Vitamins

Introduction

Vitamins are essential micronutrients and play a very important role in our metabolism. They are required in very small amounts, but their deficiency causes certain diseases. Generally, vitamins are not synthesized in our bodies. Since they are mainly synthesized by plants and some of the vitamins required by human beings are synthesized in the gut of bacteria, they are obtained through food and considered as food factors. All vitamins are important and play an essential role in our balanced diet.

Vitamins are naturally occurring organic nutrients playing an important role in the growth and development of bones and tissues, repairing and healing wounds, and helping in maintaining the immune system of the human body.

Vitamins were discovered by the Polish American biochemist Casimir Funk in 1912. Presently, a total of 13 different vitamins have been seen in the metabolic processes.

Similar to vitamins, minerals are not synthesized by our body.

Vitamins are defined as organic compounds required in the diet in small amounts to perform specific biological functions for the normal maintenance of optimum growth and health of the organism. Vitamins are denoted by alphabets A, B, C, D, E, etc. Further sub-groups are designated as B1, B2, B6, B12, etc.

The term vitamin is derived from “Vitamine” which comes from the word vital + amine as earlier compounds had amino groups in them. Later on, it was revealed that most of them do not contain amino groups, so the letter ‘e’ was dropped and the term vitamin is used these days.

 Based on solubility, there are 2 types of vitamins. These are-

1. Fat-soluble vitamins
2. Water-soluble vitamins

The Fat-soluble vitamins

The fat-soluble vitamin groups are Vit. A, Vit. D, Vit. E and Vit. K. Vitamins related to this are soluble in fats and oils but are insoluble in water. These vitamins are stored in the liver and adipose tissues. 

Chemical properties of the fat-soluble vitamins

 Vitamins of this group are structurally related. They all have a five-carbon isoprene segment as their basic structural unit. All these vitamin groups contain many related compounds which show biological activity which is determined by chemical properties.

Vitamin A group

Carotenes, which are coloured molecules synthesized only in plants, have Vitamin A-like properties. The alpha and beta-carotenes and cryptoxanthin are important to humans. Retinol is considered the active form of vitamin A. It is involved in the visual process in the retina of the eye.

Vitamin D group

Ten compounds have vitamin D-like properties but ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) are the two most important compounds. Vitamin D3 represents a dietary source and vitamin D2 can be found in yeasts and fungi. Both of these can be formed from provitamin by UV irradiation.  In humans and other animals, vitamin D can be formed from provitamins found in the skin by sunlight.

Vitamin E group

This vitamin has several forms but active tocopherols i.e., alpha-tocopherol is the only one used by the human body. Its main role is as an antioxidant.

Vitamin K group

Vitamin K1 or phylloquinone is synthesized by plants and vitamin K2 or menaquinone is of microbial origin. Vitamin K2 is important for mammalian tissues.

Functions

Vitamin A – 

1. Maintains linings of the body surfaces (e.g.- skin, respiratory tract)
2. Helps in sperm formation
3. Maintain the functioning of the immune system.
4. Retinal in combination with a protein called opsin form a complex called rhodopsin which is involved in dark vision

Vitamin D– Required for bone growth or calcification.

Vitamin E– Necessary for normal growth of germ cells.

Vitamin K– 

1. Required for normal metabolism
2. Provides cellular energy to biological membranes
3. Necessary for clotting of blood

The Water-soluble Vitamins

The water-soluble vitamin groups include vitamin C (ascorbic acid) and vitamin B which include thiamin (vitamin B1), riboflavin (vitamin B2), vitamin B6, and niacin (nicotinic acid), vitamin B12, folic acid, pantothenic acid, and biotin. As the name indicates these vitamins are soluble in water, however, the degree of solubility is variable. Water-soluble proteins must be regularly supplied in our diet as they can be easily excreted through urine and hence are not stored in our body.

Chemical properties of the water-soluble proteins: The degree of solubility in water of these vitamins decides the route of absorption, excretion and degree of tissue storage of these vitamins.  Vitamins of this group contain elements like carbon, hydrogen, and oxygen and some also have nitrogen, sulfur, or cobalt. Water-soluble vitamins are inactive in their free state. For them to be functional they must be activated to their coenzyme form. The addition of the phosphate group activates thiamin, riboflavin, and vitamin B6 and the formation of a complex between free vitamins and other parts of the molecule activates niacin.

Functions of water-soluble proteins-

Vitamin B coenzymes function in enzyme systems that transfer certain groups between molecules. The pantothenic acid plays an important role in TCA cycle (tricarboxylic cycle, also called Kreb’s cycle or citric acid cycle) that interconnects carbohydrate, protein and fat metabolism.

Thiamin and vitamin B6 coenzymes convert the metabolic energy of carbohydrates and proteins during the TCA cycle. Niacin and riboflavin help in the transfer of H+ ions or electrons

Vitamin C functions as a strong reducing agent.

Sources of Vitamins

These organic compounds are abundantly found in both plant and animal sources and help in growth and development of the living organism.

Sources of fat-soluble proteins include

• Vit. A: potato, carrots, pumpkins, spinach, and eggs
• Vit. D: milk and other dairy products
• Vit. E: fortified cereals, leafy green vegetables, and nuts
• Vit. K: dark green leafy vegetables

Sources of water-soluble proteins include

• Vit. B1(Thiamin): grains and seeds

• Vit. B2 (Riboflavin): whole grains, and dairy products

• Vit. B3 (Niacin): mushrooms, fish, poultry, and whole grains

• Vit. B5 (Pantothenic Acid): chicken, broccoli, legumes and whole grains

• Vit. B6 (Pyridoxine): fortified cereals

• Vit. B7 (Biotin): fruits and meats

• Vit. B9 (Folic Acid): leafy vegetables

• Vit. B12: fish, poultry, meat and dairy products

• Vitamin C: citrus fruits like oranges and juices

Minerals

Like vitamins, minerals are also organic compounds naturally occurring in nature that help in the growth and development of the human body. Minerals are essential for the proper functioning of the human body. The deficiency of minerals may lead to certain disorders.

Here the table shows the lists of important minerals with their source and functions.

Conclusion

Vitamins are accessory food factors required in the diet. Vitamins are obtained from outside sources. This may include either plant or animal sources. Vitamins are naturally occurring organic compounds which help in growth and maintaining biological functions of the body. Vitamins are classified as fat-soluble vitamins (A, D, E and K) and water-soluble vitamins (B group and C). Excess of fat-soluble vitamins in the body may cause some biological complications as it is not water soluble whereas water soluble vitamins are not stored in the body and are excreted through urine. Similarly, minerals are also organic compounds and play an important role in proper functioning of the human body. Minerals like calcium help in bone growth and teeth development.