what are vitamins

In developed countries, vitamin deficiencies result mainly from poverty, food fads, drugs, or alcoholism. Vitamin toxicity (hypervitaminosis) usually results from taking mega doses of Vit.A, D, B6, or niacin.

It may be fat soluble (A, D, E, and K) and water-soluble (B and C).

The B vitamins include biotin, folate, niacin, pantothenic acid, riboflavin, thiamine, pyridoxine, and B12.

Vegans may develop Vit.B12 deficiency unless they consume yeast extracts or Asian-style fermented foods. Strictly vegetarian diets also tend to be low in calcium, iron, and zinc.

what are vitamins
Vitamins – Structures, types and Functions

Vitamin Definition

Vitamin is a natural substance. It is found in foods and it helps to body development to make healthy.

According to Wikipedia,

A vitamin is an organic compound and a vital nutrient that an organism requires in limited amounts. An organic chemical compound (or related set of compounds) is called a Vitamin.

Types of Vitamins

VitaminChemical nameCommon nameFormula
Vitamin.ARetinal, Retinol, Four carotenoids, beta caroteneAntixerophthalmic factor (or) Bright eyes vitaminA1 (Retinol) – C20H30O


A2 (3-dehydroretinol) – C20H28O

Vitamin.DCholecalciferol, ErgocalciferolAntirachitic factor (or) Sunshine VitaminD2 (Ergocalciferol) – C28H44O


D3 (Cholecalciferol)- C27H44O

Vitamin.ETocotrienols, TocopherolsAntisterility factorα-Tocopherol – C29H50O2

β-Tocopherol – C28H48O2 ¥-Tocopherol – C28H48O2

Vitamin KMenaquinones, PhylloquinoneAntihemorrhagic factor (or) Coagulation vitaminK1- Phylloquinone – C31H46O2


K2-Farnoquinone – C41H56O2

Vitamin.B1Thiamine (or) AneurinAntiberiberi factor (or) Antineuritic factorC12H17ON4S
Vitamin.B2Riboflavin, LactoflavinYellow EnzymeC17H20O5N
Vitamin.B3Niacin, NiacinamidePellagra Preventive factor (or)

 Anti-Black Tongue factor



Vitamin B5Pantothenic acidFiltrate factor, Yeast factorC9H17O5N
Vitamin B6Pyridoxine, Pyridoxal, PyridoxamineAntidermatitis factorC8H11O3N  



Vitamin B7BiotinAnti-Egg white injury factor (or) Coenzyme RC10H16O3N2S
Vitamin B9Folinic acid, Folic acidLiver lactobacillus casei factorC19H19O6N7
Vitamin B12Hydroxocobalamin, Cyanocobalamin, MethylcobalaminAntipernecious anemia factorC3H88O14N14PCo
Vitamin CAscorbic acid (or)Antiscorbutic factor (or) CevitaminC6H8O6
Vitamin PFlavinoidsBiflavanoids 

These are two types. They are Water-soluble vitamins and Fat-soluble vitamins.

Water Soluble Vitamins

1. Biotin (Vit.B7)

Biotin (Vit.B7) acts as a co-enzyme for carboxylation reactions essential to fat and carbohydrate metabolism. Adequate intake for adults is 30 μg/day. The sources of Biotin are Liver, egg yolks, green vegetables. Whole grains are rich sources of biotin.

Biotin structure
Structure of Biotin

2. Folic Acid (Vit.B9)

Folate, also called Vit.B9, is involved in the maturation of red blood cells and the synthesis of purines and pyrimidines which are required for the development of the fetal nervous system. Adequate B9 intake before conception and throughout the first trimester of pregnancy helps prevent certain brain and spinal cord defects such as spina bifida. Folate is absorbed in the duodenum and upper jejunum.

The US recommended daily dose for folate is 400 μg and the upper limit is 1000 μg. Folate is essentially nontoxic. Deficiency produces megaloblastic anemia indistinguishable from that due to Cyanocobalamin (vVitB12) deficiency. A deficiency of folate in old age significantly increases the risk of developing dementia.

Folic acid foods: It is found in dried peas, dried beans, yeast, and leafy green vegetables such as spinach, endive, lettuce, and mustard greens.

Folic acid structure
Structure of Folic acid

3. Niacin (Vit.B3)

Niacin (Vit.B3 or nicotinic acid) derivatives include nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are coenzymes in oxidation-reduction reactions vital in cell metabolism.

