The prevalence of hypovitaminosis D and secondary hyperparathyroidism in obese Black Americans

Context Both obesity (body mass index, BMI >= 30 kg/m(2)) and Black race are associated with a higher risk of vitamin D deficiency and secondary hyperparathyroidism. We hypothesized the risk of hypovitaminosis D would therefore be extraordinarily high in obese Black adults. Objective To study the effects of race and adiposity on 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (iPTH). Design, Setting and Participants Cross-sectional study of 379 Black and White adults from the Washington D.C. area. BMI ranged from 19(.)9 to 58(.)2 kg/m(2). Main Outcome Measures Prevalence of hypovitaminosis D [25(OH)D < 37(.)5 nmol/l] and secondary hyperparathyroidism [25(OH)D < 37(.)5 nmol/l with iPTH > 4(.)2 pmol/l]. Results Obese Black subjects had lower mean 25(OH)D, 40(.)3 (SD, 20(.)3) nmol/l, compared with obese Whites, 64(.)5 (29(.)7), P < 0(.)001, nonobese Blacks, 53(.)3 (26(.)0), P = 0(.)0025 and nonobese Whites, 78(.)0 (33(.)5), P < 0(.)001. The prevalence of hypovitaminosis D increased with increasing BMI, and was greater (P < 0(.)001) in Blacks than Whites within all BMI categories examined. Among subjects with BMI >= 35 kg/m(2), 59% of Blacks vs 18% of Whites had hypovitaminosis D (odds ratio 6(.)5, 95% confidence interval 3(.)0-14(.)2). iPTH was negatively correlated with 25(OH)D (r = -0(.)31, P < 0(.)0001), suggesting those with hypovitaminosis D had clinically important vitamin D deficiency with secondary hyperparathyroidism. For secondary hyperparathyroidism 35(.)2% of Blacks met the criteria, compared to 9(.)7% of Whites (OR 3(.)6, CI 1(.)5-98(.)8). Conclusions Obese Black Americans are at particularly high risk for vitamin D deficiency and secondary hyperparathyroidism. Physicians should consider routinely supplementing such patients with vitamin D or screening them for hypovitaminosis D.