Serial ultraviolet B exposure and serum 25 hydroxyvitamin D response in young adult American blacks and whites: no racial differences.

We tested the hypothesis that repeated whole body suberythemal ultraviolet B (UVB) exposure would result in less increase of serum 25-hydroxyvitamin D (25OHD) concentrations in black compared with white young adults with no significant change or racial differences in serum calciotropic hormones concentrations. Thirteen white and 7 black adults ranging from 22 to 35 years of age were submitted to sequential total body suberythemal doses of UVB (280-315 nm) biweekly for 6 weeks. Initial UVB dose was 5% below the minimal erythemal dose for the most sensitive skin, followed by 10% increase per exposure for 4 weeks. Blood samples were drawn weekly. Baseline 25OHD concentrations were significantly lower in blacks compared to whites, but the increases in serum 25OHD concentrations were similar in both groups; there were no significant differences by sex or age. Serum 24,25-dihydroxyvitamin D [24,25-(OH)2D] concentrations paralleled the serum 250HD response. Mean serum calcium (total and ionized), magnesium, phosphate, alkaline phosphatase, vitamin D binding protein, C-terminal parathyroid hormone, calcitonin, 1,25-dihydroxyvitamin D [1,25-(OH)2D], and osteocalcin concentrations did not differ between blacks and whites at any time. The ratio of the concentration of 1,25-(OH)2D to 25OHD in their serum was initially higher in blacks compared to whites (p less than 0.0001); the ratios decreased to levels similar to whites by the third UVB exposure. We conclude that, in blacks and whites, sequential suberythemal UVB exposure produces similar elevations of serum 25OHD concentrations and unchanged calciotropic hormones concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)