Vitamins and their deficiency disorders

We all are familiar with the basic nutrient vitamin but it is important to understand various types of vitamins and their functions, sources and the deficiency diseases they cause. Vitamins are one of the micromolecules required in small quantities but they are essential for normal metabolism and health. They are in existing in a wide range of foods especially in the green leafy vegetables and fruits. Vitamins are mainly classified into two major groups, fat-soluble and water-soluble vitaminsFat-soluble vitamins are vitamins A, D, E and K and the water-soluble vitamins include vitamin B complex and vitamin C. B-complex is further divided into B1, B2, B5, B6, B9 and B12. Let us understand the fat-soluble and water-soluble vitamins in detail.



Fat-soluble vitamins

Fat-soluble vitamins are called so because they are stored along with the lipids found in the liver. They are essentially important micronutrients requiring bile juice for their absorption. Fat-soluble vitamins are absorbed from the small intestine and are classified into vitamins A, D, E, and K.



Vitamin A (retinol)

Vitamin A is essential for our visual system. It is richly found in foods such as yellow fruits, cream, egg yolk, liver, fish oil, milk and milk products including cheese and butter. The vitamin is generally known as carotene and the recommended daily dietary requirement of vitamin A is in an adult is 600 to 700 μg, however, it varies for different age groups.  Vitamin A is crucial for the formation of the light-sensitive pigment called rhodopsin (visual purple) found in the retina of our eye. It also assists in the cellular growth and differentiation of fast-growing cells like epithelial cells which cover skin and some vital organs. The vitamin also aids in the promotion of immunity and defence against infection. To some extent, they participate in the promotion of growth. Furthermore, the deficiency of vitamin A causes night blindness due to the abnormal retinal pigment and the condition is otherwise called nyctalopia. Other consequences of deficiency include xerophthalmia: a condition associated which drying and thickening of the whitish part of the eye (conjunctiva) which result in the ulceration and destruction. In India, vitamin A deficiency is a very common cause of nutritional blindness. Furthermore, vitamin A deficiency can compromise the immune function apart from the delay in bone development.



Vitamin D

Vitamin D is also known as sunlight vitamin and the daily requirement of vitamin D in an average adult is 10 μg. It is richly found in animal fats such as eggs, butter, cheese, fish liver oils. Human skin can synthesize vitamin D by the action of the ultraviolet rays on the skin therefore, it is very important to expose our skin to sunlight at least 30 minutes a day. Vitamin D regulates calcium and phosphate metabolism by increasing their absorption from the stomach. It is also essential for stimulating the retention of calcium and phosphates by the kidneys that can eventually promote the calcification of bones and teeth to make them strong. Deficiency of vitamin D can lead to rickets, a very common condition in children. The impaired absorption and use of calcium and phosphate in adults lead to osteomalacia.



Vitamin E

Vitamin E  is a group of eight substances collectively called tocopherols. They are supplemented through nuts, egg yolk, wheat germ, whole cereals, milk and milk products such as butter. In general, vitamin E is an antioxidant as it protects our membrane lipids from being destroyed in oxidative reactions and they also aid in fighting coronary heart diseases. Recommended daily intake of vitamin E  is 10 mg for men and 8 mg for women. Thought the deficiency of vitamin E is rare, its deficiency can affect the WBCs which can eventually disturb our immune function. Some neurological abnormalities such as loss of balance, jerky movement of hands and legs, visual disturbances may occur if the deficiency is severe.



Vitamin K

It is very essential for blood clotting mechanism. The sources of vitamin K are liver, some vegetable oils and green leafy vegetables. It is synthesized in the large intestine by many microbes. The normal daily requirement of vitamin K is 1 μg/kg body weight. Our liver demands some proportion of vitamin K for the production of prothrombin and the coagulation factors VII, IX and X, which are much needed for the normal blood clotting mechanism. Deficiency of vitamin K means poor blood coagulation and excessive bleeding, therefore, it is very important to consume foods rich in vitamin K. Severe liver damage and the poor absorption by the intestine due to coeliac disease can also cause its deficiency. Newborn infants are injected vitamin K because their intestines don’t contain microbes that produce this vitamin.  



Water-soluble vitamins

Vitamin B complex

B complex is a group of water-soluble vitamins that promote enzyme activities that are involved in the chemical breakdown (catabolism) of nutrients to release energy. Vitamin B has several subunits as explained below.



