What are vitamins?

Diet


Emily Condon
BSc (Hons) Biological Sciences

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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. 

  • Vitamin A: For adults (19-64 years) 0.7 mg a day for men and 0.6 mg a day for women is recommended.
  • B1 (thiamin): For adults, 1mg a day for men and 0.8 mg a day for women is recommended.
  • B2 (riboflavin): For adults, 1.3 mg a day for men and 1.1 mg a day for women is recommended.
  • B3 (niacin): For adults, 16.5 mg a day for men and 13.2 mg a day for women is recommended.
  • B5 (pantothenic acid): Because pantothenic acid is found in many food types, you should be able to get all you need from your daily diet. B5 can't be stored in the body, so you need it in your diet every day.
  • B6 (pyridoxine): For adults, 1.4 mg a day for men and 1.2 mg a day for women is recommended.
  • B7 (biotin): You should be able to get all the biotin you need by eating a varied and balanced diet. Taking too many biotin supplements may be harmful but taking 0.9 mg or less a day of biotin supplements is unlikely to cause any harm.
  • B9 (folate): Adults need 200 mcg of folic acid a day. It can't be stored in the body, so you need it in your diet every day. Most people should be able to get the amount they need by eating a varied and balanced diet.

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. 

  • B12 (cobalamin): Adults need about 1.5mcg a day of vitamin B12. If you eat meat, fish or dairy foods, you should be able to get enough vitamin B12 from your diet.

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.  

  • Vitamin C: Adults need 40 mg of vitamin C a day. Vitamin C is not stored in the body, so you need it in your diet every day.
  • Vitamin D: It is difficult to get enough vitamin D from food alone. Because of this many of us in the UK are deficient in vitamin D. Everyone (including pregnant and breastfeeding women) should look at taking a daily 10mcg vitamin D supplement during the autumn and winter.
  • Vitamin E: For adults, 4 mg a day for men and 3mg a day for women is recommended.
  • Vitamin K: Adults need around 1 mcg a day of vitamin K for each kilogram of their body weight. Any vitamin K your body doesn't require immediately is stored in the liver, so you don't need i

How are your vitamin levels?

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