'Obesity Paradox' No Help in Trimming Deaths in Diabetes

Marlene Busko

January 16, 2014

BOSTON, MA — In a large study of adults newly diagnosed with type 2 diabetes, those who were overweight or obese did not have a lower risk of dying from CVD, cancer, or other causes, compared with those who had a normal weight[1].

This study is very important because it is the largest one to investigate this relationship between body-mass index (BMI) and mortality and "does essentially conclude that there is no obesity paradox"; it dispels the notion that obesity or overweight provides a survival advantage compared with normal weight among patients with diabetes, lead author Dr Deirdre K Tobias (Harvard School of Public Health, Boston, MA) told heartwire .

They observed a J-shaped relationship between BMI and mortality among all participants. Smokers in the lower-normal BMI range—18.5 to 22.4—had a much higher risk of mortality than patients with a BMI in the upper-normal reference range—22.5 to 24.9—and were more likely to die from cancer. Among nonsmokers, however, as BMI increased, mortality from cancer and CVD also increased, in a linear relationship.

The study showed that "the higher the body weight, the greater the risk of cardiovascular mortality, and again, among smokers, that relationship is less clear, because smokers can be a lot less healthy at those low-BMI categories but also have a very high cardiovascular mortality rate," Tobias noted. It is important for clinicians to address both smoking and weight issues in their patients. "If you have a [patient who is a] smoker in your office, one of the main priorities should be [advising him or her about] quitting smoking; however, maintaining a healthy body weight should also be a component of that intervention."

The study is published in the January 15, 2014 issue of the New England Journal of Medicine.

Is the Obesity Paradox Real?

Previous studies among patients with heart failure, end-stage renal disease, hypertension, and type 2 diabetes have reported that obese patients had a lower risk of mortality than those who had a normal weight. However, most of those studies were small and did not take into account that smoking and preexisting chronic conditions might explain why patients with lower weight were more likely to die, Tobias and colleagues explain.

They conducted a detailed analysis of the association between BMI and risk of death in two large, prospective cohort studies. They analyzed data from 8970 participants from the Nurses' Health Study and 2457 participants and Health Professionals Follow-up Study who were free of cardiovascular disease and cancer when they developed incident diabetes.

At study entry, the participants had a BMI of at least 18.5. The studies were started in 1976 and 1986, and about 54% to 62% of the participants in different BMI categories were current or former smokers. The participants had a mean age of 62 when they were diagnosed with diabetes.

The study subjects replied to surveys every two years, which provided information including weight, smoking status (ever smoked vs never smoked), and new diagnosis of type 2 diabetes. Based on their BMI just prior to being diagnosed with diabetes, they were divided into six categories: 18.5–22.4, 22.5–24.9 (reference), 25.0–27.4, 27.5–29.9, 30.0–34.9, and >35.0.

During a mean follow-up of 15.8 years, there were 3083 deaths: 941 from cardiovascular disease, 784 from cancer, and 1358 from other causes.

There was a J-shaped relationship between all-cause mortality and BMI at the time of diagnosis of diabetes, with the lowest risk among those with a BMI of 22.5 to 24.9.

Linear Relationship Among Nonsmokers, Younger Participants

In addition to differences in the relationship between BMI and mortality among smokers vs nonsmokers, there were differences related to age. As BMI increased, all-cause mortality tended to increase for participants who were diagnosed with diabetes when they were younger than 65. This relationship was not as strong among older participants, possibly due to confounding from coexisting chronic diseases or because BMI may be less valid when individuals have age-related decline in muscle mass. Therefore, care should be taken when interpreting the results from the older participants in this study, the researchers advise.

"The maintenance of a healthy body weight should remain the cornerstone of diabetes management," they conclude. "Because we know that weight loss can be very difficult, prevention of weight gain to begin with among people who are a high risk for diabetes, such as those with prediabetes, should be at the forefront," Tobias added.

The study was supported by grants from the National Institutes of Health and the American Diabetes Association. Tobias has no conflicts of interest. Disclosures for the coauthors are listed on the journal website.

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