Last updated by Dr Sarah Brewer on
Thirteen vitamins are essential for life, although they are only needed in tiny amounts. Most cannot be synthesized in the body at all, such as vitamin C, but a few such as vitamin D and niacin, are made in tiny amounts that are usually too small to meet your needs.
Vitamins are involved in all your metabolic reactions from digestion, energy production and hormone responses to immunity, growth and repair. Good dietary intakes are therefore vital.
The vitamin content of food is generally similar whatever the source, as the plants (and some animals) synthesise these themselves. If fruit is picked when unripe, however, its vitamin content usually falls compared with if it is allowed to mature in full contact with the resources of the parent plant.
Vitamins are generally ‘delicate’ in chemical terms and degrade on prolonged contact with light and air, or if heated. Fresh produce that is eaten as soon as possible after harvesting, and with minimal processing, is therefore the most nutritious.
Despite their importance for health, vitamin deficiencies are common. Vitamin intakes that are consistently below recommended levels can lead to non-specific symptoms such as dry, itchy skin, lack of energy and reduced immunity.
A scientific review of over 150 clinical trials published in the Journal of the American Medical Association concluded that lack of many vitamins is a risk factor for heart disease, stroke, some cancers, osteoporosis and other major chronic health problems. They pointed out the dangers of excess vitamin intakes, too, but in an accompanying paper, the authors actually state that ‘Pending strong evidence of effectiveness from randomised trials, it appears prudent for all adults to take vitamin supplements.” For those who find this difficult to believe, click here for the reference.
How quickly a particular vitamin deficiency leads to health problems depends on the size of your body stores and how quickly your supplies run out. Vitamins that are fat-soluble, such as vitamins A, D, E and K are stored more easily in the liver than those that are water-soluble such as folate and vitamin C which are easily lost in the urine. The exception to this rule is vitamin B12 which is stored in the liver, too.
To read more about each vitamin, click on the following links to find out why you need them, where to find them in your diet, how much of each you need, the symptoms that can occur when you do not get enough, and the research relating to their health benefits.
A – Z of Vitamins
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