Caroline K Kramer1, Chang Ye1, Anthony J Hanley1, Philip W Connelly1, Mathew Sermer1, Bernard Zinman1, Ravi Retnakaran1. 1. Leadership Sinai Centre for Diabetes (C.K.K., C.Y., A.J.H., B.Z., R.R.), Mount Sinai Hospital, Toronto, ON M5T 3L9, Canada; Division of Endocrinology (C.K.K., A.J.H., P.W.C., B.Z., R.R.), and Department of Nutritional Sciences (A.J.H.), University of Toronto, Toronto, ON M5S 1A1, Canada; Keenan Research Centre for Biomedical Science of St Michael's Hospital (P.W.C.), Toronto, ON M5B 1W8, Canada; Department of Laboratory Medicine and Pathobiology (P.W.C.), and Division of Obstetrics and Gynecology (M.S.), University of Toronto, Toronto, ON M5S 1A1, Canada; and Lunenfeld-Tanenbaum Research Institute (B.Z., R.R.), Mount Sinai Hospital, Toronto, ON M5T 3L9, Canada.
Abstract
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 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 = −0.33; P < .0001), 3 months postpartum (r = −0.37; P < .0001), and 12 months postpartum (r = −0.34; P < .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 ≥ .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.
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 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 = −0.33; P < .0001), 3 months postpartum (r = −0.37; P < .0001), and 12 months postpartum (r = −0.34; P < .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 ≥ .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.
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