A Harvard review published in the Journal of the American Medical Association in 2002 recommended that all adults should take a multivitamin daily. Statistics suggest that many people do not consume optimal amounts of vitamins in their diets. Low levels of vitamins can contribute to the development of a variety of conditions. Additionally, recent studies have shown that nutrient levels in fruits, vegetables, and some food crops have decreased over the past 50 years. This may be mainly due to the way food is grown, processed, and prepared.