Some science behind the scenes

Vitamins

Vitamins are organic compound required as a nutrient in tiny amounts by an organism.  In other words, 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 environment, usually from food and drink. 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 D are required in the human diet only in certain circumstances.

By convention, the term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids (which are needed in larger amounts than vitamins), nor does it encompass the large number of other nutrients that maintain health, but are otherwise required less often.

Background

The term vitamin was derived from "vitamine," a combination word made up by Polish scientist Casimir Funk from vital and amine, meaning amine of life, because it was suggested in 1912 that the organic micronutrient food factors that prevent beriberi and perhaps other similar dietary-deficiency diseases might be chemical amines. This proved correct for the micronutrient class, and the word was shortened to vitamin.

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. Some have hormone-like functions as regulators of mineral metabolism (e.g., vitamin D), or regulators of cell and tissue growth and differentiation (e.g., some forms of vitamin A). Others function as antioxidants (e.g., vitamin E and sometimes vitamin C). The largest number of vitamins (e.g., B complex vitamins) function as precursors for enzyme co-factors, 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 co-enzymes, 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.

For the most part, vitamins are obtained with food, but a few are obtained by other means. For example, microorganisms in the intestine — commonly known as "gut flora" — produce vitamin K and biotin, while one form of vitamin D is synthesized in the skin with the help of the natural ultraviolet wavelength of sunlight. Humans can produce some vitamins from precursors they consume. Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan.

Vitamins are essential during the growth of a baby, but even once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multi-cellular organism; they also enable a multi-cellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for respiration.

Thirteen vitamins are universally recognized at present.  The table below lists them and show some common sources.  More details are provided in the suppression section, where each vitamin is listed

Vitamin

Some example food sources

Vitamin A (Retinol)

Vitamin A is found naturally in a vast number of foods – cod liver oil, liver, leafy green vegetables, orange vegetables (carrots, pumpkin, squash, sweet potatoes), dairy products (butter, cheese, milk), eggs, fruit [melons, apricots, papaya, mango, tomatoes etc]  and even seaweed 

Vitamin B1 (Thiamine)

Thiamine is found in yeast, yeast extract, pork, whole cereal grains and wheat germ, oatmeal, flax, and sunflower seeds, brown rice, whole grain rye, asparagus, kale, cauliflower, potatoes, oranges, liver and eggs. 

Vitamin C (Ascorbic acid)

The richest natural sources of Vitamin C are practically all fruits eg citrus fruits, kiwi fruit, lychees, elderberries, papayas, strawberries, plums, gooseberries, rose hips, chili peppers, red peppers, guava, blackcurrants, melon, raspberry, blackberries, mango, tomatoes, cranberry, blueberry, grapes, apricots, banana, avocado, cherry, peach, pear, apple);  herbs (especially parsley); onions and garlic;  and practically all vegetables e.g. brussel sprouts, broccoli, kale, spinach, cabbage, potatoes, carrots, lettuce, beetroot, aubergine etc.  Raisins and figs are also good sources.  It is also present in liver, oysters, cod roe, goat’s milk, camel’s milk, lamb’s heart, lamb’s tongue and human milk. 

Vitamin D (Calciferol)

Vitamin D is found in only a few dietary sources. Sunlight exposure is the primary source of vitamin D.  Other sources are fungi (for example shiitake and portabella exposed to sunlight); alfalfa; fish liver oils; and fatty fish eg mackerel, salmon, sardines, tuna, eel, catfish; beef liver and eggs 

Vitamin B2 (Riboflavin)

Riboflavin is found in asparagus, popcorn, bananas, persimmons, okra, chard, cottage cheese, milk, yogurt, meat, eggs, fish, and green beans. Other sources are cheese, leafy green vegetables, liver, kidneys, legumes, tomatoes, yeast, mushrooms, and almonds  Riboflavin is destroyed by exposure to ultraviolet light, so milk sold in transparent (glass/plastic) bottles will likely contain less riboflavin than milk sold in opaque containers 

Vitamin E (Tocopherol)

Vegetable oils; nuts and nut oils;  green leafy vegetables; tomatoes; squashes; sweet potatoes; fruits [especially mangoes and papayas], avocados; some fish 

Vitamin B12 (Cobalamins)

Vitamin B12 is found in most animal derived foods, including fish and shellfish, meat (especially liver), poultry, eggs, milk, and milk products. However, the binding capacity of egg yolks and egg whites is markedly diminished after heat treatment.  It is very easy for vegans to become vitamin B12 deficient 

Vitamin K1 (Phylloquinone)

Vitamin K1, is synthesized by plants, and is found in highest amounts in green leafy vegetables because it is directly involved in photosynthesis. It may be thought of as the "plant form" of vitamin K.

Vitamin B5 (Pantothenic acid)

Small quantities  of pantothenic acid are found in nearly every food.  The major food source of pantothenic acid is meat. High amounts are also found in whole-grain cereals,  broccoli, alfalfa, legumes, eggs, royal jelly, avocado and yogurt.  Mushrooms, molasses and yeast also contain significant amounts. 

Vitamin B7 (Biotin)

Biotin is consumed from a wide range of food sources in the diet, but few are particularly rich sources. Foods with a relatively high biotin content include Swiss chard, raw organic egg yolk, liver, Saskatoon berries, and leafy green vegetables.

Vitamin B6 (Pyridoxine)

Vitamin B6 occurs in many foods.  Good sources include meats, whole grain products, vegetables,  nuts, milk and bananas. Cooking, storage, and processing may deplete the vitamin content in some foods by as much as 50%. Plant foods lose the least during processing.  Milk can lose 30-70% of its vitamin B6 content when dried.  Freezing and canning are other food processing methods that result in the loss of vitamin B6 in foods.

Vitamin B3 (Niacin)

Niacin is found in liver, heart, kidney, chicken, beef, fish, eggs, venison, avocados, dates, tomatoes, leafy vegetables, broccoli, carrots, sweet potatoes, asparagus, nuts, whole grain products, legumes, mushrooms and brewer’s yeast.  It can also be found in peanut butter, soy sauce, vegemite, marmite and tofu.  It  is also synthesized from tryptophan, an essential amino acid found in most forms of protein.

Vitamin B9 (Folic acid)

Leafy green vegetables, fortified cereals and bread; legumes such as dried or fresh beans, peas and lentils; egg yolks; baker's and brewer’s yeast [and thus beer];  sunflower seeds; Liver; Kidney; some fruit [citrus fruits, melons, bananas, raspberries, strawberries, tomatoes]