Association of vitamin A and its organic compounds with stroke - a systematic review and meta-analysis

The main purpose of this systematic review was to evaluate the association between the stroke (risk of stroke and the mortality due to stroke) and vitamin A, its organic compounds and its provitamins.

Major databases including PubMed, Scopus, and Web of Science were searched. Studies with human samples were included for risk assessment. The association was assessed using odds ratio (log(OR)) and a random-effect model. I statistic, variance (tau) and prediction interval were used for heterogeneity assessment. The funnel plot was used for publication bias.

Twenty-one studies including 5789 stroke patients were retrieved. Twenty studies had sufficient information for quantitative analyses. The pooled effect showed an inverse association between vitamin A and its organic compound with the risk of stroke (log(OR) = -0.46 95%CI (-0.81;-0.12)) and with the risk of mortality due to stroke (log(OR) = -0.39 95%CI (-0.74;-0.04)). However, according to subgroup analyses, the association was dependent on the compound in a way that retinol and beta-carotene were the most effective compounds. The effects of several confounding factors and the threshold levels for vitamin A and its organic compound on the effectiveness were discussed.

Insufficiency of retinol and beta-carotene significantly increased the risk of stroke; however, due to heterogeneity between studies more studies are needed for evaluating clinical significance of this outcome.