A dose-response meta-analysis of the impact of body mass index on stroke and all-cause mortality in stroke patients: a paradox within a paradox

The obesity paradox is often attributed to fat acting as a buffer to protect individuals in fragile metabolic states. If this was the case, one would predict that the reverse epidemiology would be apparent across all causes of mortality including that of the particular disease state. We performed a dose-response meta-analysis to assess the impact of body mass index (BMI) on all-cause and stroke-specific mortality among stroke patients. Data from relevant studies were identified by systematically searching PubMed, OVID and Scopus databases and were analysed using a random-effects dose-response model. Eight cohort studies on all-cause mortality (with 20,807 deaths of 95,651 stroke patients) and nine studies of mortality exclusively because of stroke (with 8,087 deaths of 28,6270 patients) were evaluated in the meta-analysis. Non-linear associations of BMI with all-cause mortality (P < 0.0001) and mortality by stroke (P = 0.05) were observed. Among overweight and obese stroke patients, the risk of all-cause mortality increased, while the risk of mortality by stroke declined, with an increase in BMI. Increasing BMI had opposite effects on all-cause mortality and stroke-specific mortality in stroke patients. Further investigations are needed to examine how mortality by stroke is influenced by a more accurate indicator of obesity than BMI.