To date, research has generated a mass of data showing that insufficient vitamin intake can promote, in part, the development of chronic diseases such as cardiovascular disease, cancer and osteoporosis. In addition, clinical trials have shown that vitamins in diet, fortified foods or dietary supplements are effective in preventing deficiency-related diseases.
On the other hand, studies have indicated that vitamin intake may not translate into risk reduction of disorders depending on a multitude of lifestyle factors, of which diet is only one. Other research has associated disease risk reduction with vitamins in food but not with supplement intake. The contradictory results show the complexity of the relationship between health and nutrition (see also Principles – The contradictory science of micronutrients).
Fact is that an adequate intake of vitamins and other micronutrients is essential for virtually all chemical processes within the body and is necessary for a healthy life. But vitamins and other micronutrients in diet, fortified foods or dietary supplements cannot compensate for unhealthy lifestyle choices such as eating junk food, smoking or drinking to excess.