Biological Effects of Various Regimes of 25-hydroxyvitamin D3 (calcidiol) Administration on Bone Mineral Metabolism in Postmenopausal Women

Introduction. It is evident from several studies that vitamin D inadequacy is widespread among women with osteoporosis across all continents regardless of season or latitude, with similar prevalence in patients treated for osteoporosis and in untreated women. These results underscore a need to improve physician and patient awareness of the importance of adequate vitamin D supplementation in postmenopausal women with osteoporosis.Materials and Methods. As the daily administration of vitamin D combined with 1 gr calcium is hampered by an insufficient patient adherence, we performed a longitudinal study in 90 randomly recruited postmenopausal women aged 65-75 years with inadequate calcium intake and circulating levels of 25-hydroxyvitamin D3 (lower than 30 ng/mL). The prevalence of secondary hyperparathyroidism (parathyroid hormone > 65 pg/mL) was 36% in the all population. The possible repercussion of oral single weekly or monthly calcidiol administration on phospho-calcium metabolism was observed after three months treatment (from April through July) with 500 mg calcium daily and with three different therapeutic regimens of calcidiol (Group I: 25 drops weekly; Group II: 50 drops monthly; and Group III: 100 drops monthly). The general baseline characteristics of the three groups were superimposable. We measured fasting morning serum 25-hydroxyvitamin D3, parathyroid hormone, calcium, phosphate, bone alkaline phosphatase, urinary deoxypyridinoline, and 24hr-calcium, - phosphate, and - creatinine.Results. The adherence to the weekly calcidiol treatment was over 80% in 90% of the patients. All three therapeutic regimens of calcidiol led to normalization of 25-hydroxyvitamin D3 after 3 months, yet with a significantly higher potency (P >0.01) of regimens I and III, when compared to Group II. Also the decrease of circulating levels of parathyroid hormone was significantly higher (P < 0.001) in Groups I and III versus Group II. No biochemically and clinically relevant adverse effects were observed at the end of the 90-day follow-up.ConclusionsIn postmenopausal women with inadequate circulating levels of 25-hydroxyvitamin D3, calcium and pulsed calcidiol supplementation normalized 25-hydroxyvitamin D3 levels and reduced circulating parathyroid hormone levels.