Serum vitamin D and its association with acute ischemic stroke severity: A systematic review

Objectives: Vitamin D deficiency is common in acute ischemic stroke (AIS) and has been proposed as a potential prognostic factor. However, evidence regarding its association with stroke severity and outcomes remains inconsistent. This review evaluated the association between serum vitamin D levels and neurological severity, functional outcome, and infarct volume in AIS. Materials and Methods: PubMed, Scopus, and Web of Science were searched for observational studies assessing serum vitamin D in relation to stroke severity measured by the National Institutes of Health Stroke Scale (NIHSS), functional outcome using the modified Rankin Scale (mRS), and infarct volume. Meta-analyses of correlation coefficients were performed. Subgroup analyses were conducted according to stroke onset, geographic region, and vitamin D assay method. Results: Eighteen studies met the inclusion criteria, of which 14 (2,242 participants) contributed to the primary meta-analysis. Serum vitamin D levels were moderately and inversely correlated with NIHSS scores at admission (r = −0.39, 95% confidence interval [CI] −0.45 to −0.32; I 2 = 65%). Lower vitamin D levels were also associated with worse functional outcomes on the mRS (6 studies, 538 participants; r = −0.43, 95% CI −0.60 to −0.27; I 2 = 83%) and with larger infarct volumes on magnetic resonance imaging (4 studies, 710 participants; r = −0.29, 95% CI −0.41 to −0.16; I 2 = 73%). Subgroup analyses showed consistent inverse associations across stroke onset, geographic region, and assay methods, although substantial heterogeneity remained. Conclusion: Lower serum vitamin D levels are associated with greater neurological severity, poorer functional outcomes, and larger infarct volumes in AIS. However, substantial heterogeneity limits causal inference.