Slightly overweight stroke survivors have a lower risk of sustaining disabilities. The Kobe University finding adds another aspect to the obesity paradox but also highlights the importance of considering the population’s normal when recommending best practices.

The obesity paradox is the well documented observation that amongst people who suffered a stroke, those who are moderately overweight have lower rates of mortality, recurrence and readmission compared to patients of “normal” weight. Recently, survival rates have improved and attention has shifted to the subsequent lives of the patients. The Kobe University health scientist IZAWA Kazuhiro says: “In my clinical practice I have experienced that patients with a thin physique often have difficulties in recovering function whereas relatively overweight people usually fare better. This motivated me to study whether there is a demonstrable relationship between body size and functional disability after a stroke.”

Using a Japanese national database containing anonymized data on diagnosis-procedure combinations for all vascular and cardiac disease cases in hospitals across Japan, Izawa, postdoctoral researcher KANEJIMA Yuji and their team evaluated the size of different factors on over half a million patients’ disability at the time of discharge from hospital. The factors they looked at were the body mass index (BMI), which is a person’s weight relative to their height, the patients’ age, gender, their disability score at the time of hospitalization, and others.

In the journal Topics in Stroke Rehabilitation, the Kobe University team now published their results. They found that, indeed, the risk of being discharged from hospital with a poor disability score was observed to be relatively low in people with a BMI between 22.1 and 27.5 kg/m², and was lowest at a BMI of 24.7 kg/m². Given that the WHO classifies Asians with a BMI between 23 and 25 kg/m² as overweight and above that as obese, a slightly higher-than-normal BMI seems to be beneficial to the odds of recovering from a stroke with less disability. First author Kanejima offers an explanation: “The median age in this study was 77 and people in this age group and beyond lose weight more easily. However, people having certain reserves may be better able to withstand the nutritional challenge a stroke and the following hospitalization pose, which effectively protects their nervous system.”

A similar study conducted in the United States a few years ago found the same basic effect, but with an optimal BMI of 30.0 kg/m² for that population. “Asians tent to have a slimmer physique compared to Americans and this is also reflected in the lower optimal BMI for a lower probability of disability at discharge,” says Kanejima. This underscores that caution is needed when adapting BMI-based recommendations for different populations around the world.

There is concrete advice gleaned for current health care practice from the results of the present study. Izawa says: “For the public, this serves as a reminder that losing weight at a high age is a disadvantage. For health care providers, the study suggests that they need to closely monitor weight loss during hospitalization to prevent functional impairment.” To understand more about the mechanism at work, the Kobe University researchers next aim to study how the change in body weight during hospitalization is related to functional disability.

This research was funded by the Japanese Circulation Society and the Japan Society for the Promotion of Science (grants JP22K11392 and JP22K19708). It was conducted in collaboration with researchers from the National Cerebral and Cardiovascular Center.

Kobe University is a national university with roots dating back to the Kobe Commercial School founded in 1902. It is now one of Japan’s leading comprehensive research universities with nearly 16,000 students and nearly 1,700 faculty in 10 faculties and schools and 15 graduate schools. Combining the social and natural sciences to cultivate leaders with an interdisciplinary perspective, Kobe University creates knowledge and fosters innovation to address society’s challenges.