The Relationship Between Parathyroid Hormone and 25-Hydroxyvitamin D During and After Pregnancy

Caroline K. Kramer, Chang Ye, Anthony J. Hanley, Philip W. Connelly, Mathew Sermer, Bernard Zinman, Ravi Retnakaran
2016 Journal of Clinical Endocrinology and Metabolism  
Context: There is debate about whether women may need greater vitamin D supplementation when pregnant. However, it is unclear whether the 25-hydroxyvitamin D (25-OH-D) concentration required for suppression of PTH (ie, suggesting vitamin D sufficiency) differs between pregnancy and the nongravid state. Objective: To systematically characterize the relationship between 25-OH-D and PTH during and after pregnancy. Design/Setting/Participants: In this study, 468 women underwent serial assessment of
more » ... serum 25-OH-D and PTH in late pregnancy, at 3 months postpartum, and at 12 months postpartum. At each visit, segmented regression analysis was performed to: 1) determine the best model to fit the relationship between 25-OH-D and PTH; and 2) identify the 25-OH-D threshold above which PTH is maximally suppressed. Results: Serum 25-OH-D and PTH were inversely correlated at each of the pregnancy (r ϭ Ϫ0.33; P Ͻ .0001), 3 months postpartum (r ϭ Ϫ0.37; P Ͻ .0001), and 12 months postpartum (r ϭ Ϫ0.34; P Ͻ .0001) assessments. In pregnancy, PTH first rises when 25-OH-D falls below 82 nmol/L (95% confidence interval, 61-103) and follows a linear relationship with declining 25-OH-D thereafter. In contrast, at both postpartum visits, there was a curvilinear relationship between 25-OH-D and PTH below the 25-OH-D threshold at which PTH is suppressed (71 nmol/L [61-81] at 3 months and 81 nmol/L [61-100] at 12 months). The 25-OH-D thresholds for PTH suppression in pregnancy and at 3 and 12 months postpartum were not significantly different from one another (all pairwise P Ն .26). Conclusion: Although the shape of the relationship between 25-OH-D and PTH differs between pregnancy and the postpartum, the 25-OH-D thresholds for PTH suppression are similar, supporting comparable targets for vitamin D supplementation. (J Clin Endocrinol Metab Abbreviations: BMI, body mass index; CI, confidence interval; MSE, mean squared error; 25-OH-D, 25-hydroxyvitamin D.
doi:10.1210/jc.2015-4060 pmid:26895390 fatcat:nxueubrabnhlxi4cmkjnmc7epq