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. Although the risk of osteoporotic fractures in black women is only about half the risk in white women, the risk triples in both groups between the ages of 50 and 80. Since longevity is increasing in the black population, osteoporotic fractures will become an even greater problem for this ethnic minority in the future. The elderly require higher intake of vitamin D to prevent bone loss resulting from secondary hyperparathyroidism. Calcium with sufficient vitamin D supplementation decreases 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, 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. 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 1,25 dihydroxyvitamin D levels required to overcome the hyperparathyroidism associated with aging. 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 (September, 2007) concluded that research in this population is a high priority. It is essential to learn whether elderly blacks benefit from increased vitamin D intake, since these individuals would tend to receive higher doses of vitamin D than whites to compensate for lower baseline 25(OH)D levels, exposing them to potential harm without a compensatory benefit.
Because African Americans have fewer osteoporotic fractures, they have been excluded from studies of the effect of vitamin D on prevention of osteoporosis. We propose to evaluate the effect of maintaining optimal vitamin D status on the rate of decline in bone density and physical performance in elderly black women over a four-year period. A positive response to vitamin D supplementation would demonstrate the applicability of this safe, inexpensive strategy for preventing osteoporotic fractures in this minority population.
|Aloia, John; Mikhail, Mageda; Dhaliwal, Ruban et al. (2015) Free 25(OH)D and the Vitamin D Paradox in African Americans. J Clin Endocrinol Metab 100:3356-63|
|Aloia, John; Dhaliwal, Ruban; Mikhail, Mageda et al. (2015) Free 25(OH)D and Calcium Absorption, PTH, and Markers of Bone Turnover. J Clin Endocrinol Metab 100:4140-5|