The individual actions of vitamins in the body cannot always be easily disentangled because nutrients work interdependently, or with each other. The presence or absence of one vitamin may affect another vitamin's absorption, metabolism or excretion. A deficiency of one vitamin may alter the action of another vitamin or may create a deficiency of another vitamin as well.
History
The concept of vitamins ushered in the scientific field of nutrition 100 years ago. For centuries, people suspected that a diet may relate to certain diseases, such as oranges preventing scurvy. But not until Christian Eijkman in 1906 published his theory of micronutrients did anyone know how food might prevent disease.
Then in 1912, Casimir Funk found the factor that prevents beriberi, the thiamine deficiency disease. He named this nitrogen compound, or amine, a "vital amine," or vitamin, according to Kathleen Mahan and Sylvia Escott-Stump in the text "Krause's Food, Nutrition and Diet Therapy." Understanding how vitamins work together contributes to achieving and maintaining optimal health.
Activation
Some vitamins activate other vitamins, and some pairs of vitamins activate each other. For instance, vitamin B12 and folate, another B vitamin, each depend on the other for activation. Vitamin B12 acts as a coenzyme that activates folate, and folate activates vitamin B12, according to Eleanor Whitney and Sharon Rolfes in the text "Understanding Nutrition."
Coenzyme Conversion
Riboflavin (vitamin B2) and vitamin B6 provide an example of one vitamin converting another vitamin to a different form. One of the riboflavin coenzymes assists the enzyme that converts vitamin B6 to its coenzyme form. Consequently, a severe riboflavin deficiency can impair vitamin B6 activity.
Joint Functions
Some vitamins work together to perform a vital job. For instance, the synthesis of DNA for the formation of new cells depends on both folate and vitamin B12. In another example, riboflavin, vitamin B6 and iron all work together to convert the amino acid tryptophan into niacin (vitamin B3). Consequently, an inadequate intake of either riboflavin or vitamin B6 can diminish the body's niacin supply.
Similar Activity
Some vitamins have similar activity. Carotenoids such as beta-carotene have vitamin A activity. Three different chemically related forms of vitamin A, collectively called the retinoids, include retinol, retinal and retinoic acid.
Bone-Making Team
Vitamins A, D and K work together to build and maintain bones. Vitamin D maintains blood concentrations of calcium and phosphorus. Vitamin K participates in the synthesis of bone proteins that bind to minerals. Vitamin D regulates that synthesis. Vitamin A may control the response of bone-building genes to vitamin D.
Fat-soluble vitamins also interact with minerals. For instance, vitamin D and calcium cooperate in forming bones, and zinc assists in making retinol-binding protein needed to transport vitamin A.
Antioxidants
Some vitamins protect each other from oxidation damage. For instance, vitamin E protects vitamin A from oxidation. If vitamin E is deficient, vitamin A absorption and storage are impaired.
References
- "Krause's Food, Nutrition and Diet Therapy (10th Edition)"; Mahan and Escott-Stump; 2000
- "Understanding Nutrition (Ninth Edition)"; Eleanor Noss Whitney and Sharon Rady Rolfes; 2002
- FDA: Fortify Your Knowledge About Vitamins
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