Contrary to a popular theory, adults who are overweight when they are diagnosed with diabetes are not protected against dying early, a large new study shows.
The findings call into question what's known as the "obesity paradox," the belief that people with a normal weight are more likely to die from type 2 diabetes than those who are overweight or obese.
"There's been a pretty polarized debate over whether this is real or not," lead author Deirdre Tobias, from the Harvard School of Public Health in Boston, told Reuters Health. "I would like to believe that this lays it to rest."
The results, she said, show that, "There is no benefit of being overweight or obese. In fact, we see that, among non-smokers at least, being overweight and obese does increase your risk. It's not neutral."
Tobias and her colleagues analyzed data from two large, long-term studies: the Nurses' Health Study, begun in 1976, and the Health Professionals Follow-up Study, inaugurated in 1986. The new report included more than 11,000 people in those studies who were diagnosed with diabetes. None of them had cancer or heart disease at the time of diagnosis.
Volunteers were followed for nearly 16 years, on average. During that time, about 3,000 of them died.
The researchers found that people who were overweight or obese when they were diagnosed with diabetes were between nine and 33 percent more likely to die than those who were diagnosed while at the higher end of normal weight. The risk was greatest among the heaviest participants.
People diagnosed with diabetes before age 65 faced a higher risk as their weight rose. In those 65 and over, the effect was less pronounced, according to findings published Wednesday in the New England Journal of Medicine.
Smoking was also linked to when people died. For instance, the lowest-weight women with a history of smoking were more likely to die during the study period than normal-weight women who smoked. Risks then increased again at higher weights.
Among non-smokers with diabetes, however, the trend was more direct: the lower a person's weight, the lower the risk of early death.
"I thought it was interesting that being a thin smoker wasn't healthy," Dr. Susan Spratt, a diabetes researcher from the Duke University School of Medicine in Durham, North Carolina, told Reuters Health.
"Smoking might keep your weight down but you have more risk," Spratt, who was not involved in the new research, said. "Smoking compounds all the obesity complications, whether it's diabetes or heart disease."
One earlier study had concluded that people who had a normal weight when they were diagnosed with diabetes were twice as likely to die over a given period as overweight or obese people.
The researchers said one problem with past studies suggesting that extra weight is protective in diabetes is that weight estimates were often done decades after the diagnosis, which could skew the results.
"We were also able to control for smoking status better," Tobias said. That's important because smokers tend to be leaner than non-smokers.
"Losing weight is beneficial, and you may not have to lose a lot," Spratt said. "But losing five percent or 10 percent of your body weight if you are obese can help so many issues, from joint pain and sleep apnea, to diabetes and diabetes complications."
SOURCE: bit.ly/Kctu9D New England Journal of Medicine, online January 15, 2014.