People who give up smoking are prone to developing diabetes because they gain weight, scientists warn.
A large American study found that people who quit were twice as likely as continuing smokers and up to 70pc more likely than non-smokers to have type 2 diabetes within six years.
The researchers, from Baltimore, said that people attempting to quit should be offered advice on diet and exercise to avoid gaining weight.
But the dangers of developing lung cancer or other health problems from smoking outweigh the short-term risks from quitting and should not be used as an excuse not to kick the habit, they said.
The study enrolled 10,892 middle-aged adults who did not yet have diabetes, from 1987 to 1989. They were monitored for up to 17 years and data about diabetes status, glucose levels and weight were collected.
It is estimated that there are 200,000 persons with Type 2 diabetes diagnosed in Ireland. It is suspected that there are probably 100,000 as yet undiagnosed. Type 2 diabetes normally occurs in middle age and is associated with being overweight.
It is distinct from the Type 1 form of the condition, which is usually diagnosed in children and is managed with daily insulin injections.
In the study, scientists found that people who quit smoking had a higher risk of developing type 2 diabetes in the first six years without cigarettes compared with people who never smoked.
The risks were highest in the first three years after quitting and returned to normal after ten years.
On average, over the first three years of the study, people who stopped smoking put on nearly 8.5lbs (3.8kg) and saw their waist bulge by about 1.5in (3.17cm).
Professor Hsin-Chieh Yeh, the lead author of the study, published in the journal Annals of Internal Medicine, pointed out that cigarette smoking was also a risk factor for type 2 diabetes.
Among those who continued smoking, the risk was lower than in those who quit, but the chance of developing diabetes was still 30pc higher compared with those who had never smoked.
"The message is: don't even start to smoke," she said. "If you smoke, give it up. That's the right thing to do. But people have to also watch their weight."
More than one in four people are still smoking in Ireland, despite the New Year push for them to quit. Research in this country reveals the average smoker goes through 13 cigarettes a day, shelling out around €163.80 each month.
A quarter of those completeing health checks online admit to smoking with a higher proportion -- 24pc -- being female, compared to 21pc of males who smoke.
Natasha Marsland, care adviser at the health charity Diabetes UK, said: "On no account should people use the theoretical results of this study as an excuse not to give up smoking. The health benefits of giving up smoking far outweigh the risk of developing type 2 diabetes from modest, short-term weight gain.