What are vitamins?

Most people have heard of vitamin C and its effects upon the body; but how much do you know about other vitamins? How many even are there? And what do they all do?

What are vitamins?

Vitamins are substances that have very important uses in the body. They are used in growth, metabolism and nerve function. (1)

Video outlining the role of vitamins in the body and an interview with Barbara Schneeman, PhD, Director of FDA’s Office of Nutritional Products, who discusses vitamin supplements. Source: FDA

Vitamins can be broken down into two types: fat-soluble and water-soluble.

Fat-soluble vitamins

Vitamins A, D, E and K are examples of fat soluble vitamins. They are carried by fat in the body.

vitamin image

Consuming too many fat-soluble vitamins can, in fact, be harmful. This is because, although it is commonly known that vitamin C cannot be stored by the body, excess fat-soluble vitamins can be stored within the body in fat and liver cells.

Consequently, it is possible to have too high a quantity of vitamins. Moreover, consumption of too many vitamin A and E supplements has been linked to increased risk of premature death. (2)

Water-soluble vitamins

B-complex vitamins and vitamin C are water-soluble vitamins. They are not stored by the body as they dissolve in water. Consequently they are excreted in urine.

Water-soluble vitamins, therefore, need to be consumed every day in order for the body to have a sufficient supply. (3)

How many vitamins are there?

There are 13 known essential vitamins. These include:-

  • Vitamin A
  • B vitamins, which include:
    • Vitamin B1 (thiamin)
    • Vitamin B2 (riboflavin)
    • Vitamin B3 (niacin)
    • Vitamin B6
    • Vitamin B12
    • Folic acid
    • Pantothenic acid (4)
    • Biotin (5)
  • Vitamin C
  • Vitamin D
  • Vitamin E
  • Vitamin K (1)

What roles do vitamins play in the body and where are they found?

Each of the vitamins has different roles and can be found in several places.

Vitamin A

Vitamin A, or retinol as it is also known, has four main functions:

  • It strengthens the immune system against infections (6)
  • It plays an essential role in vision - aiding the body to see in dim light
  • It helps with normal bone growth (2)
  • It keeps the skin, and the linings of the body, healthy (6)

Vitamin A may also help to reduce the risk of cancer, as it is an antioxidant. Consequently it protects the body from free radicals that may harm the body. (2)

You can consume vitamin A from animal products, such as milk, egg yolk and liver; and from fruit and vegetables. (2)

B vitamins

There are 8 B-complex vitamins. They are used by the body to gain energy from food. (3)

Specifically, vitamin B6 is used by the body to store energy from food; whereas vitamin B12 is used by the body to release energy from food and to create red blood cells. (7)

B vitamins also have a few other roles within the body:-

  • They help to control the appetite
  • They aid vision
  • They help to keep the skin healthy
  • They are needed for a healthy nervous system (3)

Several foods contain B-complex vitamins, including:

  • Animal products, such as meat, poultry, fish, milk and eggs
  • Cereal grains
  • Beans
  • Peas
  • Fresh vegetables (3)

Vitamin C

Many people know that vitamin C is important in fighting against infection and protecting against scurvy, but what actually is vitamin C? How does it prevent scurvy? And where is vitamin C found?

Vitamin C is actually ascorbic acid. It is also an antioxidant, which, as previously mentioned, means that it fights free-radicals that may damage DNA. Free-radical damage has been linked to the development of cancer, heart disease and arthritis. (8)

The body needs vitamin C to make collagen, which is a protein found in skin, cartilage, tendons, ligaments and blood vessels. (8)

Specifically, vitamin C is necessary for the formation of the structure of collagen. Normally, vitamin C allows the hydroxylation of the pro-α chains which together form a stable triple-helical procollagen structure, which then assembles into fibrils. (9)

Without sufficient vitamin C, blood vessels, tendons, skin and so forth do not have the support of collagen and thus they are fragile. (9)

Severe deficiency in vitamin C leads to scurvy. (8)

Many people know that vitamin C is found in citrus fruits such as oranges and limes.

British sailors were even known as “limeys”, for they were provided with limes in order to prevent scurvy. (9)

But vitamin C is also found in other foods, including:

  • Asparagus
  • Broccoli
  • Brussel sprouts
  • Cabbage
  • Kiwi fruit
  • Peppers
  • Plantain
  • Sweet potatoes
  • Tomatoes (3, 10)

Vitamin D

Vitamin D’s key function is to control the amount of calcium and phosphate in the body. (11)

Consequently, it is important in the health of bone, teeth and cartilage. (2) Furthermore, a deficiency in vitamin D can lead to rickets in children and osteomalacia in adults. (11)

The body’s main source of vitamin D is through sunlight. (7)

However, vitamin D can also be provided through foods, including:-

  • Oily fish
  • Eggs
  • Liver
  • Fortified foods such as breakfast cereals, fat spreads and so forth. (7, 11)

Vitamin E

Vitamin E helps to protect cell membranes. (12) It is also involved in blood clotting – specifically vitamin E stops blood from clotting. (2)

Consequently, a deficiency in vitamin E has been linked to nervous, vascular and reproductive system problems. Such a deficiency is, however, rare. (2)

Vitamin E is found in the following:-

  • Plant oils, such as olive, soya and corn oil
  • Wheat germ – which is contained in cereals (12)
  • Seeds, such as sunflower seeds
  • Nuts, such as hazelnuts, peanuts and pistachio nuts
  • Prawns (2)

Vitamin K

Vitamin K’s main role is in blood clotting, which means that it is very important in wound healing. (13)

Specifically, vitamin K is one of 13 proteins that are involved in a cascade that causes the blood to clot. (14)

Vitamin K is also important for the role it plays in keeping bones healthy. (2)

Researchers have found that vitamin K can increase bone density in people with osteoporosis, and that it can also reduce fracture rates. (15)

Vitamin K is mainly found in green leafy vegetables such as spinach, broccoli and cabbage. It is also found in some vegetable oils such as soybean and rapeseed. Also it is found in some cereals. (2, 13)

Some babies are given are given vitamin K injections at birth. This is because during pregnancy little vitamin K reaches the baby as it cannot cross the placenta. (16)

If the newborn baby does not have enough vitamin K, haemorrhagic disease, a rare bleeding disorder, can result. If the parent does not wish the child to have an injection, then oral doses may be provided. (17)

April Cashin-Garbutt

Written by

April Cashin-Garbutt

April graduated with a first-class honours degree in Natural Sciences from Pembroke College, University of Cambridge. During her time as Editor-in-Chief, News-Medical (2012-2017), she kickstarted the content production process and helped to grow the website readership to over 60 million visitors per year. Through interviewing global thought leaders in medicine and life sciences, including Nobel laureates, April developed a passion for neuroscience and now works at the Sainsbury Wellcome Centre for Neural Circuits and Behaviour, located within UCL.


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