Vitamin B1 (thiamin)

Vitamin B1 or thiamine is the most important vitamin among the B complex. It is richly found in nuts, yeast, egg yolk, liver, legumes, meat and the germ of cereals. An adult requires an average of 0.8 to 1 mg of B1 and the body can store a maximum of  30 mg. Thiamin is needed for the complete aerobic release of energy from carbohydrate. The deficiency can lead to the accumulation of tissue fluid (oedema) and heart failure. It is also essential for the normal functioning of the nervous system. Severe deficiency of Thiamin causes beriberi, which is mainly seen in countries where polished rice is the chief constituent of their daily diet. Beriberi patients can have severe muscle wasting, delayed growth in children, and degeneration of motor, sensory and some autonomic nerves. It also increases the risk of common infections and if untreated, death may result due to cardiac failure or severe microbial infection.



Vitamin B2 (riboflavin)

Riboflavin is found in yeast, green vegetables, milk, liver, eggs, and cheese.  our body needs 1.1 to 1.3 mg of riboflavin per day. It is easily destroyed by light and alkalis hence our body can store only little amounts of B2.  Deficiency may result in cracking of the skin at the angle of the mouth where the 2 lips join (angular stomatitis). It also causes inflammation of the tongue (glossitis) hence Doctors prescribe them often in those people who suffer from cracked tongue and lips.



Vitamin B3 (niacin)

Niacin is found in liver, cheese, yeast, whole cereals, eggs, fish and some nuts. Our body can also synthesize it with the help of amino acid tryptophan. It aids in releasing energy during the fat metabolism therefore it inhibits the deposition of the excess of cholesterol in our body. Deficiency occurs mainly in areas where maize is the chief constituent of their daily diet because the niacin found in the maize is in its unusable form. The daily requirement is 12 to 17 mg and it is fairly stable. The deficiency can lead to Pellagra which can become severe within 6 to 8 weeks of deficiency. Pellagra is characterized by redness of the skin in those parts exposed to sunlight. Some people feel  not feeling like to eat( or anorexia, nausea, difficult to swallow, inflammation of the oral mucosa, and some mental disturbances( dementia).



Vitamin B6 (pyridoxine)

This is found in egg yolk, beans, nuts like peas, soya beans, yeast, meat and liver. The daily requirement is about 1.2 to 1.4 mg for an adult. Dietary deficiency is rare, and it is associated with poor amino acid metabolism.



Vitamin B12 (cobalamin)

Vitamin B12 is also known as cyanacobalamin or simple cobalamin, which is  found in liver, meat, fermented liquors, eggs and milk. The usual daily requirement is 1.5 μg for an adult. It is essential for DNA synthesis. The deficiency results in a condition called megaloblastic anaemia, which is correctable with supplements. Cobalamin is also required for the formation and maintenance of myelin, the fatty substance that surrounds and protects some nerves. Deficiency can damage the nervous system resulting in the peripheral neuropathy which can be fatal sometimes.



Folic acid (folate)

Folic acid is richly found in liver, fresh leafy green vegetables and yeast. It is produced by bacteria present in the large intestine and its daily requirement is 200 μg. Like B12 , it is also essential for DNA synthesis. The deficiency can lead to impaired cell division during mitosis. Folate deficiency is much common during the pregnancy but it is reversible with folate supplements.



Pantothenic acid

It is primarily found in foods and is associated with amino acid metabolism. The recommended daily intake is 3 to 7 mg and no deficiency diseases have been identified.



Vitamin C (ascorbic acid)

It is one of the important vitamins found in fresh fruits like amla, oranges, grapefruit and lemons. The vitamin is readily soluble in water and is easily destroyed by heat, ageing, chopping, salting and drying. The deficiency can lead to scurvy where the limbs are bowed and weak. The daily requirement is 40 mg and after 2 to 3 months deficiency becomes apparent. It is associated with protein metabolism and it also acts as an antioxidant, protecting body molecules from damaging oxidative reactions. The deficiency is also manifested by bleeding through gums




Related reading


Proteins in our body                                  


Amino acids




Food preservation





  1. Classify vitamins. What are fat-soluble and water-soluble vitamins?

  2. What are vitamins ADEK called as?

  3. Explain the sources, deficiency disorders and the daily requirement of vitamin C

  4. List the scientific names of different vitamins

  5. What are the functions of vitamins in general?

  6. Which vitamin deficiency causes blindness?

  7. Which vitamin is required for proper growth and mineralization of bones

  8. What are antioxidants? Explain.




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