Vitamin D Supplementation for Adults With Neurofibromatosis Type 1 (NF1)

Individuals with NF1 and vitamin D insufficiency will be supplemented with 2 different doses of cholecalciferol (vitamin D) to see if their loss of bone mineral density is lessened over time. It is important to study vitamins as carefully as one would study medications, even though vitamins are generally safer than medications. For this reason, a carefully controlled trial of two doses of vitamin D will be performed over a 2-year period. It will include controlled doses and safety checks for participants' health to be sure that the vitamin D supplementation is safe for people with NF1. Two different doses of cholecalciferol, either 600 IU or 4,000 IU (IU means "International Units" a standard measure of the strength of the dose), will be used for supplementation. The trial is "double blind". This means that neither participant nor investigator team know which dose an individual participant might be randomized to receive until after the trial ends. In an emergency, however, the investigator can find out. Participants will be randomized to one or the other dose, and each participant will be provided a bottle of liquid called "D-drops" with a dropper that automatically drops out a measured amount when the bottle is turned upside down. Both doses of vitamin D, 600 IU and 4,000 IU, have been approved in the general population; however, it is possible that the bodies of people with NF1 handle vitamin D differently. Therefore, safety measures are assessed during this trial. Any new medical issues or concerns throughout the 2-year period will need to be recorded and assessed with the study team. The primary measure of this study is bone mineral density obtained by bone densitometry (DXA) using low-dose xrays. Bone mineral density will be tested at the beginning and the end of the trial focusing on density of bones in the hip and spine. Secondary measures of this trial include questionnaires that measure quality of life and history of bone fractures. When someone is insufficient in serum vitamin D and supplementation is recommended, it is also supplemented with calcium. Therefore, participants will be given a calcium supplement of 400 mg elemental calcium per day. A diary to keep daily track of vitamin D and calcium supplementation and documentation of fractures, should they occur, is provided.