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Vitamin D economy in blacks
Felicia Cosman1, Jeri Nieves, David Dempster
1Regional Bone Center and Clinical Research Centers, Helen Hayes Hospital, West Haverstraw, New York, USA.
Summary
Black individuals exhibit lower fracture risk and higher bone mineral density (BMD) despite lower vitamin D levels. Their skeleton shows resistance to parathyroid hormone (PTH), suggesting effective adaptations to vitamin D deficiency.
Area of Science:
- Bone Biology and Metabolism
- Nutritional Science
- Racial Disparities in Health
Background:
- Black individuals paradoxically have lower fracture risk and higher bone mineral density (BMD) than white individuals, despite lower serum 25-hydroxyvitamin D (25(OH)D) levels.
- Lower vitamin D levels in Black populations are attributed to increased skin pigmentation, leading to reduced vitamin D production.
- Black individuals exhibit higher parathyroid hormone (PTH) levels and a greater prevalence of secondary hyperparathyroidism in response to lower vitamin D and calcium intake.
Purpose of the Study:
- To investigate the physiological adaptations in Black individuals that contribute to their skeletal health despite lower vitamin D status.
- To understand the differential response of the Black skeleton to parathyroid hormone (PTH) compared to the white skeleton.
- To evaluate the efficacy of vitamin D supplementation for bone health in Black populations.
Main Methods:
- Comparison of bone mineral density (BMD), vitamin D status (25(OH)D), and parathyroid hormone (PTH) levels between Black and white individuals.
- Assessment of biochemical indices of bone turnover and bone formation rates using histomorphometry.
- Evaluation of bone resorption markers during a parathyroid hormone (PTH) infusion in both racial groups.
- Review of vitamin D supplementation studies in Black women.
Main Results:
- Black individuals have lower mean 25(OH)D levels and higher PTH levels, associated with higher 1,25(OH)(2)D and lower urinary calcium excretion.
- Biochemical indices of bone formation, including osteocalcin, are generally lower in Black individuals.
- The Black skeleton demonstrated resistance to the bone-resorbing effects of PTH, while renal sensitivity to PTH was maintained or enhanced.
- Vitamin D supplementation studies in Black women showed inconsistent benefits for BMD.
Conclusions:
- Skeletal and renal adaptations to vitamin D deficiency in Black individuals may be highly effective, potentially limiting further benefits of vitamin D supplementation for bone health.
- The Black skeleton's resistance to PTH's bone-resorbing effects is a key factor in maintaining skeletal integrity despite lower vitamin D levels.
- While vitamin D supplementation may not significantly benefit bone health in Black individuals, it may play a role in preventing other chronic diseases.
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The solar UV B rays (290-315 nm) are absorbed by the skin, and 7-dehydrocholesterol (provitamin D3) photolyzes it to previtamin D3, which undergoes a rapid transformation to vitamin D3(cholecalciferol).
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