According to Ryan N. Harrison, in Vitamins: What They Are, How They Work, Why You Need Them, What We May Not Know Is Without a good multivitamin supplement, you are likely not getting the amount of vitamins your body needs to function optimally. Although many people consider their diets to be "in compliance," the truth is that it is incredibly difficult to follow a diet that meets FDA vitamin levels. (Harrison). According to the Dietary Guidelines for Americans, on the FDA website they state that: “Many people consume more calories than they need without taking the recommended amounts of a number of nutrients. The guidelines warn that there are many nutrients, including vitamins. —for whom low dietary intake may be a concern."