Vitamins are micronutrients, or substances that the body uses in small amounts, as compared to macronutrients, which are the proteins, fats, and carbohydrates that make up all food. Vitamins are present in food, but adequate quantities of vitamins may be reduced when food is overcooked, processed, or improperly stored. For instance, processing whole wheat grain into white flour reduces the contents of vitamins B and E, fiber, and minerals, including zinc and iron. The body requires vitamins to support its basic biochemical functions, and deficiencies over time can lead to illness and disease.

^ Dwyer, J. T; Wiemer, K. L; Dary, O; Keen, C. L; King, J. C; Miller, K. B; Philbert, M. A; Tarasuk, V; Taylor, C. L; Gaine, P. C; Jarvis, A. B; Bailey, R. L (2015). "Fortification and Health: Challenges and Opportunities". Advances in Nutrition: An International Review Journal. 6 (1): 124–131. doi:10.3945/an.114.007443. PMC 4288271. PMID 25593151.

For instance, foods rich in vitamin E and beta-carotene are healthy and can help reduce cancer risk. However, the U.S. Preventive Services Task Force (USPSTF) and the American Academy of Family Physicians (AAFP) recommend against taking vitamin E or beta-carotene for the prevention of cardiovascular disease. People who smoke or are at risk for lung cancer also should avoid beta-carotene. It can increase their risk of lung cancer.

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