Bone Abstracts

Objectives: We have previously described biochemical evidence of resistance to PTH in Indian toddlers, which reversed on calcium supplementation. We performed a post-hoc analysis on data from an RCT of vitamin D and calcium supplementation, which was designed to assess if supplementation would reduce infection rate in undernourished school children with adequate sun exposure. Specifically we investigated the effect of oral vitamin D and calcium supplementation on biochemical parameters viz serum intact PTH, calcium, phosphorous and alkaline phosphatase (ALK-P) in children with habitually low calcium intakes.

Methods: A randomized, double-blind, placebo-controlled trial was conducted on 465 children (6–12 years) from Western India (18°N). The trial included 179 children: 79 received vitamin D-calcium (1000IU-500mg) supplementation, 99 received placebo daily for 6 months. Anthropometric, dietary data and blood samples were collected at baseline, six months (end of supplementation) and 1 year post-supplementation.

Results: All anthropometric data at all three time points were below mean for age. Mean dietary calcium to phosphorus ratio was 0.4:1. Baseline mean serum 25OHD concentration was 58.2±10.9 nmol/l with no significant difference between the two groups. At 6 months, 25OHD concentration improved significantly (P<0.05) in supplemented group (83.9±30.1 nmol/l vs 58.3±15.7 nmol/l in placebo group). However, supplemented group also had significantly (P<0.05) higher PTH levels compared to non-supplemented group (6.7±3.6 pmol/l vs 5.5±3.2 pmol/l); positive correlation between serum 25OHD and PTH was noted (vs negative correlation in non-supplemented group). At 6 months mean levels of serum bone profile parameters were as follows: calcium (2.2±0.1 mmol/l), phosphorus (1.7±0.2 mmol/l) and ALK-P (178.7±40.7 IU/l). Neither at 6 months nor at 1 year post-supplementation was there significant difference between the groups in serum calcium, phosphorus and alkaline phosphatase levels. A year post-supplementation, PTH concentrations continued to remain high (but not significantly different from levels at six months); with low normal serum calcium, high normal phosphate and normal ALK-P in supplemented group.

Conclusion: In nutritionally-deprived but vitamin D sufficient children, vitamin D and calcium supplementation paradoxically increased serum PTH concentration with no apparent effect on other bone biochemistry. The mechanism for this phenomenon is unknown. However, we speculate that chronic low dietary calcium to phosphorus ratio might be responsible for this paradoxical response.

Disclosure: The authors declared no competing interests.