Parathyroid hormone-vitamin D dynamics vary according to the definition of vitamin D deficiency in newborn infants.

Abstract

Parathyroid hormone (PTH) is an indirect functional indicator of vitamin D status. Risk of vitamin D deficiency, assessed using circulating 25-hydroxyvitamin D (25(OH)D), is defined as <30nmol/L by the National Academy of Medicine and alternatively <25nmol/L in the global consensus recommendation on prevention and management of nutritional rickets. To test PTH concentrations and the odds for elevated values according to vitamin D deficiency cut-points (<30nmol/L, or <25nmol/L) in newborn infants. Healthy term-born infants (n=858) were recruited from Montreal, Canada (2016-2019). Obstetric data were obtained from medical records, and demographic factors surveyed. Immunoassays were used to measure newborn (24-36h) serum PTH and 25(OH)D; 25(OH)D was standardized to National Institute of Standards and Technology (NIST) standard reference materials. Serum PTH was log-transformed before comparing serum 25(OH)D groups (<30 vs. ≥30; or <25 vs. ≥25nmol/L) using ANCOVA adjusted for infant sex, type of delivery, parity, race, and family income. The odds of elevated PTH (>71.48pg/mL) were tested using logistic regression, adjusted for the same covariates. Infants (50.2% female) were 39.6±1.0weeks gestational age (mean±SD), and 3.41±0.38kg. Median serum 25(OH)D was 45.4 (IQR 23.2) nmol/L; 20.5% had serum 25(OH)D<30nmol/L, and 12.4% <25nmol/L. Median serum PTH was 30.72 (IQR 33.90) pg/mL, elevated in 12.7% overall, and higher in infants born with serum 25(OH)D<25 vs. ≥25nmol/L (35.96 (IQR 39.20) vs. 30.36 (IQR 32.93) pg/mL, p=0.0158). The odds of elevated PTH were higher when serum 25(OH)D was <25nmol/L (ORadj 2.13, 95% CI: 1.23, 3.69). PTH concentration and the odds of being elevated did not differ according to the 30nmol/L cut-point. Based on this study, the definition of vitamin D deficiency relative to bone health as set by the National Academy of Medicine (<30nmol/L) exceeds the threshold at which PTH is elevated in newborn infants.