Vitamin D deficiency is pandemic in industrialized countries due to life-style changes. Recent studies suggest that besides bone-metabolism, vitamin D plays a central role in basic cell function like multiplication, differentiation and metabolism. This may explain that low vitamin D levels represent a risk factor for several apparently different diseases such as infective, autoimmune, neurodegenerative and cardiovascular diseases, as well as diabetes, osteoporosis and cancer. Accumulating evidences suggest that an adequate intake of vitamin D may significantly decrease prevalence and clinical outcome of these diseases. Estimated reduction of the economic burden might reach about 10 percent through normalizing vitamin D levels for these diseases. However, high doses of vitamin D monotherapy needs precaution for potential adverse effects and it should be substituted with the recommended doses of vitamin D in combination with synergistic vitamin A and omega 3 fatty acids, such as cod liver oil.