Low Serum 25-Hydroxyvitamin D Concentrations are Associated with Insulin Resistance and Obesity in Women with Polycystic Ovary Syndrome - Hahn, S; Haselhorst, U; Tan, S; Quadbeck, B; Schmidt, M; Roesler, S; Kimmig, R; Mann, K; Janssen, O E (Experimental and Clinical Endocrinology & Diabetes, 2006)