Bone Abstracts

Objectives: Nutritional rickets results from the interaction of poor vitamin D status and limited calcium intake. Vitamin D requirements are greater in children with limited intake of calcium. We sought to determine the serum 25-hydroxyvitamin D [25(OH)D] concentration that can prevent rickets in calcium-deprived Nigerian children.

Methods: We reanalyzed data from a case-control study of Nigerian children with active rickets (cases) and age-, sex-, and weight-matched control subjects without rickets in an area where dietary calcium insufficiency is common (J Pediatr 2000;137:367-73). Active clinical rickets was confirmed radiographically, and serum 25(OH)D was measured by immunoassay. We performed a multivariate logistic regression to assess the odds of rickets associated with varying 25(OH)D values, while adjusting for calcium intake and other risk factors.

Results: A total of 118 children with rickets and 117 control children had sufficient data (n=235) for multivariate analysis. Rachitic children had a mean (±SD) age of 51.3±24.3 months, and 53 (45%) were male. Cases and controls had similarly low mean dietary calcium intakes (216±89 and 209±92 mg/day, respectively). In a model adjusted for weight for height and calcium intake, the odds ratio (95% confidence interval) for rickets was 13.8 (4.1–47) for 25(OH)D <30 nmol/L, 4.3 (1.6–11.6) for 30–39 nmol/L, 0.8 (0.3–2.5) for 40–44 nmol/L, and 0.13 (0.04–0.43) for ≥50 nmol/L, compared with the range of 45–49 nmol/L. In an unadjusted model, the area under the receiver operating characteristic (ROC) curve was 0.84, indicating a strong relationship of 25(OH)D with having rickets. In the fully adjusted model, the area under the ROC curve was 0.89.

Conclusion: In Nigerian children with a low dietary calcium intake of approximately 200 mg/day, a 25(OH)D concentration below 40 nmol/L was associated with nutritional rickets. These results emphasize the utility of the multivariable modeling approach in the study of 25(OH)D and calcium requirements to prevent rickets. In future studies, standardized 25(OH)D measurements, dietary calcium intake, life-style data, and a consistently applied case definition of ‘rickets’ are needed to move the field forward.

Disclosure: The authors declared no competing interests.