Normal vitamin D levels and bone mineral density among children with inborn errors of metabolism consuming medical food–based diets

A higher incidence of osteopenia is observed among children with inherited metabolic disorders (inborn errors of metabolism, or IEMs) who consume medical food–based diets that restrict natural vitamin D–containing food sources. We evaluated the vitamin D status of children with IEMs who live in the Pacific Northwest with limited sun exposure and determined whether bone mineral density (BMD) in children with phenylketonuria (PKU), the most common IEM, correlated with diet or biochemical markers of bone metabolism. We hypothesized that children with IEMs would have lower serum vitamin D concentrations than controls and that some children with PKU would have reduced bone mineralization. A retrospective record review of 88 patients with IEMs, and 445 children on unrestricted diets (controls) found the 25-hydroxyvitamin D concentrations were normal and not significantly different between groups (IEM patients, 27.1 ± 10.9; controls, 27.6 ± 11.2). Normal BMD at the hip or spine (−2 < z score < 2) was measured in 20 patients with PKU. There was a correlation between lumbar spine BMD and dietary calcium intake. We saw no evidence of low serum vitamin D in our population of children with IEMs compared with control children. We also found no evidence for reduced BMD in children with PKU on specialized diets, but BMD was associated with calcium intake. Dietary intake of essential nutrients in medical food–based diets supports normal 25-hydroxyvitamin D levels and BMD in children with IEMs, including PKU. The risk of vitamin D deficiency among patients consuming a medical food–based diet is similar to the general population.