Vitamin D in polycystic ovary syndrome: Relationship to BMI and insulin sensitivity (#119)
Background: Vitamin D is a fat soluble vitamin that has been correlated with insulin resistance (IR) . Weight loss has been shown to improve both IR and Vitamin D levels ; however relationships between adiposity, Vitamin D and IR are unclear.
Objective: To explore the relationships between Vitamin D, IR and body mass index (BMI) in women with PCOS and weight-matched controls.
Design: Cross-sectional study
Setting: Tertiary medical centre
Participants: 21 overweight and 22 lean women with PCOS and 16 overweight and 19 lean BMI-matched control women without PCOS were studied at baseline.
Method: Following recruitment from community advertisement and screening, women were withdrawn from interfering medications and studied following a 3 month washout period. Blood samples were taken for Vitamin D and metabolic markers. Detailed body composition measures and gold standard euglycaemic hyperinsulinaemic clamps were performed.
Main Outcome Measures: Plasma levels of Vitmain D and glucose infusion rate (GIR) on clamp study and adiposity measures.
Results: Vitamin D levels were lower in overweight PCOS women compared with overweight controls (31.6 and 46.1 nmol/L respectively, p=0.01). Overall correlations revealed strong correlation between GIR and BMI (r=-0.58) and moderate correlation with BMI (r=-0.34) and GIR (r=0.30). Independent regression analysis between Vitamin D and BMI revealed a beta coefficient of -0.86 (p=0.002), indicating for every 1 unit increase in BMI, Vitamin D is reduced by 0.86 nmol/L. For GIR and Vitamin D, the beta coefficient was 0.06, p=0.012.
Sub-group analysis of the overweight cohort (n=37) showed that the PCOS group had significantly lower Vitamin D levels compared to the overweight non-PCOS group (beta coefficient -14.46, p=0.01). This difference in Vitamin D levels remained significant after adjusting for BMI (beta coefficient =-13.96, p=0.01). However, when adjusted for GIR this difference in Vitamin D was no longer significant between the two groups.
Conclusions: Vitamin D levels are lower in overweight women with PCOS compared to overweight controls but were similar within the lean cohort. Overall, BMI is the key correlate of Vitamin D status and this relationship may be in part mediated by IR.
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