Compensation for the interracial variance in the cutaneous synthesis of vitamin D
Matsuoka, L.Y.; Wortsman, J.; Chen, T.C.; Holick, M.F.
Journal of Laboratory and Clinical Medicine 126(5): 452-457
1995
ISSN/ISBN: 0022-2143 PMID: 7595030 Document Number: 440930
We investigated the homeostatic compensation for the lower cutaneous synthesis of vitamin D in heavily melanized persons. Vitamin D-2 (50,000 IU) was administered in a single oral dose to 24 young adults, 12 blacks and 12 whites, matched for age, gender, and socioeconomic status. We also included a group of eight healthy elderly white adults as representatives of a population with a nonracial mechanism for decreased cutaneous vitamin D synthesis. Plasma determinations were performed under basal conditions and at 6, 10, and 24 hours after vitamin D intake. Basal 25-hydroxyvitamin D (25-OH-D) levels were significantly lower in blacks (12.5 +- 2.2 ng/ml (mean +- SEM)) and in elderly whites (19.2 +- 1.9 ng/ml), compared with young whites (30.2 +- 3.0 ng/ml (p lt 0.0001)); levels of basal 1,25-dihydroxyvitamin D (1,25(OH)-2-D) did not differ between groups. The vitamin D blood curve was similar between groups after the oral vitamin D-2 load. Increases in 25-OH-D were 91.7 +- 15.9% in blacks, 18.8 +- 5.2% in young whites, and 28.6 +- 6.9 in elderly whites; 1,25(OH)-2-D levels increased slightly and did not differ between groups, although in blacks the change over time was significant (p lt 0.05). As a whole, the study populations exhibited a strong relation between basal and peak 25-OH-D (r = -0.80; p lt 0.001). Levels of intact parathyroid hormone and serum calcium of blacks and young whites did not differ within or between groups throughout the test. We conclude that these healthy populations with varying basal 25-OH-D levels had similar vitamin D plasma responses to oral administration of vitamin D-2. Moreover, the subsequent hydroxylation of vitamin D was inversely proportional to the prevailing concentration of 25-OH-D and was similar in blacks and whites. Thus, the suppressive effect of racial pigmentation on vitamin D substrate availability is effectively compensated by intrinsic, race-independent properties of 25-hydroxylation of vitamin D.