Excerpt from a nutrition textbook that explains the importance of vitamins for human health. It defines vitamins and classifies them as fat-soluble and water-soluble, providing detailed information on each vitamin's chemical properties, functions, dietary requirements, deficiency symptoms, toxicity risks, food sources, and stability. The chapter also discusses plant nutrients (phytochemicals), emphasizing the importance of consuming a variety of fruits and vegetables for optimal health. Finally, it explores the use of dietary supplements, offering recommendations for specific situations where supplementation may be beneficial while warning against the potential risks of megadoses.