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What are vitamins?
Vitamins are a group of organic compounds present in small amounts in a variety of natural foods. There are currently 13 recognised vitamins that are essential for supporting the normal functioning of the body: vitamin A, thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9) and cobalamin (B12), C, D, E, K. When a vitamin is absent from the diet, a deficiency will occur.
We need to obtain vitamins from our diet because the body cannot synthesise them quickly enough to meet our daily needs. Vitamins are either fat soluble or water soluble depending on whether they dissolve best in either water or lipids. The 4 fat-soluble vitamins are A, D, E and K. When there are excess levels of fat-soluble vitamins in the body, they are stored in fat cells. These vitamins also require fat to be absorbed. In contrast, the body does not store water-soluble vitamins. The body excretes any water-soluble vitamins that it cannot use.
Recommended daily allowance
The RDA (recommended dietary allowance) and the AI (adequate intake) are the advised amounts of a vitamin you need to stay well-nourished and avoid a deficiency developing. There are different recommendations depending on sex and age. The UL (tolerable upper intake level) is the maximum amount of a vitamin advised to avoid the risk of an overdose or serious side effects occurring.
The NHS recommends the following RDA for the 13 essentials vitamins.
Pregnant women are recommended to supplement 400 mcg folic acid daily from the time you stop using contraception until you're 12 weeks pregnant. This is to help prevent birth defects, such as spina bifida.
But as vitamin B12 isn't found naturally in foods such as fruit, vegetables and grains, vegetarians and vegans may not get enough of it. Dried yeast flakes are a good dietary source for vegans.