The effect of body mass index on stroke prognosis: A systematic review and meta-analysis of 32 cohort studies with 330,353 patients

Background: Many studies have explored the impact of body mass index (BMI) on stroke prognosis, yet findings remain inconsistent. Aims: The aims of this study were to conduct a systematic review and meta-analyses to summarize the existing evidence on BMI and stroke outcomes. Methods: PubMed, Web of Science, Embase, The Cochrane Library, CNKI, CBM, Wanfang Database, and VIP Database were systematically searched from inception to 1 January 2023. Cohort studies were included if they reported on a population of patients with stroke, evaluated BMI on stroke outcomes (mortality/recurrence/score of modified Rankin scale (mRs)), and reported original data. Data extraction and quality assessment were independently undertaken by two reviewers. Stata 16.0 software was used for meta-analysis. Results: Thirty-two studies involving 330,353 patients (5 Chinese language articles) were included in the analysis. The proportion of underweight, overweight, and obese patients was 1.85%, 18.2%, and 15.6%, respectively. Compared with normal weight, being underweight was associated with an increased risk of mortality (relative risk (RR) = 1.78, 95% confidence interval (CI) = 1.60–1.96), poor functional outcomes defined as modified Rankin scale ⩾ 3 (RR = 1.33, 95% CI = 1.22–1.45), and stroke recurrence (RR = 1.19, 95% CI = 1.04–1.37). Being overweight but not obese was associated with reduced mortality (RR = 0.81, 95% CI = 0.74–0.89) and better functional outcomes (RR = 0.92, 95% CI = 0.89–0.96), but did not alter the risk of stroke recurrence (RR = 1.03, 95% CI = 0.90–1.17). Obesity was associated with lower risk of mortality (RR = 0.76, 95% CI = 0.72–0.81) and better functional outcomes (RR = 0.89, 95% CI = 0.84–0.94). Conclusions: Our findings indicate that in patients with stroke, being underweight is associated with an increased risk of mortality, poor functional outcomes, and stroke recurrence. In contrast, being overweight but not obese, or being obese, was associated with a decreased risk of mortality and better functional outcomes. This is consistent with the obesity paradox in stroke, whereby obesity increases stroke risk in the general population but is associated with improved outcome in patients suffering stroke.