The form of provitamin D is decreased and the active form of vitamin D is increased. This increase in vitamin D can enhance calcium absorption, but it also accelerates bone resorption. So bones turn over their cells very quickly and perhaps the calcium absorption is not quick enough to maintain bone mass. In one study, bone density was greater in treated celiacs than in untreated celiacs. However, the bone mass was still lower than in a group of non-celiacs.
Children are very resilient, however.
Children who are diagnosed and compliant have a greater annual increment of bone mass than non celiac children. Adults who were treated from childhood and are still compliant have bone mineral density equal to that of nonceliac adults. We should definitely evaluate every new celiac for bone mineral density as soon as possible, and by means of a bone densitometry exam. This is to get a baseline, so we can either treat or prevent osteoporosis. Also, to prevent bone derangements, we should encourage sound dietary compliance, evaluate for lactose intolerance, discourage excess caffeine, alcohol, and smoking.