Vitamins

Vitamins are naturally occurring nutrients which, even though they are only needed in tiny amounts, are essential for life. The word vitamin was first used by Casimir Funk, a Polish chemist, in 1911, as a contraction of two words: vital (meaning life) and amine (a chemical group originally incorrectly thought to occur in all vitamins).

There are 13 major vitamins that can't be synthesized in the body (vitamin C is one), or which can only be made in tiny amounts (vitamin D, niacin) that are too small for most people's needs. You therefore need to obtain adequate amounts of vitamins from your food and by taking dietary supplements.

Most vitamins act as essential intermediaries or catalysts to keep the body's metabolic reactions running smoothly and efficiently. These reactions include those responsible for:

digestion
converting food into energy
cell division and growth
tissue repair
transporting oxygen and wastes in the circulation
immunity
mental alertness
making hormones
reproduction
protecting the body from poisons
neutralizing the harmful by-products of metabolism such as
free radicals

If your intake of any vitamin is consistently too low, your metabolism will not function smoothly, and relatively common problems can occur such as:

dry, itchy skin
tiredness and lack of energy
increased susceptibility to infection
reduced fertility
poor wound healing

How quickly these deficiencies will lead to problems depends on how quickly your store of a particular vitamin runs out. Symptoms of folic acid deficiency may show within weeks, for example, as very little is stored in the body. Stores of vitamin B12 however are large, and it can take years for deficiency to show up.

In general, vitamins that are fat-soluble are stored more easily in the body (e.g. in the liver) than water-soluble ones that are easily lost in urine. The fat-soluble vitamins are A, D, E and K, and the water-soluble vitamins are the B and C group whose levels (with the exception of vitamin B12) must be continually replenished from the diet.