Passive smoking increases the risk of developing glucose intolerance - a precursor to diabetes, according to a new study.

The US research also shows that overall, white Americans are more susceptible to this effect than African-Americans.

Researchers examined 4,572 men and women in four US cities, dividing them into four categories of smoking status: ranging from those who smoked, to those who had neither smoked nor breathed in other people’s smoke.

The study focussed only on those who were white or African-American.

The researchers then tracked how many participants developed glucose intolerance - where the body can no longer produce enough insulin to regulate blood sugar - over a 15-year period.

The study found that smokers had the highest risk, with 22 per cent of them getting the disease over the study period.

Non-smokers who had no exposure to passive smoke had the lowest risk, with less than 12 per cent developing the condition.

But 17 per cent of those who had never smoked themselves but were subject to passive smoke also developed glucose intolerance - higher than the 14 per cent risk rate in the group who had previously smoked and given up.

"Those breathing second-hand smoke are exposed to many toxins," said lead researcher Thomas Houston, of Birmingham Veterans Affairs Medical Center, Alabama.

"And the chemical reactions which produce second-hand smoke mean that some of those toxins may be at even higher concentrations than the levels breathed in directly by smokers.

"If one of these toxins particularly affects the pancreas - the organ which produces insulin - this may explain the findings.

"Until now, it had not been known that those breathing second-hand smoke faced an increased risk of diabetes. More studies are now needed."

Diabetes remains a leading cause of heart disease, stroke, blindness, kidney disease and amputations.

According to the Centers for Disease Control and Prevention, 21 million people in the US have the disease.

Since 1987, the death rate due to diabetes has increased by 45 per cent, while the death rates due to heart disease, stroke and cancer have declined.

There are two main types of diabetes, Type 1 diabetes and Type 2.

Type 1 diabetes - also known as insulin-dependent - results from the body's failure to produce insulin.

Type 2 diabetes develops when the body can still make some insulin, but not enough, or when the insulin that is produced does not work properly.

The study findings are published in the British Medical Journal.