Dietary niacin deficiency causes pellagra, a disease characterized by dermatitis, gastrointestinal disorders, and mental disturbances. Primary deficiency results from extremely inadequate intake of both niacin and the amino acid tryptophan, which usually occurs in areas where maize (Indian corn) constitutes a substantial part of the diet.

Mushrooms and fish are good sources of niacin.

Niacin structure
Structure of Niacin Molecule

4. Pantothenic Acid (Vit.B5)

Vit.B5 is widely distributed in foods, and high amounts are found in whole grain cereals, legumes, eggs, and meat. It is needed to form coenzyme-A (CoA) and is critical in the metabolism and synthesis of carbohydrates, proteins, and fats.

Adults require about 5 mg/day.

Food Sources: It is found in mushrooms, yeast, and liver.

Structure of Vitamin B5
Structure of Vitamin B5

5. Riboflavin (Vit.B2)

Riboflavin (Vitamin B2) is involved in carbohydrate metabolism as an essential coenzyme in many oxidation-reduction reactions. Riboflavin is essentially nontoxic. Riboflavin deficiency usually occurs with other B-Vitamin deficiencies.

Symptoms and signs include sore throat, lesions of the lips and mucosa of the mouth, glossitis, conjunctivitis, seborrheic dermatitis, and normochromic-normocytic anemia.

Riboflavin is found in mushrooms, yeast, and meats such as beef, pork, and lamb.

Structure of Riboflavin
Structure of Riboflavin

6. Thiamine (Vit.B1)

Thiamine (Vit.B1) is widely available in the diet. Thiamine is involved in carbohydrate, fat, amino acid, glucose, and alcohol metabolism. Thiamine is essentially nontoxic.

Thiamine deficiency (causing beriberi) is most common among people subsisting on highly refined rice or other carbohydrates in developing countries. Bean sprouts, brewer’s yeast, and fortified cereals are good sources of thiamine.

Structure of Thiamine
Structure of Thiamine

7. Cyanocobalamine (Vit.B12)

Cobalamin is a general term for compounds with biologic B12 activity. These compounds are involved in nucleic acid metabolism, methyl transfer, and myelin synthesis and repair. They are necessary for the formation of normal red blood cells.

It is released in the stomach’s acid environment and is bound to R protein. Pancreatic enzymes cleave the B12-R protein complex in the small intestine. After cleavage, intrinsic factor, secreted by parietal cells in the gastric mucosa, binds with the B12 vitamin.

Intrinsic factor is required for the absorption of B12, which takes place in the terminal ileum. The Recommended Dietary Allowance (RDA) is 2.4 micrograms, which is the amount found in 3 ounces (85 grams) of meat.

It is found in clams, oysters, turkey, chicken, beef, and pork. Dietary B12 deficiency usually results from inadequate absorption, but deficiency can develop in vegans who do not take vitamin supplements.

Deficiency causes megaloblastic anemia, damage to the white matter of the spinal cord and brain, and peripheral neuropathy which is characterized by tingling or numbness in the hands or feet.

8.Pyridoxine (Vit.B6)

Vitamin B6 includes a group of closely related compounds: pyridoxine, pyridoxal, and pyridoxamine.

The Vitamin B6 modified as pyridoxal phosphate by phopshorylation process and acts as a coenzyme in most of the important biochemical reaction like Blood, Skin and CNS.

It is a very important component in Heme biosynthesis, Nucleotide metabolism, Lipid metabolism, carbohydrate metabolism, and Amino acid metabolism. It is found in a variety of vegetables and meats.

Structure of Pyridoxine
Structure of Pyridoxine

Many breakfast bowls of cereal are fortified with Vitamin B6. Some natural sources of this vital amine are brewer’s yeast, Chinese cabbage (Pak Choi), and red and green peppers.

9. Ascorbic Acid (Vitamin C)

Vitamin C (ascorbic acid) plays a role in collagen, carnitine, hormone, and amino acid formation. It is essential for the healing of the wound and facilitates recovery from burns.

It is also an antioxidant, supports immune function, and facilitates the absorption of iron. In developed countries, deficiency can occur with general undernutrition, but severe deficiency (causing scurvy) is uncommon.

Structure of Vitamin C (Ascorbic Acid)
Structure of Vitamin C (Ascorbic Acid)

Symptoms of deficiency include fatigue, depression, and connective tissue defects such as gingivitis, rash, internal bleeding, or impaired wound healing. The Recommended Dietary Allowance (RDA) is 75 milligrams for women, 90 milligrams for men.

The tolerable upper intake level of Ascorbic acid is approximately 2 grams (2000 mg) per day. Higher amounts can cause stomach upset and diarrhea. It is found in fresh fruits and vegetables. Citrus fruits like oranges and lemons are good sources of Ascorbic acid.

