New Study Questions “Obesity Paradox”

A new Danish study finds overweight and obese patients were neither more or less likely to die from a stroke than normal-weight individuals, a finding that authors say supports the recommendation to strive for normal weight.

Researchers from Frederiksberg University in Denmark report that, while overweight status and obesity are associated with stroke, overweight or obese patients “do not carry a significant survival advantage” over their normal-weight counterparts. The authors also note that previous studies have observed lower mortality rates among patients with higher body-mass indexes for chronic conditions including stroke, and reports of an “obesity paradox” have led to uncertainty regarding secondary prevention in obese patients with stroke.
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They add, however, that their study suggests overweight and obese patients are not protected from stroke-associated mortality compared with their normal-weight counterparts, and that some body mass index data had to be imputed, which could potentially bias their results.

In an attempt to determine whether the aforementioned “obesity paradox” is real or an artificial finding due to selection bias, the researchers studied survival after stroke in relation to body-mass index in 71,617 patients. To overcome selection bias, they studied only deaths caused by the index stroke, on the assumption that death by stroke reported on a death certificate was due to the index stroke if death occurred within the first month post-stroke.

The investigators used the Danish Stroke Register, containing information on all hospital admissions for stroke in Denmark from 2003 to 2012, and the Danish Registry of Causes of Death. The study included all registered Danes for whom information was available on body-mass index, age, sex, civil status, stroke severity, stroke subtype, a predefined cardiovascular profile, and socioeconomic status.

Among these patients, 7878, or 11 percent, had died within the first month. Of these patients, stroke was the cause of death of 5512 (70%). Of the patients for whom information on body-mass index was available, 9.7% were underweight, 39 percent were of normal weight, 34.5% were overweight, and 16.8% were obese. Body mass index was inversely related to mean age at stroke onset. There was no difference in the risk for death by stroke in the first month among patients who were normal weight, overweight, and obese. Analysis of deaths within 1 week produced similar results.

Ultimately, the authors found no evidence of an obesity paradox in patients with stroke, with stroke occurring at a significantly younger age in patients with higher body-mass index. Thus, the researchers said, obese patients with stroke should continue to aim for normal weight.

“It appeared from our study that those who are obese experience stroke 6 years before those who are normal weight, and in the case of the overweight, stroke occurred 2 years earlier in life than in normal weight persons,” says Tom Olsen, MD, PhD, a physician in the stroke unit at Frederiksberg University, and lead researcher.

“Based on these results,” he says, “obese and overweight stroke patients should be advised to strive for normal weight.”

—Mark McGraw

Reference

Dehlendorff C, Andersen K, et al. Body Mass Index and Death by Stroke: No Obesity Paradox. JAMA Neurology. 2014.