WASHINGTON — Vitamin D levels are inadequate in up to half of postmenopausal women who receive treatment for osteoporosis, Ethel Siris, M.D., reported during an international symposium sponsored by the National Osteoporosis Foundation.
Vitamin D inadequacy was significantly worse among women who took less than 400 IU of vitamin D supplementation daily, compared with women who took at least 400 IU of vitamin D daily (63% vs. 45%).
Previous study findings suggest that serum 25-hydroxyvitamin D concentrations of at least 30 ng/mL are needed to stabilize serum parathyroid hormone levels, Dr. Siris, director of the metabolic bone diseases program at Columbia University, New York, and her colleagues, wrote in a poster presentation.
In a cross-sectional, observational study conducted between November 2003 and March 2004, the investigators collected blood samples from 1,536 postmenopausal women, mean age 71 years, at 61 sites throughout North America.
They used several cut points of serum 25-hydroxyvitamin D to define inadequacy—less than 9 ng/mL, less than 20 ng/mL, less than 25 ng/mL, and less than 30 ng/mL.
Parathyroid hormone values stabilized among patients with serum 25-hydroxyvitamin D concentrations of at least 29.8 ng/mL, which suggests that concentrations of approximately 30 ng/mL are important for healthy parathyroid levels.
Additional factors significantly related to vitamin D inadequacy in a multivariate analysis included age older than 80 years, BMI greater than 30, lack of exercise, and lack of physician counseling about the importance of vitamin D.
More than half (59%) of the women reported that they had not discussed vitamin D with a doctor.
Dr. Siris is a paid consultant for Eli Lilly & Co., Merck & Co., Sanofi Aventis, Procter and Gamble Pharmaceuticals, and Novartis.