Abstract
An undersupply of 25-(OH) vitamin D3 (calcifediol) exists in many countries with moderate sunlight, long winters and only moderate fish consumption. Risk groups for vitamin D3 deficiency are older persons over 65 years, geriatric persons in nursing homes, infants and children/adolescents. Therefore, there are also many situations in Germany which justify vitamin D substitution; however, vitamin D3 is currently praised as a "magic bullet" against everything. But what do the data look like? Where can it help and where can it not help?