The vitamin requirement of the human body is usually met by adequate nutrition. In northern countries like Finland, however, insufficient intake of vitamin D is common. Risk groups for vitamin deficiencies include small children, immigrants, people on a vegan diet, elderly with inadequate food intake, alcoholics, and patients suffering from severe systemic diseases. In these groups the prophylactic use of vitamins may be beneficial, and diagnosed vitamin deficiencies should be actively treated. Consider vitamin deficiency as a possible cause of vague or non-specific symptoms (such as aches, loss of strength, rashes) in the risk groups.Determination of the vitamin D concentration is recommended for special groups (particularly for patients with osteoporosis). From the point of view of bone health the target level of serum vitamin 25-OH-D concentration is 75-100 nmol/l.