Previous studies have already indicated a direct link between smoking and diabetes, which can cause life-threatening complications such as heart and kidney disease, blindness and amputations.

But this is the first research to show passive smoking can increase susceptibility to the disease.

Risk of Glucose Intolerance

The US study, published online in the British Medical Journal, examined 4,500 patients over 15 years.

At the start of the study, the men and women aged 18 to 30 were classified in four ways: as smokers, those 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 percent affected during the study period.

The next group most at risk was those who had never smoked themselves but had breathed in secondhand-smoke, with 17 percent developing glucose intolerance over the 15 years.

Non-smokers who had never been exposed to second-hand smoke had the lowest risk, with 12 percent developing the condition. For those who had previously smoked and given up, the figure was 14 percent.

Blindness, Heart Disease, Amputation

More than two million Britons have been diagnosed with type 2 diabetes, the kind which tended to strike in midlife but is increasingly occurring at younger ages.

It is expected the toll will reach three million by 2010 unless there is a move to eat less and take more exercise.

Zoe Harrison, Care Adviser at Diabetes UK, said: "We already know that smoking or even being in a smoky atmosphere is bad for us. If we needed another reason for banning smoking in public places, the risk of blindness, heart disease and amputation that can be caused by Type 2 diabetes should be pretty compelling. If this pattern continues, we will soon start seeing people losing their sight or having amputations at a much younger age."