Vitamin D status, trunk muscle strength, body sway, falls, and fractures among 237 postmenopausal women with osteoporosis - Pfeifer, M; Begerow, B; Minne, H W; Schlotthauer, T; Pospeschill, M; Scholz, M; Lazarescu, A D; Pollähne, W (Experimental and Clinical Endocrinology & Diabetes, 2001)