Bone Abstracts

Background: The ‘adequate’ level of 25-hydroxyvitamin D (25OHD) in children remains unclear. For bone outcomes, parathyroid hormone (PTH) is an important functional biomarker. Prior studies have shown too weak a correlation between 25OHD and PTH levels to determine adequate 25OHD level.

Objective: To determine adequate 25OHD level(s) in children using a normal PTH value of 65 pg/ml while adjusting for calcium intake.

Design: We performed a cross-sectional study in 403 children; 237 were healthy (age 10.2±4.4 years; 51% male) and 166 were chronically ill (9.9±4.2 years; 53% male). Diseases in ill children were cancer, osteogenesis imperfecta, connective tissue disorders, and motor disabilities.

Results: Serum 25OHD <20 ng/ml was present in 41% of healthy and 66% of ill children, while 25OHD <10 ng/ml was present in 3.0% of healthy and 11.4% of ill children. PTH was negatively correlated with both 25OHD and caIcium intake (r=−0.11, P=0.02 and r=−0.25, P=0.01 respectively). The 25OHD–PTH correlation became stronger when adjusted for calcium intake: For caIcium <600 mg/day: r=−0.45 (P=0.02), 600–1500 mg/day: r=−0.30 (P<0.001) and >1500 mg/day: r=−0.27 (P<0.001). Serum 25OHD levels that maintain a PTH concentration of <65 pg/ml were: 24 ng/ml at caIcium intake <600 mg/day, 19 ng/ml at 600–1500 mg/day, and 11 ng/ml at >1500 mg/day.

Conclusions: PTH can help define adequate 25OHD levels for bone outcomes when the 25OHD–PTH correlation is adjusted for caIcium intake in children. Based on the serum 25OHD level that maintains PTH <65 pg/ml, we propose adequate 25OHD levels for three ranges of calcium intake. To improve generalizability of these findings, we encourage replication of our analysis in diverse populations.