Disturbed metabolism of bone tissue in young children characterized by delayed bone formation and deficiency of vitamin D and calcium, the latter resulting from inadequate diet or reduced calcium absorption from the intestines. Vitamin D is important in calcium absorption and calcification of bones. It is formed in the skin from cholesterol substances under the effect of sunlight, and the deficiency is either dietary or caused by lack of sunlight. The condition was formerly prevalent in the West through lack of sun; now vitamin D is added to margarines and cooking oils, which has reduced the frequency of the condition. In developing countries it still occurs through lack of dietary calcium and fats, from which the vitamin can be formed. Characteristic signs are malformed bones, lumps on the cartilagenous outer ends of bones and delayed growth, bow legs or knock knees, and deformities of the spinal column (kyphosis, scoliosis). A related disorder is osteomalacia, caused by inadequate calcium utilization and absorption in adults. Most forms of osteomalacia and rickets react well to high doses of vitamin D and calcium, but existing deformities cannot be reversed in this way.