No obesity paradox found between BMI, stroke, and death

1. Contrary to conclusions suggested by several previous studies, the authors found no evidence of the obesity paradox (lower mortality in obese patients) in patients with stroke.

2. Patients with a higher body mass index (BMI) were more likely to have a stroke at a younger age.

Evidence Rating Level: 2 (Good)

Study Rundown: Obesity is rapidly becoming an epidemic in several societies.  While obesity is one of the causes implicated in several chronic diseases, paradoxically several studies seem to also find a pattern of lower mortality in obese patients, as compared to normal or underweight patients, when affected by these chronic conditions.  This phenomenon known as the obesity paradox is not well understood and may be an artificial finding due to selection bias.

This study examined the obesity paradox by analyzing survival rate in patients after stroke in relation to body mass index.  Utilizing data from the Danish Stroke register, the researchers studied only deaths caused by stroke by including only those reported as such on death certificates and only if death occurred within the first month after stroke.  This reduced selection bias.  The study found no relation between BMI and death after having a stroke.  It did, however, find that patients who were obese were more likely to have a stroke at a younger age.  Strengths of the study include the large population size studied and the adjustment for selection bias as detailed above.

Click to read the study, published today in JAMA Neurology

Relevant Reading: Association between obesity and mortality after acute first-ever stroke: the obesity-stroke paradox

In-Depth [retrospective cohort]: The authors of this study used data from the Danish Stroke Register that contains information on all stroke admissions in Denmark.  Patients with transient ischemic attacks and subarachnoid hemorrhages were excluded from the study.  Survival data was obtained through the Danish Central Person Registry.  Only deaths that occurred within the first month after the index stroke were included to reduce selection bias.

76,617 patients were identified from the registry.  The mean age of these patients was 71.8 years.  7878 of these patients had died within the first month, and 5512 of these patients were identified as having died due to stroke.  Adjustments were made for age, sex, stroke severity according to the Scandinavian Stroke Score, stroke subtype, civil status, cardiovascular risk factors, duration of education, and income. After adjustments, the researchers found no difference in mortality risk within the first month after a stroke among normal weight, overweight, and obese patients.  However, underweight patients did appear to have a significantly increased risk of death after a stroke (HR: 1.16; 95% CI, 1.06-1.26).

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