Normal-weight people who are diagnosed with type 2 diabetes have more than twice the risk of dying from heart disease and other causes than their overweight peers with the disease, a new analysis indicates.
Although type 2 diabetes is normally associated with people who are overweight and lead sedentary lifestyles, the metabolic disorder can affect those who are normal weight. In the study, about one in eight people diagnosed with type 2 diabetes were of normal weight - and it appears the disease may be more aggressive in people who aren't overweight when they're diagnosed.
"We were somewhat surprised to find that people who have type 2 diabetes who were normal weight at the time of diagnosis had higher rates of mortality than those who were overweight or obese," said study author Mercedes Carnethon, associate professor of preventive medicine at the Feinberg School of Medicine at Northwestern University in Chicago.
"Overweight and obesity confers certain protective effects in end-stage renal disease and heart failure. It's called the obesity paradox," Carnethon explained. She added, however, that being overweight or obese is far more harmful than protective overall.
How the study was done
Extra weight is associated with the development of many diseases, such as type 2 diabetes, heart disease and some cancers. People who have type 2 diabetes and are overweight still have an elevated risk of complications, and one of the most effective treatments for type 2 diabetes is to lose weight.
Results of the study appear in the Journal of the American Medical Association.
The analysis included five long-term studies done from 1990 to 2006. The research looked at more than 2 600 people who were diagnosed with diabetes. Half of the study participants were male. All were over age 40, and about two-thirds were white.
Weight status was measured using the body-mass index, a measure of body fat based on height and weight. A BMI of 18.5 to 24.99 is considered normal weight, while anything over 25 was considered overweight or obese.
Depending on the study, between 9 percent and 21 percent of participants were normal weight when diagnosed with diabetes. Overall, 12% of the study participants were normal weight at diagnosis.
Nearly 450 people died during the study - 178 from cardiovascular disease and 253 from other causes. Another 18 died of unknown causes.
What the study found
After the researchers adjusted the data to control for factors such as waist circumference, smoking status, demographic factors and blood pressure and cholesterol levels, they found that people who were normal weight when diagnosed with type 2 diabetes had more than twice the risk of dying from heart disease than their overweight counterparts. They also had a 2.32 times higher risk of dying from any other cause compared to their overweight peers.
Although the study suggests an association between weight and death risk among those with type 2 diabetes, it does not establish a cause-and-effect link between the two.
Carnethon said it is not clear why normal-weight people have a higher risk of dying. She said it may be that the genetic profile in thinner people who develop type 2 may be different. It also may be that some doctors don't treat type 2 diabetes in thinner people as aggressively as they do in heavier people, or that the available treatments don't work as well in thinner people.
"Type 2 diabetes is bad in everyone, but this study shows it may be worse in non-obese people. They may have a different genetic component," said Dr Joel Zonszein, director of the Clinical Diabetes Center at Montefiore Medical Center in New York City. "Or it could be that BMI isn't as reliable a test for mortality risk in people who have a lower BMI as it is for those with a higher BMI."
The bottom line, Carnethon said, is that "type 2 diabetes in the absence of obesity doesn't mean a lower risk of bad outcomes. Right now, about 5 percent to 15 percent of people with type 2 diabetes are normal weight, and that proportion overall is going up. Physicians need to take this group seriously and treat them as aggressively."
Carnethon recommended exercise - particularly resistance training - as a good way for thinner people with type 2 diabetes to lower their blood sugar. Exercise is also quite helpful in lowering blood sugar levels for people who are overweight with type 2 diabetes - as is losing weight.
Diabetes and diet
Learn more about type 2 diabetes from the National Institute of Diabetes and Digestive and Kidney Diseases.
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