Bone loss occurs and osteomalacia, in adults (rickets in children), results due to Vitamin D deficiency. Impaired Calcium absorption occurs due to very low levels of the vitamin. Suggest he gets a bone density test to check the integrity of his bones. Vitamin D is available through our foods - Fortified milk, breakfast cereals, egg yolks, fatty fish, fish oils, and the sun. Sit at a window with the sun shining in for about 1/2 hour (few times a week) and that will help you get enough Vitamin D. Hope this helps you.