitored how many in each group went on to develop rheumatoid arthritis, ankylosing spondylitis and systemic lupus erythematous - all conditions where the immune system goes haywire and causes swollen, painful joints and flu-like symptoms.

The results, published in the journal Sleep Medicine, showed the snoring-affected group were 91 per cent more likely to develop one of the three conditions.

However, the researchers stressed that the absolute risk of falling ill was still small. Out of the snoring patients, only 2.91 percent experienced arthritis-related problems.

In a report on their findings the researchers said: 'Our study is the first to investigate the association between sleep apnoea and the development of autoimmune diseases.

'We think this may have gone unnoticed in clinical settings because these cases are relatively rare and may not be reported.

'But the potential link between these two conditions should not be overlooked. Among the diseases we studied, rheumatoid arthritis had the highest risk of developing in sleep apnoea patients.'

As well as inflamed and swollen joints, arthritis sufferers also experience flu-like symptoms. In very severe cases, they can end up crippled and unable to live a full life.

But diagnosing the condition can be difficult as the early signs can be as innocuous as a slight stiffness in hand joints, often early in the morning.