Short Notes For Vitamins
Vitamins: Functional aspects, Deficiency disorders, and their metabolism
The vitamins are natural and essential nutrients, required in small quantities, and play a major role in growth and development, repair and healing wounds, maintaining healthy bones and tissues, the proper functioning of an immune system, and other biological functions. These essential organic compounds have diverse biochemical functions.
There are different types of vitamins, and all are required for metabolic processes. The discovery of the vitamins was begun by Polish American biochemist Casimir Funk. Based on his research and discoveries on vitamins, their sources, functions, and deficiency disorders, he is considered the father of vitamins and vitamin therapy.
Like minerals, vitamins cannot be synthesized by our bodies. Therefore, we need to get them from the food we consume or in extreme cases supplements to keep ourselves healthy.
Types of Vitamins: Based on the solubility, Vitamins have been classified into two different groups:
- Fat-Soluble Vitamins.
- Water-Soluble Vitamins.
Fat-soluble vitamins: Fat-soluble vitamins are stored in the fat cells and as the name suggests, these vitamins require fat in order to be absorbed. Vitamin A, D, E and K are fat-soluble vitamins.
Effect of deficiency
Vitamin A (Retinol)
Formation of vision pigments, Differentiation of epithelial cells
Night-blindness, continued deficiency can lead to complete blindness.
Vitamin D (Cholecalciferol)
Increase the body’s ability to calcium and phosphorus, Transfer of calcium from blood to bones
Softening of bones called Rickets.
Vitamin E (Tocopherol)
Damage to skin and decrease in the rate of gamete production (sterility)
Vitamin K (Phylloquinone)
Formation of prothrombin (a key enzyme in blood clotting)
Delay in blood clotting
Few important points regarding fat-soluble vitamins:
- β-carotene (pro-vitamin A, abundantly present in carrot) and vitamin E are fat-soluble antioxidant molecules, which prevent ROS-mediated (reactive oxygen intermediates) cell or DNA damage and delay the aging process.
- Vitamin D exists in two possible forms i.e., vitamin D2 (ergocalciferol) and vitamin D3 (1,25-dihydroxycholecalciferol). Usually, the metabolic activity of both vitamin D2 and D3 are the same but, studies say that vitamin D3 is maintained at a higher level in serum for a greater duration than D2.
- Vitamin K is involved in the formation of coenzyme menaquinone, which is usually involved in the transfer of carboxyl groups or electrons in various reactions.
The best sources of fat-soluble vitamins include:
- Vitamin A: Found in potatoes, carrots, pumpkins, spinach, beef and eggs.
- Vitamin D: Found in fortified milk & other dairy products, Shark and fish liver oil and synthesized somewhat in the skin in the presence of sunlight.
- Vitamin E: Found in fortified cereals, leafy green vegetables, seeds, and nuts.
- Vitamin K: Found in dark green leafy vegetables and in turnip or beet green.
Water-soluble vitamins: Water-soluble vitamins are not stored in our body as their excess gets excrete through the urine. Therefore, these vitamins need to be replenished constantly. Most water-soluble vitamins are present in the form of coenzymes (organic cofactors of proteins/enzymes) in our body. Vitamin B complex and C are water-soluble vitamins.
Present as the coenzyme
The function of the coenzyme
Vitamin B1 (thiamine)
Thiamine pyrophosphate (TPP)
Vitamin B2 (riboflavin)
Flavin mononucleotide (FMN) and Flavin adenine dinucleotide (FAD)
Redox reactions involving proton (H+)
Vitamin B3 (niacin)
Nicotinamide adenine dinucleotide (NAD) and Nicotinamide adenine dinucleotide phosphate (NADP)
Redox reactions involving proton (H+)
Vitamin B5 (pantothenic acid)
Coenzyme A (CoA)
Carrier of the acyl group
Burning foot syndrome
Vitamin B6 (Pyridoxine)
Transfer of amino group
Vitamin B7 (biotin)
Hair loss, brittle nails
Vitamin B9 (folic acid)
Carrier of one carbon unit like formyl group
Vitamin B12 (cyanocobalamin)
Methylcobalamin or deoxyadenosylcobalamin
Vitamin C (ascorbic acid)
Few important points regarding water-soluble vitamins:
- Vitamin C is an antioxidant, as it is essential in healing injury and wound and for the formation of collagen, a protein found in fibrous connective tissues like tendons, ligaments, etc.
- Excess Vitamin B3 (Niacin) can cause liver injury.
- Transketolase is an enzyme of both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. The deficiency of Vitamin B1 (Thiamine) decreases the efficiency of the transketolase enzyme.
The best sources of water-soluble vitamins include:
- Vitamin B1 or Thiamine: Found in pork chops, ham, enriched grains, and seeds (especially rice).
- Vitamin B2 or Riboflavin: Found in whole grains, enriched grains, and dairy products.
- Vitamin B3 or Niacin: Found in mushrooms, fish, poultry, and whole grains.
- Vitamin B5 or Pantothenic Acid: Found in chicken, broccoli, legumes, and whole grains.
- Vitamin B6 or Pyridoxine: Found in fortified cereals and soy products.
- Vitamin B7 or Biotin: Found in many fruits like fruits and meats.
- Vitamin B9 or Folic Acid: Found in leafy vegetables.
- Vitamin B12 or Cyanocobalamin: Found in fish, poultry, meat, and dairy products.
- Vitamin C or ascorbic acid: Found in citrus fruits and juices, such as lemon, oranges, and grapefruits.
Vitamin metabolism: The liver is a major site for vitamin metabolism and vitamin storage. It produces bile for the absorption of fat-soluble vitamins (A, D, E, K). Larger quantities of fat-soluble vitamins than water-soluble ones can be stored in the body. Vitamins A, D, and K are stored chiefly in the liver; however, most of the stored vitamin E is found in body fat.
The water-soluble vitamins are absorbed in the intestine and are passed directly to the blood from which they are carried to the tissues in which they will be utilized. Vitamin B12 requires a substance known as an intrinsic factor in order to be absorbed. Water-soluble vitamins are generally excreted in the form of urine. Thiamin, riboflavin, vitamin B6, vitamin C, pantothenic acid, and biotin appear in the urine as free vitamins. Products (also called metabolites) that are formed during the metabolism of thiamin, niacin, and vitamin B6 also appear in the urine. The excretion of these vitamins is low when intake is sufficient for proper body function. If intake begins to exceed minimal requirements, excess vitamins are stored in the tissues and, as the tissues become saturated, the rate of excretion increases sharply. However, vitamin B12 is excreted solely in the feces.
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