Dietary ß-carotene and vitamin A and risk of Parkinson disease: A protocol for systematic review and meta-analysis.

BACKGROUND: The beneficial effects of dietary ß-carotene and vitamin A on Parkinson disease (PD) have been confirmed, but some studies have yielded questionable results. Therefore, this meta-analysis investigated the effect of dietary ß-carotene and vitamin A on the risk of PD. METHODS: The following databases were searched for relevant paper: PubMed, Embase, Medline, Scopus, Cochrane Library, CNKI, Wanfang Med online, and Weipu databases for the relevant paper from 1990 to March 28, 2022. The studies included were as follows: ß-carotene and vitamin A intake was measured using scientifically recognized approaches, such as food frequency questionnaire (FFQ); evaluation of odds ratios using OR, RR, or HR; ß-carotene and vitamin A intake for three or more quantitative categories; and PD diagnosed by a neurologist or hospital records. RESULTS: This study included 11 studies (four cohort studies, six case-control studies, and one cross-sectional study). The high ß-carotene intake was associated with a significantly lower chance of developing PD than low ß-carotene intake (pooled OR = 0.83, 95%CI = 0.74-0.94). Whereas the risk of advancement of PD was not significantly distinctive among the highest and lowest vitamin A intake (pooled OR = 1.08, 95%CI = 0.91-1.29). CONCLUSIONS: Dietary ß-carotene intake may have a protective effect against PD, whereas dietary vitamin A does not appear to have the same effect. More relevant studies are needed to include into meta-analysis in the further, as the recall bias and selection bias in retrospective and cross-sectional studies cause misclassifications in the assessment of nutrient intake.