Vitamin D Economy in Blacks

Abstract

ABSTRACT:The fact that fracture risk is lower and BMD is higher in blacks compared with whites is surprising in light of what is known about vitamin D status in blacks. Mean 25(OH)D levels are lower in blacks than whites at all stages of life, and a greater proportion of blacks meet criteria for vitamin D deficiency. The racial difference in serum 25(OH)D level is primarily caused by increased pigmentation reducing vitamin D production in the skin. In response to lower 25(OH)D levels and lower average calcium intake, blacks have higher average PTH levels and a higher prevalence of secondary hyperparathyroidism (twice the prevalence compared with whites for both sexes). This is associated with higher average levels of 1,25(OH) 2 D and lower urinary calcium excretion but not higher biochemical indices of bone turnover. In fact, in general, biochemical indices of bone formation (particularly osteocalcin levels) are lower in blacks. Bone formation rates assessed histomorphometrically are also lower, although wall thickness is maintained. During a 24-h PTH infusion, increments in levels of three different bone resorption markers are significantly lower in blacks than in whites, providing direct confirmation of the thesis that the black skeleton is resistant to the bone-resorbing effects of PTH, whereas renal sensitivity to PTH is maintained or perhaps even enhanced. Vitamin D supplementation studies in black women have shown inconsistent benefits to BMD. Skeletal and renal adaptations to vitamin D deficiency in blacks might be so effective that vitamin D supplementation might not confer any further benefit to the black skeleton. Benefits of vitamin D supplements in blacks may still play a role, however, in the prevention of other chronic diseases.

Vitamin D deficiency in HIV-infected patients: a systematic review

“…As expected, those variables acknowledged as risk factors for hypovitaminosis D in the general population, 61,64,66 have also been identified in HIVinfected patients. Weaker evidence was available for HIVrelated risk factors.…”

“…The three matched case-control analyses 27 a significantly higher prevalence in healthy controls in another, 30 and a significantly higher prevalence in HIV-infected patients in the third. 34 The study with the higher prevalence in the control group was performed in African-American subjects, 30 who are usually regarded as being at high risk of hypovitaminosis D. 61 As a result, both cases and controls had a very high rate of hypovitaminosis D. Paul et al 34 found a 20% greater prevalence of 25OHD ,20 ng/mL in HIV-infected patients, but they enrolled a very small sample (70 cases and 35 controls).…”

Low 25(OH) vitamin D concentrations in international UK track and field athletes

“…29 Skin colour is well recognised as a predictor of vitamin D status with numerous studies identifying lower levels in individuals with dark skin. [29][30][31] This is primarily due to increased melanin content reducing UVB absorption and subsequent vitamin D production. 32 It has also been reported that seasonal 40 This is supported by our study, which found that season was not an independent predictor and prevalence of deficiency and insufficiency were similar in the darkskinned group throughout the year, presumably because of persisting reduction in cutaneous production.…”

“…25 It has been widely recognised that mean 25(OH)D levels are lower in dark-skinned individuals at all ages, with greater risk of insufficiency and deficiency. [29][30][31] This racial difference is primarily due to increased melanin pigmentation which reduces UVB absorption and subsequent vitamin D production. 32 However, with recent public health campaigns emphasising the dangers of sunlight exposure and advocating intensive sun-block cream use, reports have also found high insufficiency rates, of around 60%, in the UK Caucasian population, and those with the fairest skin type to be, in fact, most deficient.…”

Human skin pigmentation, migration and disease susceptibility

“…The potential for pre-vitamin D 3 production is reduced further still by dark skin pigmentation. Other things being equal, the higher the eumelanin content, the lower the rate of previtamin D 3 production in the skin [2,20,21,[27][28][29][30][31][32][33][34][35][36][37][38]. When the zones of cutaneous pre-vitamin D 3 production potential are mapped following a previously established protocol [2], it is evident that lightly pigmented people inhabiting the zone near the equator can experience enough UVB through casual sun exposure on unprotected skin to produce physiologically adequate amounts of vitamin D. In the subtropical zone, there is at least one month during which there is insufficient UVB to catalyse pre-vitamin D 3 production for people with lightly pigmented skin, and during which they must rely on stored vitamin D (as 25-hydroxyvitamin D; 25(OH)D) to satisfy their physiological needs.…”