Both low and high body iron stores relate to metabolic syndrome in postmenopausal women: Findings from the VIKING Health Study-Shetland (VIKING I)

Background: There are conflicting results among studies on the association between serum ferritin (SF) and metabolic syndrome (MetS), and by groups of sex/menopausal status. To date, there are no studies on British populations. The SF-MetS association might be U/J-shaped. We evaluated whether SF was independently associated with MetS (harmonized definition) in people from Shetland, Scotland.

Methods: We analysed cross-sectional data from the Viking Health Study-Shetland (589 premenopausal women [PreMW], 625 postmenopausal women [PostW] and 832 men). Logistic regressions using two approaches, one with the lowest sex and menopausal status-specific ferritin quartile (Q) as the reference and other using the middle two quartiles combined (2-3) as the reference, were conducted to estimate the SF-MetS association. The shape of the association was verified via cubic spline analyses. The associations were adjusted for age, inflammatory and hepatic injury markers, alcohol intake, smoking and BMI.

Results: Prevalence of MetS was 18.3%. Among PostMW both low and high SF were associated with MetS (fully adjusted odds ratios [95% confidence interval] compared to the middle two quartiles combined were: 1.99 [1.17-3.38] p =.011 for Q1 and 2.10 [1.27-3.49] p =.004 for Q4) This U-shaped pattern was confirmed in the cubic spline analysis in PostMW with a ferritin range of 15-200 ug/L. In men, a positive association between ferritin quartiles with Q1 as the reference, did not remain significant after adjustment for BMI.

Conclusion: Extreme quartiles of iron status were positively associated with MetS in PostMW, while no SF-MetS associations were found in men or PreMW. The ferritin-MetS association pattern differs between populations and U/J-shaped associations may exist.