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 (Exp Clin Endocrinol Diabetes, 2006)