- Background: In a preliminary cross-sectional study of 282 OI patients we observed an inverse relationship between serum 25-hydroxyvitamin D and parathyroid hormone levels and a positive relationship between circulating levels of 25-hydroxyvitamin D and lumbar spine areal bone mineral density z-scores. This suggested that high-dose vitamin D supplementation would have a beneficial effect on bone density. Most OI patients currently receive oral vitamin D supplementation of 400 International Units per day, but doses of 2000 International Units per day are safe and have been shown to be beneficial in studies on healthy adolescents.