Abstract
Pathophysiological changes in vitamin D metabolism lead to hypovitaminosis (osteomalacia) and/or osteoporosis with old age and require a corresponding differential therapy. For patients with hypovitaminosis, i.e. patients with low 25-hydroxyvitamin D3 levels, a treatment with 400-800 I.E. vitamin D per day is the first choice. Subclinical or clinical osteomalacia can also be involved in the development of senile osteoporoses in patients who are more than 80 years of age, particularly in old people's homes. In principle, a distinction between hypovitaminosis and osteoporoses is necessary. There is no evidence that a treatment with low doses of vitamin D contributes significantly to a decrease in the fracture rate of patients suffering from osteoporosis who have normal substrate 25-hydroxyvitamin D levels. However, nearly all large preventive studies on osteoporosis using active vitamin D derivates revealed a significant decrease in the fracture rate while showing a rather low toxicity. The incidence of hypercalcaemia is