2.1.4. Vitamins

healthy-fruits-and-vegetablesA vitamin is an organic compound required by an organism as a vital nutrient in limited amounts. An organic chemical compound (or related set of compounds) is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and on the particular organism. For example, ascorbic acid (vitamin C) is a vitamin for humans, but not for most other animals, and biotin and vitamin Dare required in the human diet only in certain circumstances.

By convention, the term vitamin includes neither other essential nutrients, such as dietary minerals, essential fatty acids, or essential amino acids(which are needed in larger amounts than vitamins) nor the large number of other nutrients that promote health but are otherwise required less often. Thirteen vitamins are universally recognized at present.

Vitamins are classified by their biological and chemical activity, not their structure. Thus, each “vitamin” refers to a number of vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals is grouped under an alphabetized vitamin “generic descriptor” title, such as “vitamin A”, which includes the compounds retinal, retinol, and four known carotenoids. Vitamers by definition are convertible to the active form of the vitamin in the body, and are sometimes inter-convertible to one another, as well.

Vitamins have diverse biochemical functions:

  • Hormone-like functions as regulators of mineral metabolism (such as vitamin D)
  • Regulators of cell and tissue growth and differentiation (such as some forms of vitamin A).
  • Antioxidants (e.g.,vitamin E and sometimes vitamin C).
  • Precursors for enzyme cofactors (such as B complex vitamins) that help enzymes in their work as catalysts in metabolism. In this role, vitamins may be tightly bound to enzymes as part of prosthetic groups: For example, biotin is part of enzymes involved in making fatty acids.

Vitamins may also be less tightly bound to enzyme catalysts as coenzymes, detachable molecules that function to carry chemical groups or electrons between molecules. For example, folic acid carries various forms of carbon group – methyl, formyl, and methylene – in the cell. Although these roles in assisting enzyme-substrate reactions are vitamins’ best-known function, the other vitamin functions are equally important.

Vitamin generic
descriptor name

Deficiency disease Overdose disease Food sources

Vitamin B1

Beriberi,Wernicke-Korsakoff syndrome Drowsiness or muscle relaxation with large doses. Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs

Vitamin B12

Megaloblastic anemia Acne-like rash [causality is not conclusively established]. Meat and other animal products

Vitamin B2

Ariboflavinosis   Dairy products, bananas, popcorn, green beans, asparagus

Vitamin B3

Pellagra Liver damage (doses > 2g/day) and other problems Meat, fish, eggs, many vegetables, mushrooms, tree nuts

Vitamin B5

Paresthesia Diarrhea; possibly nausea and heartburn. Meat, broccoli, avocados

Vitamin B6

Anemia peripheral neuropathy. Impairment of proprioception, nerve damage (doses > 100 mg/day) Meat, vegetables, tree nuts, bananas

Vitamin B7

Dermatitis, enteritis   Raw egg yolk, liver, peanuts, certain vegetables

Vitamin B9

Megaloblast and Deficiency during pregnancy is associated withbirth defects, such as neural tube defects May mask symptoms of vitamin B12 deficiency; other effects. Leafy vegetables, pasta, bread, cereal, liver

Vitamin C

Scurvy Vitamin C megadosage Many fruits and vegetables, liver

Vitamin A

Night-blindness, Hyperkeratosis, and Keratomalacia Hypervitaminosis A Orange, ripe yellow fruits, leafy vegetables, carrots, pumpkin, squash, spinach, liver

Vitamin D

Rickets and Osteomalacia Hypervitaminosis D Fish, eggs, liver, mushrooms

Vitamin E

Deficiency is very rare; mildhemolytic anemia in newborn infants. Increased congestive heart failure seen in one large randomized study. Many fruits and vegetables, nuts and seeds

Vitamin K

Bleeding diathesis Increases coagulation in patients takingwarfarin. Leafy green vegetables such as spinach, egg yolks, liver

Orange vitamin = Solubility in water / Green vitamins = Solubility in fats