Carotenoids, vitamin A, and their association with the metabolic syndrome: a systematic review and meta-analysis.

CONTEXT

Modifiable factors that reduce the burden of the metabolic syndrome (MetS), particularly plant-derived biomarkers, have been a recent focus of rising interest.

OBJECTIVE

This systematic review and meta-analysis, which follows PRISMA guidelines, evaluates evidence from a period of 20 years that links vitamin A and carotenoids with the occurrence of MetS and following the PRISMA guidelines.

DATA SOURCES

PubMed and Cochrane databases (January 1997 through March 2017) were systematically assessed for studies, including case-control, cross-sectional, and cohort studies, that evaluated the associations of MetS with carotenoids and retinyl esters and retinol (vitamin A).

DATA EXTRACTION

Key measures of associations were harmonized into odds ratios (ORs) and 95% confidence intervals (95%CI) of MetS per 1 standard deviation (SD) of exposure using forest plots and random effects models that pooled data points from 11 cross-sectional studies. Begg's funnel and harvest plots were constructed.

RESULTS

An inverse association between total carotenoids and MetS was found [ORpooled, 0.66; 95%CI, 0.56-0.78; 1 SD ∼ 0.82 µmol/L; n = 5 studies]. This association was the strongest for β-carotene, followed by α-carotene and β-crypotoxanthin. No association was detected between retinol and MetS (ORpooled, 1.00; 95%CI, 0.88-1.13; 1 SD ∼ 2.14 µmol/L; n = 6 studies). Publication bias was absent, and harvest plots indicated consistency upon replication for β-carotene and total carotenoid exposures.

CONCLUSIONS

This review and meta-analysis suggests that, unlike retinol, total and individual carotenoids were inversely related to MetS.