Passive smoking can increase the risk of developing diabetes, scientists have warned.

Research shows that breathing other people's smoke increases the risk of developing glucose intolerance, the precursor to diabetes. It is already known that smokers can have a higher risk of developing the disease, but scientists say this is the first time a link with passive smoking has been established.

The US study, published in the online version of the British Medical Journal, assessed 4,572 men and women aged 18 to 30 for 15 years. They divided the people into four categories: smokers; people who had given up; those who had never smoked but had been exposed to second-hand smoke; and those who had never smoked and had never been exposed to second-hand smoke.

After examining the results, the researchers found that smokers had the highest risk of developing glucose intolerance - where the body can no longer produce enough insulin to regulate blood sugar - with 22 per cent of them getting it over the study period.

The next group most at risk comprised those who had never smoked but had breathed in second-hand smoke - with 17 per cent developing intolerance over the 15 years.

Non-smokers who had never been exposed to second-hand smoke had the lowest risk, with 12 per cent developing the condition.

For those who had previously smoked and given up, the figure was 14 per cent.

The research was led by Dr Thomas Houston at the Deep South Centre on Effectiveness Research in Alabama.