RATES OF BONE LOSS IN POSTMENOPAUSAL WOMEN RANDOMLY ASSIGNED TO ONE OF 2 DOSAGES OF VITAMIN-D

We conducted a study to determine whether increasing vitamin D intake above the recommended dietary allowance (RDA) of 5.0 mu g (200 IU)/d r educes bone loss in healthy postmenopausal women residing at latitude 42 degrees N. In this double-blind, randomized 2-y trial, we enrolled 247 healthy ambulatory postmenopausal women who consumed an average of 2.5 mu g (100 IU) vitamin D/d in their usual diets. The women were gi ven either 2.5 mu g (100 IU) or 17.5 mu g (700 IU) vitamin D/d. Ah wom en received 500 mg supplemental calcium per day as citrate malate. Dup licate hip and spine and single whole-body scans were performed by dua l-energy x-ray absorptiometry at 6-mo intervals selected to flank the periods when 25-hydroxycholecalciferol (calcidiol) concentrations are highest (summer/fall) and lowest (winter/spring). Plasma calcidiol and serum osteocalcin were measured in these seasons in year 1. Both trea tment groups lost bone mineral density from the femoral neck, but the 17.5-mu g group lost less than (-1.06 +/- 0.34%; ($) over bar x +/- SE ) the 2.5-mu g group (-2.54 +/- 0.37%, P = 0.003). Seventy percent of the benefit each year occurred in winter/spring and 30% in summer/fall . Changes in spinal and whole-body bone densities did not differ by tr eatment group and were minimal after 2 y. Serum osteocalcin and plasma calcidiol (2.5-mu g group only) fluctuated with season. In conclusion , in healthy, calcium-supplemented, postmenopausal women residing at l atitude 42 degrees N, an intake of 5.0 mu g (200 IU) vitamin D/d is su fficient to limit bone loss from the spine and whole body but it is no t adequate to minimize bone loss from the femoral neck. We recommend t hat postmenopausal women at this latitude increase their vitamin D int ake above the current RDA of 5.0 mu g/d to reduce bone loss from the h ip. Although an intake as high as 20 mu g (800 IU)/d may not be needed , this amount is safe and effective.