Increased risk of Blount disease in obese children and adolescents with vitamin D deficiency.

BACKGROUND: Poor dietary habits and decreased outdoor activity has led to an epidemic of obese children and vitamin D deficiency. The lack of vitamin D alters bone development and mineralization by diminishing physiological levels of calcium and phosphorus. Given vitamin D's role in bone and growth plate mineralization and regulation, we hypothesized that vitamin D deficiency would lead to higher rates of fractures, slipped capital femoral epiphysis (SCFE), and Blount disease in obese youth.

METHODS: A retrospective review was performed at the obesity clinic using the obesity database (890 patients). Data obtained included body mass index (BMI), vitamin D levels (25-vitamin D), history of fractures, Blount disease, and/or SCFE. The chart review identified 2 populations of obese patients, those with vitamin D deficiency, <16 ng/mL (198 patients) and those not vitamin D deficient >16 ng/mL (692 patients). Fisher exact, χ², and 2-sample t tests along with logistic regression were used for statistical analysis. A P value ≤0.05 was considered statistically significant.

RESULTS: Blount disease was found to have a statistically significant (P<0.05) positive association with patient's sex, BMI, and vitamin D level. Specifically, males were 8.16 times more likely than females to be observed with Blount disease (P=0.01). Patients with very low vitamin D levels were 7.33 times more likely to have Blount disease than patients with higher levels (P=0.002). Each whole number increase in BMI increases the likelihood of Blount disease by 3% (P=0.01). There was no association between increased number of fractures or SCFE with vitamin D deficiency in these obese patients.

CONCLUSION: As our findings indicate, BMI and vitamin D levels have a strong association with Blount disease, which may be especially important among males. Ours is the first study to show a relationship between vitamin D deficiency and Blount disease, but further prospective studies are needed with larger numbers to confirm this independent association of vitamin D deficiency with Blount disease.

LEVEL OF EVIDENCE: Level III retrospective study.