Fat-Soluble Vitamins

1. Retinol (Vit. A)

Vitamin A (retinol) is required for the formation of rhodopsin, a photoreceptor pigment in the retina. It helps to maintain epithelial tissues. Normally, the liver stores 90% of the body’s Vitamin A.

The body releases retinol into circulation and it bounds with pre-albumin (transthyretin) and retinol-binding protein. β-carotene and other provitamin carotenoids, contained in green leafy and yellow vegetables and deep- or bright-colored fruits, are converted to Retinol.

Structure of Retinol
Structure of Retinol

Carotenoids are absorbed better from vegetables when they are cooked or homogenized and served with some fats or oils.

The Recommended Dietary Allowance (RDA) of Vitamin A is 900 micrograms for men, and 700 micrograms for women. Deficiency impairs immunity and causes skin rashes and typical ocular effects such as dry eyes and night blindness.

2. Vitamin D

Vitamin D has two main forms: D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D3 is synthesized in the skin by exposure to sunlight (ultraviolet radiation) and obtained in the diet chiefly in fish liver oils and egg yolks. In some developed countries, milk and other foods are fortified with vitamin D.

Human breast milk is low in vitamin D, containing an average of only 10% of the amount in fortified cow’s milk. Requirements for vitamin D increase with aging. Vitamin D is a prohormone with several active metabolites that act as hormones.

Structure of Vitamin D
Structure of Vitamin D

Vitamin D3 is metabolized by the liver to 25(OH)D, which is then converted by the kidneys to 1,25-(OH)2D (1,25-dihydroxycholecalciferol, calcitriol, or active vitamin D hormone).

25(OH)D, the major circulating form, has some metabolic activity, but 1,25(OH)2D is the most metabolically active. Inadequate exposure to sunlight may cause vitamin D deficiency.

Deficiency impairs bone mineralization, causing rickets in children and osteomalacia in adults and may contribute to osteoporosis.

Vitamin D metabolism
Vitamin D metabolism

The current recommendations from the Institute of Medicine are 200 IU/day from birth through age 50, 400 IU for those aged 51 to 70, and 600 IU for those over 70 years.

These recommendations were established by determining the level of Vitamin D that was enough to prevent bone demineralization or rickets. The safe tolerable upper intake level for Vitamin D is 10,000 IU/day.

Randomized trials using the currently recommended intakes of 400 IU of Vitamin D/day have shown no appreciable reduction in fracture risk. In contrast, trials using 700-800 IU Vitamin D/day found less fracture incidence.

Adults should be consuming at least 1000 IU per day of Vitamin D to maintain blood serum levels that are effective for strengthening the bones.

3. Tocopherol (Vit.E)

Tocopherol is a group of compounds (including tocopherols and tocotrienols) that have similar biologic activities. The most biologically active is α-tocopherol, but β-, γ-, and δ-tocopherols also have important biologic activity.

These compounds act as antioxidants, which prevent lipid peroxidation of polyunsaturated fatty acids in cellular membranes. Plasma tocopherol levels vary with the total plasma lipid levels. Normally, the plasma α-tocopherol level is 5 to 20 μg/mL. Dietary tocopherol deficiency is common in developing countries.


The deficiency causes degeneration of the axons of neurons (nerve cells) resulting in neurologic deficits, and fragility of red blood cells which is generally diagnosed as hemolytic anemia.

Taking Vitamin E supplements is not recommended because studies have found an increased risk of heart failure and general mortality.

It is found in spinach, watercress, mustard greens, and many green vegetables. Good sources of Vitamin E are oily plant seeds such as peanuts and sunflower kernels.

4. PhylloQuinone (Vit. K)

Vitamin K1 (phylloquinone) is dietary vitamin K. Dietary fat enhances its absorption. Infant formulas contain supplemental vitamin K.

Vitamin K2 refers to a group of compounds (menaquinones) synthesized by bacteria in the intestinal tract; the amount synthesized does not satisfy the vitamin K requirement.

Structure of Vitamin K1
Structure of Vitamin K1

The Recommended Dietary Allowance (RDA) is 120 micrograms for men, and 90 micrograms for women. It controls the formation of coagulation factors II (prothrombin), VII, IX, and X in the liver.

In healthy adults, dietary vitamin K deficiency is uncommon because vitamin K is widely distributed in green vegetables such as kale, spinach, and mustard greens. The bacteria of the normal gut also synthesize menaquinones.