Discordant responses of bone formation and absorption markers in Japanese infants with vitamin D deficiency: a comprehensive matched case–control study

Vitamin D deficiency during infancy has been associated with increased bone turnover rate and bone mineral loss. However, few studies have examined bone turnover markers (BTMs) for both bone formation and resorption in infants with vitamin D deficiency. Here, we analyzed serum concentrations of 25(OH)D, intact parathormone (iPTH), and BTMs including total alkaline phosphatase (ALP), tartrate-resistant acid phosphatase isoform 5b (TRACP-5b), and serum type I collagen N-telopeptide (NTx) as well as basic clinical characteristics of 456 infants (626 samples) aged less than 12 months born at Saitama City Hospital, Japan (latitude 35.9° North) between January 2021 and December 2022. 116 infants (147 samples) were classified as having vitamin D deficiency (25(OH)D < 12.0 ng/mL), and 340 infants (479 samples) had sufficient vitamin D levels (25(OH)D ≥ 12.0 ng/mL). In addition to 25(OH)D and ALP, both TRACP-5b and sNTx were measured in 331 infants (418 samples), while 90 infants (105 samples) had only TRACP-5b only measured and 101 infants (103 samples) had only sNTx measured. Statistical comparison of 104 subjects each in the vitamin D deficiency and sufficiency groups after matching for the background characteristics revealed that the vitamin D deficiency group had significantly higher levels of ALP and iPTH compared with the sufficiency group (p = <0.0001, 0.0012, respectively). However, no significant differences were found in TRACP-5b and NTx levels between the two groups (p = 0.19, 0.08, respectively). Our findings suggest discordant responses between bone formation and resorption markers in subclinical vitamin D deficiency during infancy.