Rates of bone loss in postmenopausal women randomly assigned to one of two dosages of vitamin D.

We conducted a study to determine whether increasing vitamin D intake above the recommended dietary allowance (RDA) of 5.0 micrograms (200 IU)/d reduces 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 micrograms (100 IU) vitamin D/d in their usual diets. The women were given either 2.5 micrograms (100 IU) or 17.5 micrograms (700 IU) vitamin D/d. All women received 500 mg supplemental calcium per day as citrate malate. Duplicate hip and spine and single whole-body scans were performed by dual-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 treatment groups lost bone mineral density from the femoral neck, but the 17.5-micrograms group lost less than (-1.06 +/- 0.34%; mean +/- SE) the 2.5-micrograms 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 treatment group and were minimal after 2 y. Serum osteocalcin and plasma calcidiol (2.5-micrograms group only) fluctuated with season. In conclusion, in healthy, calcium-supplemented, postmenopausal women residing at latitude 42 degrees N, an intake of 5.0 micrograms (200 IU) vitamin D/d is sufficient to limit bone loss from the spine and whole body but it is not adequate to minimize bone loss from the femoral neck.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women.

OBJECTIVES: To determine whether relative vitamin D deficiency during the winter months contributes to age-related bone loss and whether rates of change in hard- and soft-tissue mass vary during the year. DESIGN: Double-blind, placebo-controlled, 1-year trial in 249 women in which equal numbers of women were randomized to either placebo or 400 IU of vitamin D daily. All women received 377 mg/d of supplemental calcium largely as calcium citrate malate. PATIENTS: Healthy, ambulatory postmenopausal women with usual intakes of vitamin D of 100 IU/d. MEASUREMENTS: Duplicate spine and whole-body scans were done by dual energy x-ray absorptiometry at 6-month intervals that were timed to periods when 25-hydroxyvitamin D levels were highest and lowest. Period 1 was June-July to December-January and period 2 was December-January to the next June-July. Serum parathyroid hormone and plasma 25-hydroxyvitamin D levels were measured during periods 1 and 2. MAIN RESULTS: In the placebo group, spinal bone mineral density increased in period 1, decreased in period 2, and sustained no net change. Women treated with vitamin D had a similar spinal increase in period 1 (1.46% compared with 1.40% in placebo), less loss in period 2 (-0.54% compared with -1.22%, CI for the difference, 0.05% to 1.31%, P = 0.032) and a significant overall benefit (0.85% compared with 0.15%, CI for the difference, 0.03% to 1.37%, P = 0.04). In period 2, 25-hydroxyvitamin D levels were lower and parathyroid hormone levels were higher in the placebo than in the vitamin D group. Whole-body lean and fat tissue and bone mineral density varied during the year but did not change overall. CONCLUSIONS: At latitude 42 degrees, healthy postmenopausal women with vitamin D intakes of 100 IU daily can significantly reduce late wintertime bone loss and improve net bone density of the spine over one year by increasing their intake of vitamin D to 500 IU daily. A long-term benefit of preventing vitamin D insufficiency in the winter seems likely although it remains to be shown. Observed changes in bone as well as in fat and lean tissue appear to be related to season.