What Are Vitamins? What Are Their Different Types, Sources And Functions?

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Ever since childhood, we’ve likely been told by our mothers to drink glass of orange juice with breakfast, or have a handful of carrots as a snack. If we dare to say no, they would launch into horror stories of needing glasses, losing our eyesight, or even going blind! Now, looking back, I understand why my mother forced certain fruits and vegetables down my throat.

Basically, they’re rich in certain compounds that our body needs for normal development and growth. Our body is brilliant when it comes to being a self-reliant machine and producing almost everything that we need, but when it comes to these compounds, the body falls short and needs a little help from our diet. These compounds, though needed in minute quantities, are absolutely essential for our bodies. As you may have guessed by now, these are called vitamins.

What are vitamins?

To quickly summarize the above information into a formal definition, it is safe to say that Vitamins are:

  • Organic compounds distinct from fats, carbohydrates, and proteins and are not synthesized by our body in amounts needed to meet our physiological demands.
  • They are natural components of foods, in which they are found in minute quantities.
  • They are essential, but needed in only minute amounts by our bodies for growth, development, etc.
  • Their absence or underutilization in our body leads to deficiency syndromes manifested by various clinical symptoms.

Sometimes, even our dietary intake is unable to provide the required amounts of vitamins, in which case we need to consume vitamin pills to ensure the normal functioning of our body. If you compare our bodies to a fully functional household, you can think of vitamins as the butlers or maids who come from outside the house, but are critical for the smooth functioning of the household.

Types of vitamins and their stability

So far, thirteen substances have been recognized as vitamins. These include A, C, D, E, and K, as well as the B vitamins: thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxal (B6), cobalamin (B12), biotin, and folate/folic acid. Vitamins are classified based on their solubility as fat-soluble or water-soluble vitamins. The fat-soluble vitamins include vitamin A, D, E and K, whereas Vitamin B1, B2, B3, B5, B6, B7, B9, B12, and C are water-soluble vitamins. Fat-soluble vitamins are stored in the fat tissues of the body and remain in the adipose tissues until they’re needed. Water-soluble vitamins are poorly stored in the body, so if a person’s intake is greater than what is required by the body, these vitamins are excreted in the urine. Since fat-soluble vitamins are not excreted in a similar fashion, an over-consumption of fat-soluble vitamins leads to hypervitaminosis. Fat-soluble vitamins exhibit some common traits, e.g., they’re all composed either entirely or primarily of five-carbon isoprenoid units derived from acetyl-CoA. On the other hand, water-soluble vitamins lack any similarity of structure and are a very heterogeneous group of substances.

Each vitamin compound possesses different physical and chemical properties, many of which are affected by the conditions in which they are produced and stored. A vitamin that is properly stored is capable of maintaining its full biological potential for years. Factors that contribute to losses of vitamin properties are encountered at different stages of production, storage and meal preparation; these factors include pH value, oxygen, light, temperature, water content and interactions with other vitamins.

Sources and Functions

Our bodies are incapable of producing vitamins in adequate quantities needed for proper growth and development, but fortunately, vitamins occur naturally in many foods that we consume on a daily basis. Certain foods are rich in certain vitamins and lack others, so it’s important to know what food provides which vitamins so we can make a conscious effort to consume a balanced diet and fulfill our bodily requirements.

Vitamin A

Many foods contain the fat-soluble vitamin A, usually in the form of retinyl acetate or retinyl palmitate (pre-formed vitamin A), beta-carotene (provitamin A) or some combination of both.

Sources – Foods rich in vitamin A include sweet potatoes, carrots, pumpkins, spinach, mangoes, broccoli, apricots, liver, eggs, shrimp, fish, fortified milk and butter.

Vitamin A in food Natural products rich in vitamin A as tangerine, red pepper, parsley leaves, dried apricots, carrots, broccoli, butter, yellow cheese, milk, egg yolk and cod liver oil. - Image( Evan Lorne)s

(Photo Credit : Evan Lorne/Shutterstock)

Benefits and deficiencies – Vitamin A is essential for good vision, boosts our immune system, and helps our lungs, kidneys and heart function properly. However, it is mostly associated with eye issues and is estimated to affect millions of children worldwide; the most prominent symptoms of a vitamin A deficiency are night blindness and xerophthalmia. In fact, a deficiency of vitamin A is now recognized as the most important cause of childhood blindness in developing countries. In short, eat all the carrots your mother has to offer so you can look at the world without any trouble!

