Indexed on: 05 Apr '16Published on: 05 Apr '16Published in: Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists
To compare levels of 25-hydroxyvitamin D (25[OH]D) associated with a plateauing of intact parathyroid (iPTH) across latitudes among adults with African ancestry.This study included approximately 500 adults of African ancestry ages 25-45 years living in four sites: Chicago, IL (: 41° N), Jamaica (17° N), Ghana (6° N), and South Africa (34° S). Multivariate linear regression models, a non-linear logistic growth curve model and piecewise linear models with a single knot were fitted to estimate the 25[OH]D level associated with a plateauing of iPTH with adjustment for covariates. Goodness of fit was compared using computer intensive permutation tests.Mean age was 34.7 (SD 6.2) years and 46.5% were male. Within each site, the percentage of participants with iPTH level ≥ 65 pg/ml was higher among women vs. men and was most frequent among South African women (17.1%) and lowest among Jamaican men (0.6%). Goodness of fit tests supported linear regression as the preferred model for the association between iPTH and 25[OH]D in the four sites with no 25[OH]D level associated with iPTH plateauing in any site. The slope of the association between 25[OH]D and iPTH differed by latitude and was strongest in U.S.. (β= -0.81; 95% CI = -1.03, -0.59), and weakest in Jamaica, (β= -0.45; 95% CI -0.71, -0.18) with covariate adjustment but differences in slopes were small.The association between 25[OH]D and iPTH appears linear among adults with African ancestry regardless of latitude within a range of 25[OH]D levels between 10-60 ng/ml.