Prevalence of inadequate vitamin D intake in spinal muscular atrophy type I population as it correlates with bone health

Spinal Muscular Atrophy (SMA) is an autosomal recessive disease that causes a degeneration of the anterior horn cells of the spinal cord. SMA Type I is the most severe form, characterized by progressive muscle weakness and atrophy. SMA Type I patients are susceptible to nutritional deficiencies, especially those that correlate to bone health, due to decreased caloric intake and limited weight bearing. The aim of this study was to evaluate and assess: 1) the adequacy of vitamin D intake as compared to the American Academy of Pediatrics recommendation of 400 IU/day; 2) the correlation between vitamin D intake and associated serum level; and 3) the association between vitamin D and calcium intakes and bone mineral density. All subjects are participants in an ongoing natural history study at the University of Utah. Participants have a genetic diagnosis of SMA and a clinical diagnosis of Type I. Vitamin D and calcium intakes were assessed with a 3-day food record. Vitamin D serum levels were evaluated from 25-hydroxy vitamin D lab testing. Bone mineral density (BMD) was assessed using Dual Energy X-ray Absorptiometry Scan (DEXA) of the subjects' whole body. Subjects (n=40) consisted of 22 males and 18 females. The mean age of the subjects was 18.6 months (range 0 to 165 months). Seventy-five percent of patients had an inadequate intake of vitamin D at the initial visit. Vitamin D intake and calcium intake were positively correlated with BMD (1=0.31 and 1=0.53, respectively). Increased vitamin D and calcium consumption were associated with an increase in BMD (p=0.04 and p=0.01, respectively). Vitamin D intake correlated positively with serum levels of vitamin D (1=0.65). Within a subset of 14 patients, 71% had a serum vitamin D level in the optimal range. The majority of patients (75%) reported an inadequate vitamin D intake at their first visit (<400 IU). Inadequate nutrient intake is likely due to the decreased caloric needs of SMA Type I patients. Decreased intake of vitamin D and calcium were associated with a decreased BMD which increases the risk of fractures, scoliosis, and osteoporosis. There continues to be a need for evidence-based research concerning the nutritional needs of SMA Type I patients. Future research involving an experimental study is necessary to determine optimal intakes of vitamin D and calcium in the SMA Type I population.