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

Authors: DAWSON-HUGHES BE - TUFTS-HNRCA; HARRIS SUSAN S - TUFTS-HNRCA; KRALL ELIZABETH - TUFTS-HNRCA; DALLAL GERARD E - TUFTS-HNRCA; FALCONER GLADYS - TUFTS-HNRCA; GREEN CAROL L - TUFTS-HNRCA

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Although supplementation with vitamin D has been shown to reduce hip fracture rates in selected populations, the amount of vitamin D needed to minimize bone loss in ambulatory adults is uncertain. We recently demonstrated that in healthy postmenopausal women in Boston (latitude 42 degrees N), a total intake of 500 IU of vitamin D per day (100 from diet; 400 from supplement) is more favorable to the spine than an intake of 100 IU per day (from diet). However, there is currently no evidence that a total intake of 200 IU per day, the current recommended dietary allowance (RDA) in the U.S., is less beneficial to bone than a higher intake of vitamin D. To test the adequacy of the RDA, we recruited 247 healthy postmenopausal women who consumed an average of 100 IU of vitamin D per day and randomly assigned them to treatment with an additional 100 or 700 IU per day. Their total vitamin D intakes during the study averaged 200 IU and 800 IU per day. All women took a 500 mg calcium supplement throughout the study. Bone mineral density of the hip, spine, and whole body was measured every 6 months for 2 years. Women consuming 800 IU of vitamin D lost less bone mineral from hip than those consuming 200 IU per day. Changes in bone density at the spine and whole body were minimal over the two years. We conclude that the current RDA of 200 IU of vitamin D per day is adequate to limit bone loss from the spine and whole body but a higher vitamin D intake is needed to minimize bone loss from the hip in healthy postmenopausal women living in the temperate zone.

Technical Abstract: This study was conducted to determine whether increasing vitamin D intake above the recommended dietary allowance (RDA) of 200 IU per day reduces bone loss in healthy postmenopausal women residing at latitude 42 degrees N. In a double-blind, 2-year trial, 247 healthy postmenopausal women who consumed an average of 100 IU of vitamin D in their diets were randomized to either 100 IU or 700 IU of vitamin D per day. All women received 500 m of calcium daily as citrate malate. Duplicate hip and spine and single whole-body scans were performed by dual-energy x-ray absorptiometry at 6 month intervals selected to flank the periods when 25 hydroxyvitamin D levels are highest (summer/fall) and lowest (winter/spring). Plasma 25-hydroxyvitamin D and seru osteocalcin were measured in these seasons in year 1. Both treatment groups lost bone mineral density (BMD) from the femoral neck, but the 700 IU group lost less than the 100 IU group (-1.06+/-0.34 (SE) vs 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 years. Serum osteoclcin and plasma 25-hydroxyvitamin D (100 IU group only) fluctuated with season. In conclusion, an intake of 200 IU of vitamin D per day is sufficient to limit bone loss from the spine and whole body but a higher intake is needed to minimize bone loss from the femoral neck in healthy calcium-supplemented postmenopausal women residing at latitude 42 degrees N.