Vitamins, minerals and amino acinds are essential for normal cell function in the human body, from maintainig healthy tissue and bone and brain function to metablism and central nervous system; a definiency can cause health problems, from heart disease to cancer. Those who eat a balanced diet containing enough vegetable, fruit and grains don't risk vitamin deficiency, and evidence suggest they do not benefit from taking vitamins. 

But vitamins and mineral supplements have become a popular consumption worldwide, especially among those who see their diet anything but balanced. Against this increasing use, there are also emerging scientific opinions that question the extent to which these supplements can prevent chronic diseases or extend life, while others contend that it would take long-term, controlled trials to prove or disprove their benefits.