NTR5206 Research Assignment Paper: Vitamin D Nutrition

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African Americans have lower serum 25-hydroxyvitamin D con- centrations and a lower risk of fragility fractures than do other populations. I review the evidence on factors other than vitamin D that might explain this paradox and the calcium economy in different life stages. Researchers are actively trying to explain this genetically programmed advantage. Factors that could pro- tect African Americans against fracture include their higher peak bone mass, increased obesity rates, greater muscle mass, lower bone turnover rates, and advantageous femur geometry. In addi- tion, bone histomorphometry in young adults shows longer peri- ods of bone formation. Although African Americans fall as fre- quently as do whites, the direction of their falls and their manner of breaking falls could protect them from fractures. African American girls accrue more calcium than do white girls during adolescence as the result of increased calcium absorption and superior renal calcium conservation. In adulthood, higher para- thyroid hormone concentrations do not result in increased bone loss in African Americans because of their skeletal resistance to parathyroid hormone, and their superior renal conservation of calcium persists. These advantages diminish in the elderly, in whom further increases in parathyroid hormone result in in- creased bone turnover and bone loss. Ultimately, I explain the paradox by multiple factors associated with fracture risk and calcium economy in African Americans. Despite African Amer- icans’ reduced risk of osteoporotic fractures, such fractures re- main an important public health problem for this population that vitamin D intervention studies have not addressed. Am J Clin Nutr 2008;88(suppl):545S–50S.

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