Exposure to second-hand smoke can increase a person’s risk of developing glucose intolerance, which is a precursor to diabetes, according to research reported on Friday.

Scientists in the United States found that smokers had the highest risk of developing glucose intolerance but non-smokers who breathed in other people’s smoke were not far behind.

“These findings support a role for both active and passive smoking in the development of glucose intolerance in young adulthood,” said Thomas Houston of the Birmingham Veterans Affairs Medical Center in Alabama.

“We identified passive tobacco exposure in never-smokers as a new risk factor for glucose intolerance,” he added.

People suffering from glucose intolerance have elevated blood sugar levels. They still produce insulin but the amounts are insufficient to control blood sugar levels effectively.

Houston and his team studied the impact of smoking on 4,572 men and women in four American cities over 15 years. Their findings are published online by the British Medical Journal.

Smokers in the study had the highest risk of developing glucose intolerance at 22 percent, compared to 17 percent risk for people who did not smoke but who had been exposed to second-hand smoke.

Non-smokers who had not breathed in others’ smoke had the lowest risk at 12 percent followed by smokers who had given up who had a 14 percent risk.

Whites in the study were more susceptible to the effects of smoking on glucose intolerance than African-Americans, according to the scientists.

They noted that passive smoke contains similar toxins to active smoke but is produced at different temperatures and in different conditions so some toxic substances are even more concentrated in passive smoke.

If one of the concentrated toxins affects the pancreas, which produces insulin, it could explain the findings, they added.

“We found that tobacco exposure is associated with the development of glucose intolerance over a 15 year period, with a dose-response effect apparent,” Houston added.