Middle-aged adults who quit smoking may see their risk of type 2 diabetes increase for several years - at least partly because of the weight gain that can come with quitting, researchers reported Monday.

The researchers, from Johns Hopkins University in Baltimore, stress that the findings should not discourage anyone from quitting cigarettes.

Rather, they say that smokers and their doctors should work on ways to prevent excessive weight gain as they attempt to quit.

Moreover, the study found, continued smoking is no way to stave off diabetes. Study participants who kept up the habit had a greater long- term risk of diabetes than those who had never smoked.

“The message is: Don’t even start to smoke,” lead researcher Dr. Hsin- Chieh Yeh, an assistant professor of general internal medicine and epidemiology at Hopkins, said in a news release from the university.

“If you smoke,” she added, “give it up. That’s the right thing to do. But people have to also watch their weight.”

The findings, reported in the Annals of Internal Medicine, are based on almost 11,000 initially diabetes-free middle-aged adults who were followed for nine years. During that time, 1,254 developed type 2 diabetes.

Overall, the one-third of tobacco users who smoked most heavily - the equivalent of at least a pack per day for 30 years - were 42 percent more likely to be diagnosed with diabetes than people who had never smoked.

The finding is in line with those from a number of past studies. It’s thought that smoking may promote type 2 diabetes by causing chronic inflammation throughout the body; inflammation may, for instance, make body tissues more likely to become resistant to the blood sugar-regulating hormone insulin, which leads to type 2 diabetes.

However, when Yeh’s team looked at smokers who quit during the study period, they found that not only did the diabetes risk not go away, it increased in the short term.

The risk was greatest in the first three years after quitting, when it was nearly double that of men and women who had never smoked. Those odds gradually decreased over time, with the excess risk disappearing after about a decade.

Weight gain partly explained the diabetes risk associated with quitting, according to Yeh’s team. Systemic inflammation - as measured by the study participants’ white blood cell counts - also appeared to be at work, the study found.

Like smoking, obesity is believed to promote systemic inflammation. The researchers say their findings suggest that heavy smokers who gain a substantial amount of weight when they quit may be at greatest risk of developing diabetes.

To help reduce that risk, Yeh and her colleagues advise doctors to offer lifestyle counseling and “aggressive weight management” help to patients who are quitting smoking.

They also suggest that quitters consider nicotine replacement therapy - which seems to “blunt” the weight gain associated with smoking cessation - and have their blood sugar checked regularly to detect diabetes early.

SOURCE: Annals of Internal Medicine, January 5, 2010.