Low serum 25-hydroxyvitamin D concentrations are associated with insulin resistance in women with polycystic ovary syndrome

S. Hahn; U. Haselhorst; S. Tan; B. Quadbeck; K. Mann; O. E. Janssen

doi:10.1055/s-2006-932856

Experimental and Clinical Endocrinology & Diabetes, Inhaltsverzeichnis

Low serum 25-hydroxyvitamin D concentrations are associated with insulin resistance in women with polycystic ovary syndrome

S Hahn ¹, U Haselhorst ², S Tan ¹, B Quadbeck ³, K Mann ¹, OE Janssen ¹

¹Div. of Endocrinology, University of Duisburg-Essen, Essen, Germany
²Biofocus, Laboratory Associates, Recklinghausen, Germany
³Haus der Medizin, Essen, Germany

Abstract

Objectives: Polycystic ovary syndrome (PCOS) is a common endocrine disorder characterised by chronic anovulation and hyperandrogenism. In addition, insulin resistance and central obesity are prevalent in PCOS women. Vitamin D is thought to play a role in the pathogenesis of type 2 diabetes by affecting insulin metabolism. The aim of our study was to investigate the effect of vitamin D on insulin resistance in PCOS.

Methods: In 118 untreated PCOS patients (median age 28 years) levels of 25-hydroxyvitamin D (25-VitD) (RIA method provided by DiaSorin), calcium and anorganic phosphate were measured. In addition, endocrine, anthropometric and metabolic variables were evaluated and a glucose tolerance test was performed to assess indices of insulin and glucose metabolism (HOMA-IR, AUC-I, Matsuda index).

Results: In the entire PCOS cohort, 25-VitD concentrations were negatively correlated with BMI (r=-0.278, p=0.0023), fasting insulin (r=-0.261, p=0.0046), HOMA-IR (r=-0.309, p=0.0007), AUC-I (r=-0.251, p=0.0073) and fasting glucose (r=-0.329, p=0.0005), and positively correlated with the Matsuda index as a parameter of insulin sensitivity (r=0.229, p=0.0179). Furthermore, 25-VitD correlated with sex-hormone-binding-globuline (r=0.303, p=0.0011) and consequently also with the free androgen index (r=-0.237, p=0.0148). Subgroup analysis of insulin resistant (HOMA-IR >2.5, n=73) and non insulin resistant PCOS women (n=45), revealed significant lower 25-VitD levels in insulin resistant patients (median 11.3, range 2.9–50.6 vs. 19.1, 4.3–59.5 ng/ml; p=0.0038). Differences remained significant when women were divided according to their 25-VitD levels. Women with hypovitaminosis D (25-VitD <9 ng/ml) had higher mean BMI levels (median 34.5, range 20–51 vs. 31.0, 19–46kg/m²) and higher HOMA-IR scores (median 4.6, range 0.7–11.2 vs. 3.0, 0.5–18.1) compared to women with 25-VitD levels in the normal range (all p<0.05). No differences were found in calcium and phosphate levels.

Conclusion: In PCOS women, low 25-VitD levels are associated with obesity and insulin resistance.