Obesity paradox: Extra weight offers better survival after a stroke

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Despite the fact that obesity increases both the risk for stroke and death, a study has found that people who are overweight or even mildly obese have better 10-year survival  after ischaemic strokes compared to those with a normal body weight.

The findings add to the ‘obesity paradox’ seen in previous studies where increased body weight appears to have a protective effect on certain groups of patients.

A stroke occurs when blood flow to an area of the brain is cut off and brain cells are deprived of oxygen and begin to die. Each year about 185,000 people die from a stroke, the fifth leading cause of death in the US and a leading cause of adult disability.

A group of participants from the Framingham Heart Study (FHS) were followed over time, including measuring their body mass index (BMI) prior to their stroke. The researchers then matched these stroke cases to other FHS participants of similar age, sex and BMI category (normal weight, overweight or obese). They then separately analysed both groups to see if overweight or obesity had any effect on survival over 10 years, compared to the people who were normal weight. “We found that participants who were overweight or mildly obese had better survival after stroke than normal weight participants and the survival benefit was strongest in males or in those younger than age 70,” explained corresponding author Dr Hugo J Aparicio, assistant professor of neurology at Boston University School of Medicine and FHS investigator.

According to the researcher, while the study controlled for factors such as smoking, cancer, dementia and ‘vascular risk factors’ like high blood pressure, diabetes and cholesterol, there may still be unhealthy aspects associated with a normal weight, like relative frailty, differences in nutrient intake or unidentified conditions that could lead to worse mortality.

The researchers caution that these results do not show that obesity is protective in the overall population. They stress that there may be some mechanism by which increased weight can help survival after stroke, whether from having the extra ‘metabolic reserve’ following a severe disease, or other influences such as medication use, avoidance of smoking or some aspect of their diet. “Nonetheless, observing this so-called ‘obesity paradox’ has important clinical implications and it is essential for clinicians and researchers to better understand the role of body weight in recovery after stroke so that they can make proper recommendations on weight loss or weight maintenance,” said Aparicio.

Abstract
Background: We investigated how body weight affects survival after stroke, leveraging the availability of multiple prestroke body mass index (BMI) measurements and using a nested case‐control design in a community‐based sample.
Methods and Results: We compared all‐cause mortality in participants stratified by prestroke weight. Separate analyses were performed for ischemic stroke and all stroke and for age‐, sex‐, and BMI category‐matched stroke‐free controls. Participants were grouped into BMI categories and followed for up to 10 years. Differences in survival were tested for interaction by case status. In sensitivity analysis, to exclude those with prestroke weight loss, we restricted the reference group to participants with 2 consistently normal BMI measurements within 10 years before stroke/matching. There were 782 stroke cases (age 71±9, 51% female participants, 87% ischemic stroke) and 2346 controls (age 72±9, 51% female participants). Overweight participants with ischemic stroke had a lower mortality compared with those with normal weight (hazard ratio [HR]=0.70, 95%CI 0.55‐0.90, P=0.005). The association of reduced mortality with BMI ≥25, compared with normal‐weight BMI 18.5 to <25, was pronounced among ischemic stroke cases but diminished with inclusion of hemorrhagic strokes (case‐control interaction P=0.051 and P=0.130, respectively). Compared with participants with stable normal weight, moderately increased weight was protective after ischemic stroke (overweight HR=0.72, 95%CI 0.53‐0.99, P=0.041).
Conclusions: Overweight and mildly obese participants had better 10‐year survival after ischemic stroke compared with normal‐weight participants, even after excluding persons with recent prestroke weight loss. There may be unknown protective factors associated with a moderately increased body weight before stroke.

Authors
Hugo J Aparicio, Jayandra J Himali, Alexa S Beiser, Kendra L Davis‐Plourde, Ramachandran S Vasan, Carlos S Kase, Philip A Wolf, Sudha Seshadri

Boston University Medical Centre material
Journal of the American Heart Association abstract


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