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Study of BMI, Death Rates Over Time Debunks "Obesity Paradox"

Mary Caffrey
The new study shows that looking at a person's body mass index over an extended period gives a fuller picture of the relationship between excess weight and mortality.
A new study that tracked weight and death rates for more than a decade has found that being obese does raise the risk of an early death—in contrast with other research that found those who were obese were at less risk.

The so-called “obesity paradox” has confounded researchers and raised alarms among those in public health, who feared that warnings about being overweight would not be taken seriously. This new study, involving researchers from Boston University and the Harvard T.H. Chan School of Public Health, found that the head-scratching was justified—it replicated the earlier results but then showed how a single snapshot of a person’s weight doesn’t tell the whole story.

The findings, reported today in the Annals of Internal Medicine, used data from 225,072 participants in 2 long-term studies—the Nurses’ Health Study and the Health Professionals Follow-up Study—who were followed for 16 years, in contrast with earlier work that relied on a single measurement of body mass index (BMI) taken at baseline.

This new study identifies each participant’s maximum BMI over the 16-year period, and measures all-cause mortality and cause-specific mortality. In contrast with the study that found the “obesity paradox” in those with the highest BMI levels—groups with BMI of 30 to 35 kg/m2 and those with BMI 35 kg/m2 and higher—were associated with greater risk of death for any reason.

This relationship held up for both and women and across age groups; those most at risk from carrying excess weight were younger than age 70 and had never smoked. The most overweight patients also had greater risk of death from specific causes, including cardiovascular disease and coronary heart disease.

The researchers did a separate analysis that looked at the relationship between all-cause mortality and BMI at the beginning of the study, and this result was consistent with the earlier work that found an “obesity paradox.”

Explanations for the obesity paradox included the idea that obese patients might be watched more closely by physicians or take more medication for conditions like high blood pressure or cholesterol. These new findings amplify the need to maintain a healthy weight, the researchers say.

The US Preventive Services Task Force calls for health plans to screen patients who are overweight for cardiovascular disease and to refer those with a BMI of 30 kg/m2 or higher to a behavioral intervention to help them lose weight.  

Reference

Yu E, Ley SH, Manson JE, et al. Weight history and all-cause and cause-specific mortality in three prospective cohort studies [published online April 4, 2017]. Ann Intern Med. 2017; DOI: 10.7326/M16-1390.

 
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