Vitamins: Definition types functions and Sources

Definition: Vitamins are organic compounds required by the body in small amounts for metabolism, for protection, for
maintenance of health and proper growth
They cannot be synthesized by the body. Must be obtained by outside sources like diet, rumen of
bacteria & sun.
Vitamins also assist in the formation of hormones, blood vessels, nervous system chemicals and genetic materials
They generally act as catalysts, combining with proteins to create metabolically active enzymes that are essential for life reactions
Without enzymes, many of the reactions essential to life would slow down or cease.


Vitamins are of different chemical nature. These are alcohols, aldehydes, organic acids, their derivatives and
nucleotide derivatives.


  • Vitamins are classified according to their ability to be absorbed in fat or water
  • 1. Fat Soluble Vitamins: these are oily and hydrophobic compounds, they are stored in the liver and not excreted out of the body. Bile salts and fats are needed for their absorption. Vitamins A,D,E and K are fat soluble
  • 2. Water Soluble Vitamins: Vitamin B complex and Vitamin C are water soluble. They are not stored
    in the body, therefore are required daily in small amounts

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Fat-soluble vitamin

Fat-soluble vitamins are stored in the fat cells and as the name suggests, these vitamins require fat in order to be absorbed. Vitamin A, D, E and K are fat-soluble vitamins.

Water-soluble vitamin

Water-soluble vitamins are not stored in our body as its excess gets excrete through the urine. Therefore, these vitamins need to be replenished constantly. Vitamin B and C are water-soluble vitamins.

Sources of Vitamins

The human body is so designed that it takes what it needs from the food we eat and then it passes out waste as excreta.

These organic substances are abundantly found in both plants and animals source and play a vital role in both growth and development and optimal health.

Listed below are the different types of vitamins along with their sources.

The best sources of fat-soluble vitamins include:

  • Vitamin A: Found in potato, carrots, pumpkins, spinach, beef and eggs.
  • Vitamin D: Found in fortified milk and other dairy products.
  • Vitamin E: Found in fortified cereals, leafy green vegetables, seeds, and nuts.
  • Vitamin K: Found in dark green leafy vegetables and in turnip or beet green.

vitamin C are abundantly found in all citrus fruits. Other sources of Vitamin B and C include:

  • Vitamin B1 or Thiamin: Found in pork chops, ham, enriched grains and seeds.
  • Vitamin B2 or Riboflavin: Found in whole grains, enriched grains and dairy products.
  • Vitamin B3 or Niacin: Found in mushrooms, fish, poultry, and whole grains.
  • Vitamin B5 or Pantothenic Acid: Found in chicken, broccoli, legumes and whole grains.
  • Vitamin B6 or Pyridoxine: Found in fortified cereals and soy products.
  • Vitamin B7 or Biotin: Found in many fruits like fruits and meats.
  • Vitamin B9 or Folic Acid: Found in leafy vegetables.
  • Vitamin B12: Found in fish, poultry, meat and dairy products.
  • Vitamin C: Found in citrus fruits and juices, such as oranges and grapefruits.


Read Also:  Proteins: Definition structure and functions

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