Vitamin D supplements boost the effectiveness of a popular osteoporosis drug in women with secondary hyperparathyroidism (HPTH), according to the results of an Italian study.
In a randomized, controlled trial, one group of patients was given 70 mg alendronate (Fosamax) once a week plus 0.5 µg calcitriol (Rocaltrol) daily, while another was given the weekly alendronate alone. After one year, both groups showed markedly improved bone mineral density (BMD) of the lumbar spine, femoral neck, and total hip. Patients who received the daily calcitriol, however, did considerably better. Their lumbar spine BMD increased by 6.8%, as compared with 3.7% for those who took just alendronate.
All 91 women in the study were older than 60, had a baseline bone-density score below -2.5 in at least the spine, femoral neck, or total hip, and had HPTH.
The high levels of serum parathyroid hormone (PTH) that characterize HPTH are associated with low levels of vitamin D and seem to interfere with alendronate. Patients who took the drug alone showed no significant change in PTH levels (-3.7%), but PTH plunged 32.1% among the women who added the calcitriol. And those with normalized PTH, regardless of their therapy, showed a larger increase in lumbar spine BMD than those with persistent HPTH (6.5% vs. 3.7%).
Osteoporosis is often accompanied by HPTH and vitamin deficiency, researchers note. “The role of PTH levels in BMD response to alendronate suggests the need to measure PTH in elderly patients at high risk for secondary HPTH before starting therapy, so as to implement strategies aimed at normalizing it,” they conclude (J Am Geriatr Soc. 2007;55:752-757).