Vitamin B

This group includes more than one vitamin and they are named as follows:

  • Vitamin B1 (Thiamin)
  • Vitamin B2 (Riboflavin)
  • Vitamin B3 (Niacin)
  • Vitamin B5 (Pantothenic acid)
  • Vitamin B6 (Pyridoxine)
  • Vitamin B7 (Biotin)
  • Vitamin B9 (Folic acid)
  • Vitamin B12 (Cobalamin)

Sources – Meat, poultry, fish, milk, cheese, eggs, fortified cereals, fortified soy milk, legumes, tofu, green leafy vegetables, grains, and cereals are all good dietary sources of vitamin B.

Benefits and deficiencies

Vitamins B1, B2, B3, and B5 generally help in converting the food we consume into energy. These vitamins also play an important role in maintaining healthy skin, hair, muscles, and brain function. A deficiency of vitamin B1 causes a disease called beriberi, although it is rare in developed countries, as the food there is more commonly fortified and enriched with vitamins. Vitamin B5 or pantothenic acid also helps in making neurotransmitters, hemoglobin, steroid hormones and lipids.

Vitamin B6 and B12 aid in lowering homocysteine levels and help in reducing the risk of heart problems. Vitamin B6 also plays an important role in helping us sleep better, regulating our mood and appetite; a deficiency of this vitamin can cause convulsions and sometimes neurological disorders. Vitamin B12 encourages the normal growth of nerve cells and helps in the generation of red blood cells. A person with a deficiency in vitamin B12 suffers from pernicious anemia. Vitamin B7, apart from converting food into energy, is also needed for healthy bones and hair. Vitamin B9 or folic acid is extremely essential during pregnancy, as it prevents the fetus from developing neural tube defects, i.e., brain and spinal birth defects. Women of childbearing age should regularly consume folic acid to prevent such defects.

Vitamin C

Vitamin C in fruits and vegetables. Natural products rich in vitamin C as oranges, lemons, dried fruits rose, red pepper, kiwi, parsley leaves, garlic, bananas, pears, apples, walnuts, chili. - Image( Evan Lorne)s

(Photo Credit : Evan Lorne/Shutterstock)

We often go to our dentist complaining of bleeding gums and fear what the dentist may say next. Well, usually, all that is required is a supplement of ascorbic acid or vitamin C to improve the situation. Vitamin C plays an important role in keeping our gums and blood vessels in good shape. It also strengthens our immunity and prevents us from getting sick too frequently.

Sources – Fruits and fruit juices (especially citrus), potatoes, broccoli, bell peppers, spinach, strawberries, tomatoes, and Brussels sprouts are all Vitamin C-rich sources.

Benefits and deficiencies

(Photo Credit : Aleksandr Markin/Shutterstock)

As mentioned earlier, vitamin C helps to keep our blood vessels healthy and does so by making collagen, a connective tissue that supports blood vessel walls and helps in healing wounds. Vitamin C also acts as an antioxidant, strengthens our immune system, and even helps to protect against certain cancers. A deficiency in vitamin C can be identified by the presence of dry, bumpy skin that is also prone to bruising and demonstrates slow wound healing as a result of hampered collagen production. A severe form of vitamin C deficiency is called scurvy, which is characterized by swollen, bleeding gums that can eventually lead to tooth loss!

Vitamin D

This is a fat-soluble vitamin that helps the body absorb calcium. Given that calcium is the main building block of our bones, vitamin D has a direct impact on the health and strength of our bones and teeth. It is also needed by our muscles to move and by our nerves to carry messages.

Vitamin D concept - Image(Pixelbliss)

(Photo Credit : Pixelbliss/Shutterstock)

Sources – Very few foods naturally have vitamin D. It is primarily synthesized by our body when we directly expose our skin to the sun. If you’re not able to meet your requirement for vitamin D in this way, you may need to supplement your intake through your diet or supplements.

