Stroke survival rates in obese and overweight patients may not be as paradoxical as earlier studies indicate. Researchers in Denmark suggested in a study published June 2 in JAMA Neurology that it might be a combination of comorbid conditions, severity and selection bias.

The relationship between stroke survival and patients’ body mass index (BMI) has been under debate, as several studies have had outcomes that appeared to contradict the convention that overweight and obese individuals should strive for a normal weight to improve their health and health outcomes. Prior studies have shown better outcomes for stroke patients who were overweight or obese than their normal or underweight counterparts, called the “obesity paradox.”

The study found no correlation with the so-called “obesity paradox” and stroke survival. What researchers did find was that overweight individuals were having strokes three years earlier and obese individuals six years earlier than their normal-weight counterparts.

The Danish study looked at 71,617 patients entered into the Danish Stroke Register from March 1 2001 to Dec. 1, 2011 and followed them through the Danish Central Person Registry. If they died over the course of the study, cause of death was obtained from the Danish Registry of Causes of Death, looking only for those whose cause of death was listed as stroke within the first month after the index stroke.

While BMI was unavailable for 17,805 patents, the research team was able to make some inferences based on the data available. Beyond an increased risk for earlier stroke in overweight and obese patients, the researchers noted an increased risk of stroke and death from stroke in underweight patients, too. They hypothesized this was due to frailty.

The severity and risk of death by stroke in the normal, overweight and obese patients remained largely the same. Patients missing BMI data had more severe strokes and a higher prevalence of hemorrhagic stroke and other risk factors and therefore higher death rates.

Lead investigator Christian Dehlendorff, MS, PhD, of the Danish Cancer Society Research Center in Copenhagen, and colleagues suggested that selection bias due to failure to adjust for stroke severity may be at play in noting higher survival rates in obese patients. “In the present study, we included only patients who died of stroke within the first week and month and adjusted for stroke severity on admission, thereby adjusting for the severity of the disease that led to death,” they wrote.

As they found a higher risk of earlier strokes in overweight and obese patients, however, Dehlendorff et al cautioned patients on the upper end of the BMI scale to work toward a more normal BMI to reduce the risks and avoid progression to a disease state.