Among Diabetes Patients, the Obese Outlive the Trim

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People with Type 2 diabetes who are relatively trim may not live as long as people with the condition who carry extra weight, a new study finds.

In the study, people with diabetes who were of normal weight at the time of their diagnosis were about twice as likely to die from any cause over a 10- to 30-year period than those who were overweight or obese at diagnosis.

The findings held even after the researchers took into account factors that could increase people's risk of dying, such as age, blood pressure, blood fat levels and smoking status.

The results agree with the so-called obesity paradox: the idea that, despite being at a higher risk of many chronic conditions, obese people seem to be protected from dying of certain diseases, such as heart disease.

The researches aren't sure why overweight and obese diabetes patients in the study fared better than normal-weight patients in terms of survival, and they said further research is needed.

It's possible that normal-weight people who develop diabetes have genetic variations that put them at risk for other illnesses, too, said study researcher Mercedes Carnethon, an associate professor of preventive medicine at Northwestern University Feinberg School of Medicine.

"Whatever that genetic change or mutation may be may also increase their likelihood of suffering mortality," Carnethon said.

Diabetes and risk of death

Carnethon and colleagues analyzed information from five previous studies that included a total of 2,625 people with diabetes, who were followed for nine to 28 years.

Participants were classified as normal weight if their body mass index was between 18.5 and 24.9, and as overweight/obese if their BMI was 25 or greater.

The proportion of adults in the study who were normal weight at the time of their diabetes diagnosis was 12 percent. Over the course of the studies, a total of 449 people died — 178 from heart disease, and 253 from other causes.

The yearly death rate for normal-weight people was 284.8 per 10,000 people, while it was 152.1 deaths per 10,000 among those who were overweight or obese..

There was no difference between the rate of death from heart disease in normal weight and that of overweight/obese individuals, according to the study.

What should normal-weight diabetics do?

Normal-weight people make up just 5 percent to 15 percent of the diabetic population, Carnethon said. However, because of these people's increased risk of death, doctors should take that population very seriously, Carnethon said.

Older people and those of certain ethic groups, including Asians, are at higher risk for diabetes that occurs at a normal weight, Carnethon said. Cases of normal-weight diabetes are likely to increase as the population ages and diversifies, she said.

Diabetes patients, regardless of weight, are urged to exercise and follow a diet that will help reduce their blood sugar and blood fat levels, Carnethon said. For normal weight people,the goal of these recommendations is not necessarily to lose weight, but rather to help reduce risk factors for disease and death.   

One limitation of the study is that the researchers were not able to measure the study participants' distribution of fat tissue directly. (BMI is a ratio of weight to height.) It could be that some people with a high BMI who are classified as obese actually have a high proportion of lean muscle mass, which is healthier than fat, the researchers said. By contrast, some normal-weight people may have a high percentage of body fat if they have depleted muscle mass.

The study appears in the Aug. 8 issue of the Journal of the American Medical Association.

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