Although there is general agreement on the optimal calcium intake recommended for reducing postmenopausal bone loss, and it is recognized that vitamin D is important in calcium maintenance, the optimal intake of vitamin D is controversial, according to background information in the article. Blood levels of 25-hydroxyvitamin D (25-OHD) are the best indicator of vitamin D status, with very low levels leading to rickets and osteomalacia (softening of bones). Black women have lower blood levels of 25-OHD because they synthesize less through skin exposure to the sun.
John F. Aloia, M.D., from Winthrop University Hospital, Mineola, N.Y., and colleagues, conducted a randomized, double-blind trial comparing bone loss in postmenopausal black women taking vitamin D3 supplements and those not taking supplements. Two-hundred-eight healthy black women, aged 50 to 75 years, received either placebo or 20 ìg/day (micrograms per day) of vitamin D3. All participants received calcium supplements to ensure a total calcium intake of 1,200 to 1,500 mg/day. After two years, the vitamin D3 dose was raised to 50 ìg/day. Bone mineral density (BMD) was measured at six-month intervals for three years.
The researchers found that there was no significant difference in BMD in women receiving vitamin D and women receiving placebo. There was also no relationship found between 25-OHD blood levels and bone density change in either group. Both groups experienced an increase in BMD in total body, hip, and mid-radius (forearm bone) at one year (between 1.1 and 1.3 percent). However, BMD declined at these sites over the full three years from 0.26 percent to 0.55 percent. Initial total hip BMD ranged from normal (65 percent) to osteopenic (having reduced bone mass; 33.6 percent) to osteoporotic (severely reduced bone mass, 1.4 percent).
"Our study demonstrated a lack of benefit of vitamin D supplementation on loss of skeletal mass in calcium-sufficient African American women in midlife," the researchers report. "Although this may not be extrapolated to women of other ethnic groups, to elderly women, or to greater degrees of vitamin D insufficiency, it lends support to re-examination of optimal vitamin D nutrition for skeletal health in postmenopausal women of other ethnic groups."
(Arch Intern Med. 2005; 165: 1618 - 1623. Available pre-embargo to the media at www.jamamedia.org.)
Editor's Note: This research was funded by the National Institute of Aging, National Institutes of Health, Bethesda, Md.
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