Vitamins : Definition and Types.

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 Vitamins are organic compounds that are essential in small amounts for various physiological functions in the body. They cannot be synthesized in sufficient quantities by the body (or at all), so they must be obtained through the diet. Vitamins play crucial roles in processes such as energy production, immune function, bone health, and cell repair.

There are two main types of vitamins:

  1. Fat-soluble vitamins: These include vitamins A, D, E, and K. They are absorbed with dietary fat and stored in the liver and fatty tissues for later use.
  2. Water-soluble vitamins: These include the B-vitamins (e.g., B1, B2, B6, B12) and vitamin C. They are not stored in the body and are excreted through urine, so regular intake is necessary.

Each vitamin has a specific role, and deficiencies or excesses of certain vitamins can lead to health problems.


Fat-soluble vitamins are vitamins that dissolve in fats and oils and are absorbed along with dietary fat. They are stored in the body's fatty tissues and liver, and unlike water-soluble vitamins, they are not excreted easily, meaning they can accumulate to potentially toxic levels if consumed excessively. The four main types of fat-soluble vitamins are:

1. Vitamin A (Retinol)

  • Function: Essential for vision, immune function, skin health, and cell growth. Vitamin A plays a role in maintaining healthy mucous membranes and is also important for reproduction and cellular communication.
  • Sources: Liver, fish oils, dairy products, eggs, and plant-based sources like carrots, sweet potatoes, spinach, and kale (as provitamin A carotenoids like beta-carotene).

2. Vitamin D

  • Function: Crucial for calcium absorption and bone health. It helps maintain proper immune function and regulates the growth and repair of cells. It also plays a role in mood regulation and the reduction of inflammation.
  • Sources: Sunlight (which helps the body synthesize vitamin D), fatty fish (salmon, mackerel), fortified dairy products, egg yolks, and mushrooms.

3. Vitamin E (Tocopherol)

  • Function: Acts as an antioxidant, protecting cells from oxidative damage. It also supports immune function and skin health, and is involved in preventing blood clotting.
  • Sources: Nuts, seeds, vegetable oils (like sunflower, olive, and canola oil), leafy green vegetables, and fortified cereals.

4. Vitamin K

  • Function: Vital for blood clotting (hemostasis) and bone health. It helps the body produce proteins required for blood clotting and bone metabolism.
  • Sources: Leafy green vegetables (like kale, spinach, and broccoli), fermented foods, dairy products, and some vegetable oils.

These vitamins are generally absorbed in the small intestine with dietary fats and can be stored in the liver and fatty tissues, where they can be drawn upon when needed. It's important to balance intake of fat-soluble vitamins, as both deficiencies and excessive amounts can lead to health issues.


Water-soluble vitamins are vitamins that dissolve in water and are not stored in the body for long periods. Instead, they are excreted through urine, so they need to be replenished regularly through diet. These vitamins play vital roles in energy production, immune function, and the maintenance of healthy skin, nerves, and blood cells.

The main types of water-soluble vitamins include the B-vitamins and vitamin C.

1. Vitamin B1 (Thiamine)

  • Function: Helps convert carbohydrates into energy, supports nerve function, and plays a role in muscle function and heart health.
  • Sources: Whole grains, pork, legumes, seeds, nuts, and fortified cereals.

2. Vitamin B2 (Riboflavin)

  • Function: Involved in energy production and the metabolism of fats, proteins, and carbohydrates. Also helps maintain healthy skin, eyes, and nervous system.
  • Sources: Milk, eggs, lean meats, green leafy vegetables, and fortified cereals.

3. Vitamin B3 (Niacin)

  • Function: Supports energy production by helping the body convert carbohydrates, fats, and proteins into usable energy. Also important for skin health, digestive function, and nervous system health.
  • Sources: Meat, poultry, fish, whole grains, peanuts, and legumes.

4. Vitamin B5 (Pantothenic Acid)

  • Function: Plays a key role in energy metabolism and the synthesis of coenzyme A, which is involved in the synthesis of steroid hormones, neurotransmitters, and hemoglobin.
  • Sources: Chicken, beef, potatoes, oats, tomatoes, and whole grains.

5. Vitamin B6 (Pyridoxine)

  • Function: Important for protein metabolism, brain development, and the production of neurotransmitters. It also helps in the formation of red blood cells and the regulation of blood sugar levels.
  • Sources: Fish, poultry, potatoes, chickpeas, bananas, and fortified cereals.

6. Vitamin B7 (Biotin)

  • Function: Essential for the metabolism of fats, carbohydrates, and proteins, and supports healthy hair, skin, and nails.
  • Sources: Eggs, almonds, spinach, sweet potatoes, and certain fish.

7. Vitamin B9 (Folate or Folic Acid)

  • Function: Crucial for DNA synthesis, cell division, and growth. Especially important during pregnancy to prevent neural tube defects in the developing fetus.
  • Sources: Leafy green vegetables, citrus fruits, beans, lentils, and fortified grains.

8. Vitamin B12 (Cobalamin)

  • Function: Vital for the production of red blood cells, the maintenance of the nervous system, and the synthesis of DNA.
  • Sources: Animal products such as meat, fish, poultry, dairy, and fortified cereals (vegetarians and vegans may need supplements).

9. Vitamin C (Ascorbic Acid)

  • Function: Acts as an antioxidant, supports the immune system, promotes wound healing, aids iron absorption, and contributes to the health of skin, cartilage, teeth, and bones.
  • Sources: Citrus fruits (oranges, lemons), strawberries, kiwi, bell peppers, broccoli, tomatoes, and spinach.

Key Points About Water-Soluble Vitamins:

  • Absorption and Excretion: Water-soluble vitamins are absorbed directly into the bloodstream from the intestines. Since they are not stored in large quantities, they are excreted through urine when the body has more than it needs.
  • Deficiency Risks: Because they are not stored in the body, deficiencies in water-soluble vitamins can develop more quickly compared to fat-soluble vitamins, especially if dietary intake is insufficient.
  • Toxicity: Unlike fat-soluble vitamins, toxicity from water-soluble vitamins is rare since excess amounts are generally excreted, but very high doses of certain vitamins (especially B6 or niacin) can lead to health problems.

To maintain optimal health, a balanced diet with adequate amounts of these water-soluble vitamins is important.

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