Vitamin D biomarkers for Dietary Reference Intake development in children: a systematic review and meta-analysis

Background Circulating 25-hydroxyvitamin D [25(OH)D] has been the accepted vitamin D exposure/intake biomarker of choice within recent DRI exercises, but use of other vitamin D-related biomarkers as well as functional markers has been suggested. These may be of value in future vitamin D DRI exercises, such as the FAO/WHO's one for young children. Objectives To systematically review the usefulness of circulating 25(OH)D, parathyroid hormone (PTH), free and bioavailable 25(OH)D, C3-epimer of 25(OH)D, vitamin D-3, 24,25-dihydroxyvitamin D [24,25(OH)(2)D], and bone turnover markers and calcium absorption as vitamin D biomarkers for DRI development in children. Methods Methods included structured searches of published articles, full-text reviews, data extraction, quality assessment, meta-analysis, and random-effects meta-regression. Results Fifty-nine vitamin D supplementation randomized controlled trials (RCTs) were included (39 in infants/children as the priority group and the remainder in adults since pediatric studies were absent/limited). Vitamin D supplementation significantly raised circulating 25(OH)D in infants and children, but the response was highly heterogeneous [weighted mean difference (WMD): 27.7 nmol/L; 95% CI: 22.9, 32.5; 27 RCTs; I-2 = 93%]. Meta-regression suggested an increase by 1.7 nmol/L (95% CI: 0.7, 2.6) in serum 25(OH)D per each 100-IU increment in vitamin D intake (P = 0.0005). Vitamin D supplementation had a significant effect on circulating 24,25(OH)(2)D (WMD: 3.4 nmol/L; 95% CI: 2.4, 4.5; 13 RCTs; I-2 = 95%), with a dose-response relation (+0.15 nmol/L per 100 IU; 95% CI: -0.01, 0.29). With circulating PTH, although there was a significant effect of vitamin D on WMD (P = 0.05), there was no significant dose-response relation (P = 0.32). Pediatric data were too limited in relation to the usefulness of the other biomarkers. Conclusions Circulating 25(OH)D may be a useful biomarker of vitamin D exposure/intake for DRI development in infants and children. Circulating 24,25(OH)(2)D also showed some promise, but further data are needed, especially in infants and children.

Automated summary

This study systematically reviewed the usefulness of different biomarkers for assessing vitamin D intake/exposure in children. The results suggest that circulating 25(OH)D may be a valuable biomarker for evaluating vitamin D intake/exposure in infants and children, and circulating 24,25(OH)(2)D also shows some promise.