Benefits and deficiencies

Vitamin D helps to regulate and maintain normal levels of calcium and phosphorus, which in turn strengthens our bones and teeth. People who fail to maintain their vitamin D levels tend to develop brittle, soft bones that are prone to fracture. If this condition strikes during childhood, it results in rickets, whereas if it hits you in adult life, you may develop conditions like osteomalacia and osteoporosis. It’s important to remember that vitamin D is a fat-soluble vitamin and does not get excreted if it accumulates in the body. This often leads to hypervitaminosis or vitamin D toxicity, which may cause you to experience nausea, vomiting, poor appetite, weakness, weight loss, constipation, confusion, disorientation, etc. Remember that such toxicity usually only results from an excessive use of supplements, not by overexposure to sunlight, as our bodies know how to limit and regulate its sun-induced synthesis of vitamin D.

Vitamin E

Foods rich in vitamin E such as wheat germ oil, dried wheat germ, dried apricots, hazelnuts, almonds, parsley leaves, avocado, walnuts, pumpkin seeds, sunflower seeds, spinach and green paprika - Image( Evan Lorne)s

(Photo Credit : Evan Lorne/Shutterstock)

Vitamin E is a fat-soluble vitamin that mainly acts as an antioxidant. For those who don’t know about antioxidants, allow me to explain. When the food we consume is converted into energy, free radicals are formed. These free radicals are unstable atoms with unpaired electrons. They are also always on the lookout for an electron so it can pair up and attain stability; while doing so, they hunt and scavenge the body, resulting in damage and inflammation. Antioxidants play an important role by providing these unstable free radicals with an electron so that they are paired, happy and less destructive to our bodies. Free radicals are generally associated with aging, while Vitamin E, in this case, is associated with anti-aging effects on our skin, which is why it is included in so many skin care creams.


Leafy green vegetables, whole grains, nuts, vegetable oils like sunflower, canola and olive oil, salad dressings, etc. are all good options for you to get your dose of vitamin E.

 Benefits and deficiencies

Apart from stabilizing free radicals through antioxidant action, vitamin E also strengthens the immune system and helps widen blood vessels, thereby preventing blood clots. Some studies have also suggested that vitamin E might help to prevent or slow down the onset of Alzheimer’s disease. A deficiency of vitamin E is very rare and usually happens in conditions where fat is not being absorbed properly, such as in the case of Crohn’s disease. Signs of Vitamin E deficiency include a weakened immune system, nerve and muscle damage, and a loss of sensation in the arms and legs.

Vitamin K

This is a fat-soluble vitamin required by our body’s clotting mechanism. It activates proteins and calcium, which are essential for blood clotting. With a good amount of vitamin K in your system, you don’t need to worry about bleeding out every time you get a cut.


Cabbage, eggs, milk, liver, sprouts, kale, spinach, broccoli and other green vegetables are excellent dietary sources of vitamin K.

 Benefits and deficiencies

Apart from keeping our clotting system up and running, vitamin K also helps keep our bones strong and makes us less prone to hip fractures and osteoporosis. Vitamin K deficiency makes people more prone to bruising and bleeding, since a lack of vitamin K will make your blood take longer to clot. Caution should be exercised with regards to the intake of vitamin K if you’re on blood thinners, as too little vitamin K can cause bleeding, while an excess of it will cause blood clots.


Based on all of the above information, it’s clear that a healthy balanced diet will lead to a healthy and happy body. These vitamins, though needed in minute quantities, are extremely essential aides for our body. Consistently eating vitamin-rich foods like fruits, vegetables, and whole grains will help lower your risk for conditions such as heart disease, stroke, diabetes, bone disorders and certain forms of cancer!


  1. The Vitamins By Gerald F. Combs
  2. Vitamins By Wilhelm Friedrich
  3. National Institutes Of Health (NIH)
  4. Harvard University
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About the Author:

Dr. Maneka Vig is an experienced dental surgeon with 8 years of dental practice behind her. She completed her Bachelors in Dental Surgery (BDS) from Maharashtra University of Health Sciences in India and ran her own dental practice for many years. She then spearheaded the branch operations for one of India’s largest dental chains as a head dentist for a designated branch wherein she was responsible for rendering treatment, managing operations of the practice and headed a team of efficient doctors. Being passionate about science and academia, she ventured into medical writing and worked with a reputed healthcare communications firm.

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