Ferritin levels and risk of metabolic syndrome: meta-analysis of observational studies

Background: Elevated ferritin levels have been associated with single cardiovascular risk factors but the relationship to the presence of metabolic syndrome is inconclusive. The aim of this systematic review and meta-analysis of published observational studies was to estimate the association between serum ferritin levels and metabolic syndrome in adults. Methods: The Pubmed, SCOPUS and the Cochrane Library databases were searched for epidemiological studies that assessed the association between ferritin levels and metabolic syndrome and were published before September 2013. There were no language restrictions. Two investigators independently selected eligible studies. Measures of association were pooled by using an inverse-variance weighted random-effects model. The heterogeneity among studies was examined using the I-2 index. Publication bias was evaluated using the funnel plot. Results: Twelve cross-sectional, one case-control and two prospective studies met our inclusion criteria including data from a total of 56,053 participants. The pooled odds ratio (OR) for the metabolic syndrome comparing the highest and lowest category of ferritin levels was 1.73 (95% Cl: 1.54, 1.95; I-2 = 75,4%). Subgroup analyses indicate that pooled OR was 1.92 (95% Cl: 1.61, 2.30; I-2 = 78%) for studies adjusting for C-reactive protein (CRP), and 1.52 (95% Cl: 1. 36, 1.69; I-2 = 41%) for studies that did not adjust for CRP (P = 0.044). This finding was remarkably robust in the sensitivity analysis. We did not find publication bias. Conclusions: The meta-analysis suggests that increased ferritin levels are independently and positively associated with the presence of the metabolic syndrome with an odds ratio higher than 1.73.