Determine Effect of Vitamin D on Bone Health in Elderly African American Women Clinical Trial
Official title:
Vitamin D and Osteoporosis Prevention in Elderly African American Women: A 4-year Randomized, Double-blind, Placebo-controlled Study to Investigate the Effect of Vitamin D Status in Elderly African American Women
Vitamin D is a hormone that is produced when sunlight is absorbed by the skin. Vitamin D insufficiency has been recognized as a problem in areas where sun exposure is limited, especially in the wintertime. In addition, the more pigmented the skin is, the less capable it is of utilizing sunlight to make vitamin D. Vitamin D plays an important role in helping the body absorb calcium and in building strong bones. It has also been shown to improve muscle function in the elderly. As we get older, our vitamin D levels in the blood go down and this may increase the risk for falls and fractures. If we can improve vitamin D status as we age, we may be able to improve muscle strength and decrease the risk of falls and fractures.
The long-term goal of this project is to develop strategies for the prevention of
osteoporotic fractures in African Americans. Most intervention studies have excluded African
Americans because of the erroneous belief that osteoporosis is not a major health problem in
this population. In fact, the incidence rate of hip fracture in blacks is 50% of the rate in
whites. Since longevity is increasing in the black population, osteoporotic fractures will
become an even greater problem for this ethnic minority in the future. Furthermore, morbidity
and mortality from osteoporotic fractures is greater in blacks. The elderly require higher
intake of vitamin D to prevent bone loss resulting from secondary hyperparathyroidism.
Calcium with sufficient vitamin D supplementation may decrease fractures in elderly white
populations as a result of reduction in bone loss and falls (improved physical performance).
The only fracture intervention study to include African Americans—the Women's Health
Initiative—used an inadequate dose of vitamin D (400 IU), a dose unlikely to achieve the
vitamin D status proposed by U.S. experts: serum 25 hydroxyvitamin D [25(OH)D] concentration
above 75 nmol/L. No calcium/vitamin D intervention studies on fall prevention or physical
performance have included African Americans.
As a result of increased skin pigmentation, blacks synthesize less vitamin D from sun
exposure. As a result, serum 25(OH)D levels are often in the "insufficient" range. This is
accompanied by secondary hyperparathyroidism, but adult blacks have a relative skeletal
resistance to PTH, so that they have lower bone turnover. They also have more efficient renal
conservation of calcium starting in childhood. Addition of vitamin D3 to a calcium-sufficient
African American postmenopausal population does not prevent bone loss. The calcium/vitamin D
requirements of black adults may be lower than white adults through midlife. However, the
elderly require more vitamin D to produce the higher 25(OH)D levels required to overcome the
hyperparathyroidism associated with aging. The skeleton of elderly African Americans appears
to be susceptible to the increasing parathyroid hormone levels of old age. Bone loss
accelerates and bone turnover markers increase in elderly African Americans just as in
whites. The specific aims of this project are to determine if dietary supplementation with
calcium/vitamin D will safely reduce bone loss and bone turnover and improve physical
performance in elderly African Americans. We will enroll 250 African American women in a
four-year vitamin D3 intervention trial where serum 25(OH)D will be maintained at an optimum
level above 75 nmol/L. Adequate calcium intake will be ensured. Functional markers of vitamin
D including bone density, serum PTH, and bone turnover will be measured. The NIH Conference
on Vitamin D and Health in the 21st Century, September 5-6, 2007 concluded that research in
this population is a high priority.
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