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Three-Phase Model Harmonizes Estimates of the Maximal Suppression of Parathyroid Hormone by 25-Hydroxyvitamin D in Persons 65 Years of Age and Older
Journal of Nutrition
  • Ramon A. Durazo-Arvizu, Loyola University Chicago
  • Bess Dawson-Hughes, Tufts University
  • Christopher T. Sempos, National Institutes of Health
  • Elizabeth A. Yetley, National Institutes of Health
  • Anne C. Looker, Centers for Disease Control and Prevention
  • Guichan Cao, Loyola University Chicago
  • Susan S. Harris, Tufts University
  • Vicki L. Burt, Centers for Disease Control and Prevention
  • Alicia L. Carriquiry, Iowa State University
  • Mary Frances Picciano, National Institutes of Health
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The concentration or threshold of 25-hydroxyvitamin D [25(OH)D] needed to maximally suppress intact serum parathyroid hormone (iPTH) has been suggested as a measure of optimal vitamin D status. Depending upon the definition of maximal suppression of iPTH and the 2-phase regression approach used, 2 distinct clusters for a single 25(OH)D threshold have been reported: 16-20 ng/mL (40-50 nmol/L) and 30-32 ng/mL (75-80 nmol/L). To rationalize the apparently disparate published results, we compared thresholds from several regression models including a 3-phase one to estimate simultaneously 2 thresholds before and after adjusting for possible confounding for age, BMI, glomerular filtration rate, dietary calcium, and season (April-September vs. October-March) within a single data set, i.e. data from the Tufts University Sites Testing Osteoporosis Prevention/Intervention Treatment study, consisting of 181 men and 206 women (total n = 387) ages 65-87 y. Plasma 25(OH)D and serum iPTH concentrations were (mean ± SD) 22.1 ± 7.44 ng/mL (55.25 ± 18.6 nmol/L) and 36.6 ± 16.03 pg/mL (3.88 ± 1.7 pmol/L), respectively. The 3-phase model identified 2 thresholds of 12 ng/mL (30 nmol/L) and 28 ng/mL (70 nmol/L); similar results were found from the 2-phase models evaluated, i.e. 13-20 and 27-30 ng/mL (32.5-50 and 67.5-75 nmol/L) and with previous results. Adjusting for confounding did not change the results substantially. Accordingly, the 3-phase model appears to be superior to the 2-phase approach, because it simultaneously estimates the 2 threshold clusters found from the 2-phase approaches along with estimating confidence limits. If replicated, it may be of both clinical and public health importance.

This article is from Journal of Nutrition 140 (2010): 595, doi: 10.3945/jn.109.116681.

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Ramon A. Durazo-Arvizu, Bess Dawson-Hughes, Christopher T. Sempos, Elizabeth A. Yetley, et al.. "Three-Phase Model Harmonizes Estimates of the Maximal Suppression of Parathyroid Hormone by 25-Hydroxyvitamin D in Persons 65 Years of Age and Older" Journal of Nutrition Vol. 140 Iss. 3 (2010) p. 595 - 599
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