The findings are reported in the Jan. 5 issue of Annals of Internal Medicine.
The authors stress that their findings should not deter people from quitting smoking, which is also a risk factor for heart disease, stroke, atherosclerosis, and cancer. They say that the health benefits of smoking cessation outweigh the short-term risk.
“The message is: Don’t even start to smoke,” Hsin-Chieh Yeh, PhD, an epidemiologist at the Johns Hopkins University School of Medicine and lead author of the study, says in a news release. “If you smoke, give it up. That’s the right thing to do.”
She says smokers who quit “have to also watch their weight” because obesity is tied to diabetes, cardiovascular disease, and other health problems.
Researchers in 1987-1989 enrolled 10,892 middle-aged adults who did not have diabetes and followed them for nine years. The study found that overall, people who smoked had a 42% higher risk of developing diabetes during the follow-up period than nonsmokers. However, smokers who quit had a 70% higher risk of developing type 2 diabetes in the first six years after quitting than people who had never smoked.
The risks of developing type 2 diabetes were highest in the first three years after quitting smoking, then returned to normal after 10 years, the researchers say.
Among those who continued smoking over that period, the chance of developing diabetes was 30% higher than in people who had never smoked.
The study found that people who smoked the most and those who gained the most weight after quitting had the highest likelihood for developing diabetes.
The authors report that new quitters had significant increases in weight, waistline measurement, and fasting blood sugar levels compared with people who had never smoked.
Yeh and colleagues say doctors should remind patients of the benefits of exercise, staying trim, and avoiding smoking.
“For smokers at risk for diabetes, smoking cessation should be coupled with strategies for diabetes prevention and early detection,” the authors write.
They say the study “suggests that heavy smokers with evidence of systemic inflammation who gain substantial weight after quitting are at the highest risk for diabetes.”
"[P]hysicians should be aware of this elevated risk and should consider countermeasures, especially for heavy smokers,” the researchers say.