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 post-menopausal 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.
ASJC Scopus subject areas
- Internal Medicine