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Title: An inflection point of serum 25-hydroxyvitamin D for maximal suppression of parathyroid hormone is not evident from multi-site pooled data in children and adolescents

Author
item HILL, KATHLEEN - Purdue University
item MCCABE, GEORGE - Purdue University
item MCCABE, LINDA - Purdue University
item GORDON, CATHERINE - Children'S Hospital - Boston, Massachusetts
item ABRAMS, STEVEN - Children'S Nutrition Research Center (CNRC)
item WEAVER, CONNIE - Purdue University

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2010
Publication Date: 11/1/2010
Citation: Hill, K.M., McCabe, G.P., McCabe, L.D., Gordon, C.M., Abrams, S.A., Weaver, C.M. 2010. An inflection point of serum 25-hydroxyvitamin D for maximal suppression of parathyroid hormone is not evident from multi-site pooled data in children and adolescents. Journal of Nutrition. 140(11):1983-1988.

Interpretive Summary: Vitamin D is important for bone health. In adults, when vitamin D levels in the blood are low, parathyroid hormone (PTH) levels in the blood are high and this can cause bone loss. Blood 25-hydroxyitamin D [25 (OH) D] level is a measurement of the vitamin D level in the blood. Preventing high blood PTH levels has commonly been used to determine whether there is enough 225 (OH) D in the blood. We do not know if this is true in children. Data from 735 participants, ages 7­18 y, were pooled from 3 study sites located in Indiana, Texas, and Massachusetts. We did not find a meaningful relationship between 25(OH) D and PTH in these children. This brings into question the value of using PTH to assess vitamin D status in children to determine if a child is vitamin D deficient.

Technical Abstract: In adults, maximal suppression of serum parathyroid hormone (PTH) has commonly been used to determine the sufficiency of serum 25-hydroxyvitamin D [25(OH) D]. In children and adolescents, the relationship between serum 25(OH) D and PTH is less clear, and most studies reporting a relationship are derived from relatively small samples and homogeneous cohorts. Our objective was to determine the relationship between serum 25(OH) D and PTH in children and adolescents, from a large and diverse U.S. cohort and to identify a point of inflection of serum 25(OH) D for maximal suppression of serum PTH. Data from 735 participants, ages 7–18 y, were pooled from 3 study sites located in Indiana, Texas, and Massachusetts. A two-phase linear spline was used to model the relationship between serum 25(OH) D and PTH. The value of serum 25(OH) D for maximal suppression of serum PTH was identified as the inflection point of the spline. Before adjustment for site, the inflection point of serum 25(OH) D for maximal suppression of serum PTH was 92.4 nmol/L (95% CI: 62.2, 130.7). After adjusting for site, the point of inflection was poorly defined and the relationship between serum 25(OH) D and PTH appeared to be linear. The lack of an inflection point of serum 25(OH) D for maximal suppression of PTH brings into question the value of using maximal suppression of serum PTH as a basis for determining optimal serum 25(OH) D for healthy children and adolescents.