Introduction to Vitamins, thei...

    Vitamins are organic molecules that are essential for the proper functioning of the body. They are required in small amounts for the maintenance of good health, but they cannot be synthesized by the body (except Vitamin D, K, and some of the vitamins of B-Complex ), and therefore must be obtained from the diet or supplements.

    Vitamins play a variety of roles in the body, including helping to build and maintain healthy tissues, supporting the immune system, and converting food into energy. A deficiency in certain vitamins can lead to specific deficiencies or health problems.

Vitamins, their classes, sources, and roles in our body.

Classification of Vitamins

    There are two main types of vitamins: fat-soluble vitamins and water-soluble vitamins.

A. Fat-soluble vitamins: These vitamins are dissolved in fats and stored in the body's fatty tissue. Examples include vitamin A, vitamin D, vitamin E, and vitamin K.

B. Water-soluble vitamins: These vitamins dissolve in water and are not stored in the body to the same extent as fat-soluble vitamins. Examples include vitamin C and the B-complex (B1 to B12). 

A. Fat Soluble Vitamins

• They include vitamins A, D, E, and K.
• Only Vitamin K has a coenzyme activity.
• These vitamins are released, absorbed, and transported along with the diet's fat.
• They are not readily excreted in the urine.
• They are stored in significant amounts in the liver and adipose tissues.

Vitamin-A (Retinol)

Vitamin A is present in the diet in the following two forms

a. Preformed vitamin A (retinol): It is found in animal-derived foods such as liver, eggs, and dairy products,  and 

b. Provitamin A (beta-carotene): It is found in plant-derived foods such as fruits, vegetables, and whole grains

Functions of Vitamin-A

    Before getting depth into the Functions of Vitamin-A, when have to first consider two forms of Vitamin-A i.e. 

a. Retinal: It is the aldehyde form of Retinol that performs all Vitamin-A's functions.

b. Retinoic Acid: It is an oxidized form of retinol that performs the functions of growth and maintenance of epithelial tissues.

    Now we are going to explore the functions/roles of Vitamin-A, given as under

1. Role of Vitamin-A in Visual Cycle  

The visual cycle is the process by which the body converts light into electrical signals that can be interpreted by the brain.

• In the visual cycle, vitamin A is converted into a retinal molecule, a key component of the protein rhodopsin. 
• Rhodopsin is found in the rods, which are light-sensitive cells in the retina that are responsible for detecting low levels of light (dim light). 
• When eyes are exposed to bright light all of the rhodopsin gets hydrolyzed and when the person comes back to the darkroom, he/she will be unable to see in the darkroom for a while.
• In the darkroom or dim light, re-synthesis of rhodopsin takes place and after some time the person begins to see in the dim light. 
• If Vitamin-A is deficient, the synthesis of rhodopsin cannot take place and the person becomes unable to see in dim light, a condition known as Night Blindness.     

2. Role of Vitamin-A in Reproduction

    Vitamin A is also important for the proper functioning of the reproductive system.

• In males, vitamin A is required for the production of testosterone, a male hormone that is important for the development and maintenance of male reproductive organs. Vitamin A is also involved in the production of sperm and may be important for fertility.
• In females, vitamin A is required for the proper functioning of the ovaries and the development and maintenance of the female reproductive system. It is also involved in the production of estrogen and progesterone, two hormones that are important for reproductive health.
• Vitamin A is essential for the proper functioning of the reproductive system, and a deficiency in vitamin A can lead to reproductive problems such as infertility.

3. Role of Vitamin-A in Bones growth

Vitamin A is also important for the proper growth and development of bones.

• Vitamin A is involved in the synthesis of collagen, a protein that is important for the structure and strength of bones. It is also involved in the regulation of osteoclast activity, which are cells that break down bone tissue.
• In addition, vitamin A plays a role in the development and maintenance of the chondrocytes, which are cells that produce and maintain cartilage. Cartilage is a type of connective tissue that cushions and supports bones and joints.
• Vitamin A is essential for the proper growth and development of bones, and a deficiency in vitamin A can lead to bone problems such as osteoporosis.

4. Metabolic Role of Vitamin-A

    Vitamin A is also involved in various metabolic processes.

• One of the main metabolic roles of vitamin A is in the maintenance of the epithelial tissues, which are tissues that form the outer layers of the skin, the respiratory and digestive tracts, and other organs. Vitamin A is required for the proper differentiation and proliferation of these cells, and it helps to maintain their integrity and function.
• Vitamin A has also involved in the metabolism of fats and the synthesis of certain hormones e.g. glucocorticoids. 
• It is required for the proper functioning of the liver, which plays a central role in metabolism, and it is involved in the synthesis of bile, which is necessary for the digestion and absorption of fats.
• It also helps in the synthesis of glycogen from its precursor, such as lactate and glycerol (gluco-neo-genesis).
• It is required for the normal activity of mitochondria. An excess or deficiency of Vitamin-A interferes with Oxidative Phosphorylation (ATP Production).

5. Role of Vitamin-A in the prevention of Chronic Diseases

    Some studies have suggested that vitamin A may also have a role in the prevention of chronic diseases.

• One area where vitamin A may have a protective effect is the development of cancer. Some studies have suggested that vitamin A may help to prevent the development of certain types of cancer, such as lung, breast, and prostate cancer. However, more research is needed to confirm these findings and to determine the optimal dosage and duration of vitamin A supplementation for cancer prevention.
• Vitamin A may also have a protective effect against cardiovascular disease. Some studies have suggested that high levels of vitamin A may be associated with a lower risk of heart disease, although more research is needed to confirm these findings.