Passive smoking increases the risk of developing diabetes, a study suggests.
A 15-year US study of 4,572 people backed earlier claims that smokers were at higher risk of developing glucose intolerance - a precursor to diabetes.
But it also found people subject to second-hand smoke had a slightly higher risk of diabetes.
The study, published in the British Medical Journal, suggests smoke toxins could affect the pancreas, which makes the blood sugar regulator insulin
The researchers, led by Professor Thomas Houston of the Birmingham Veterans Affairs Medical Centre in Alabama, divided their subjects into smokers, former smokers, passive smokers and those never exposed to smoke.
They then tracked down how many had developed glucose intolerance.
They found smokers faced the highest risk, with 22% getting the condition over the 15-year period.
Current smokers were defined as those who smoked at least five cigarettes a week for at least three months.
But 17% of those who never smoked themselves, but had been subject to second-hand smoke, went on to develop the condition.
This compared to the 12% of those not exposed to smoke who, the study said, developed glucose intolerance.
The authors said passive smokers are exposed to toxins similar to those of active smokers, but some toxic substances are even more concentrated in passive smoke.
They suggest that if one of these is linked to the poisoning of the pancreas then it might explain the increased risk amongst passive smokers.
They conclude: "We identified passive tobacco exposure in never smokers as a new risk factor for glucose intolerance.
"If confirmed by further research, these findings provide further documentation of the deleterious effects of tobacco smoking, and policy makers may use them as additional justification to reduce exposure to passive smoking."
Zoe Harrison, care adviser at Diabetes UK, said it was already known that smoking or 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.
"Diabetes is already increasing at an alarming rate and lifestyle factors definitely play a huge role in this. If this pattern continues, we will soon start seeing people losing their sight or having amputations at a much younger age," she added.
Neil Rafferty, a spokesman for the pro-smoking group Forest, said there were many causes of diabetes.
"There are so many conflicting reports about the effects of passive smoking, we maintain, that there is no conclusive evidence that there are any affect on health."
However, he said no one should be forced to take in second hand smoke - which was why the group advocated segregated areas for those who did not what to be exposed.
There is a wide consensus among doctors that passive smoking is bad for health, although a paper published in the British Medical Journal did raise doubts about the link.