Vitamins : Classification, Functions and Deficiency Symptoms

The word ‘vitamin’ (Latin, vita, life+ amine) is derived from the original word “vitamine”, coined by Casimir Funk in 1912. Vitamin is an organic compound which is found in the food in variable and minute quantity and must be supplied to the animal organism from the external sources. It is a vital nutrient for an organism which maintains the normal body growth and other functions. It keeps your nerve healthy, gets energy by the body from food and helps blood to clot properly. 

There are 13 vitamins which are required for human metabolism. They are:

Serial NoVitaminsAlternative namesNature


Vitamin A

Retinol and Carotinoids



Vitamin B1




Vitamin B2




Vitamin B3




Vitamin B5

Pantothenic acid



Vitamin B6




Vitamin B7




Vitamin B9

Folic acid or Folate



Vitamin B12




Vitamin C

Ascorbic Acid



Vitamin D




Vitamin E

Tocopherols and tocotrienols



Vitamin K



Classification of Vitamins

According to the property of solubility, vitamins are mainly divided into two groups:

1. Fat-soluble vitamins: If vitamins are soluble in a fat solvent such as ether, chloroform, benzene, carbon, tetrachloride etc, then they are known as fat-soluble vitamins. Vitamin A, D, E and K are fat soluble.

2. Water-soluble vitamins: Vitamin B-complex and vitamin C are water-soluble vitamins because they are soluble in water.

Fat-soluble Vitamins

Vitamin A

It is also known as Retinol and carotenoids. It is an unsaturated long chain alcohol C20H29OH. It is colorless oil, soluble in fat but insoluble in water. It is heat-stable.

Vitamin A Sources: It is found in cod liver oil, halibut liver oil, milk, butter, eggs, fishes, Meat, Carrots, spinach, mango, tomatoes, Dark-colored fruit, and dairy products such as cheese, yogurt, butter, and cream.

Functions of Vitamin A
  • It controls bone growth;
  • It prevents infection;
  • It is a component of rhodopsin(eye), essential for night vision;
  • It maintains the health and activity epithelial tissue as and glands;
  • It maintains the integrity of nerves tissue and epithelial tissue;
  • It helps reproduction and embryonic development;
Deficiency Symptoms of Vitamin A
  • Night blindness;
  • Xerophthalmia;
  • Keratinisation of epithelial tissue;
  • Skeletal growth retardation;
  • Susceptibility of infection;
  • Nervous debility;
  • Dry skin, diarrhea;

Daily Requirement of Vitamin A: 5000 IU in adult and 6000-8000 IU in children;

Vitamin D

It is also known as Calciferols. It is an oily compound soluble in the fat solvent but insoluble in water. It is heat-stable. There are groups of vitamin D of which D2 (ergocalciferol) and D3 (cholecalciferol) are chiefs.

Vitamin D Sources: Animal sources are the only sources of vitamin D. It is found in liver, Fish such as salmon, mackerel, herring etc, fish liver oil (cod and halibut), eggs, meat, milk, butter, and dairy products such as cheese, yogurt, butter, and cream.

Functions of Vitamin D
  • It helps in the bone formation by direct action on the bone cell;
  • It helps the absorption of calcium and phosphorous from intestine;
  • It helps in proper mineralization of bones;
Deficiency Symptoms of Vitamin D
  • Abnormal bone growth in children;
  • Osteomalacia in adults
  • Tetany in children;
  • Mal-development of teeth various bony deformities;
  • Retardation of bone growth;

Daily Requirement of Vitamin D: 400 IU (10 µg)

Vitamin E

It is also known as Tocopherols and tocotrienols. It is yellow colored oily substance, soluble in fat solvents but insoluble in water. It is heat stable and antioxidants that help to prevent various diseases.

Vitamin E Sources: Fish such as sardines, Egg, egg yolk, milk, butter, Seeds and nuts, Papaya and mango, Wheat germ, wheat germ oil, sunflower oil, spinach,  lettuce, broccoli, alfa-alfa, asparagus, turnip greens etc.

Functions of Vitamin E
  • It has a strong antioxidant property which prevents unwanted oxidation in the body;
  • It participates in cellular electron transport system;
  • It helps to prevent sterility;
  • It is essential for embryonic development;
  • It is required for normal functions of muscles;
  • It helps in the formation of the cell membrane;
Deficiency Symptoms of Vitamin E
  • Muscular dystrophy;
  • Habitual abortions;
  • Atrophy of germinal epithelial of genital organs;
  • Peripheral neuropathy;
  • Breakdown of RBC (red blood cells);

Daily Requirement of Vitamin E: 22.4 IU

Vitamin K

Vitamin K is also known as the “blood-clotting vitamin or Quinones.  It is a yellow oily substance, soluble in fat soluble but insoluble in water. It is heat-stable vitamin which plays an important role in bone health.

Vitamin K Sources: Cauliflower, Cabbage, Cereals, spinach, broccoli, romaine lettuce, Brussels sprouts, asparagus, Legumes, Beets, Wheat germ, Peanut butter,  Fish, liver, beef, eggs, Egg yolk, kidney, Milk, Pork, Yeast, Nuts. Chocolate etc.

Functions of Vitamin K
  • It helps in the synthesis of proteins (prothrombin) involved in blood coagulation and bone metabolism;
  • It helps in the phosphorylation process;
Deficiency Symptoms of Vitamin K
  • Defective blood coagulation;
  • Internal bleeding;

Daily Requirement of Vitamin K: A dose of Vitamin K varies depending on several factors such as age, gender, weight, etc. The daily recommended dose is typically 70 to 90 micrograms for adults;

Water Soluble Vitamins

Vitamin B1

It is also known as Thiamine and is a white crystalline substance, soluble in water and heat-stable. It enables the body to use carbohydrates as energy. It plays an important role in heart, nerve and muscle function. It is also essential for the metabolism of glucose.

Vitamin B1 Sources: Brown rice, Cereal grains, sunflower seeds, whole-grain rye, asparagus, kale, cauliflower, Legumes (dried beans), Peas, beans, nuts, yeast, potatoes, oranges, Dried milk, liver, beef,  eggs, egg yolk, pork, etc.

Functions of Vitamin B1
  • It acts as a coenzyme in carbohydrate metabolism;
  • It helps in the oxidation of sugar in the tissue and brain;
  • It is concerned in the neuromuscular transmission of impulse;
  • It plays an important role in heart, nerve and muscle function;
Deficiency Symptoms of Vitamin B1
  • Beriberi;
  • Wernicke-Korsakoff syndrome;
  • Short-term memory loss;
  • Weight loss and anorexia;
  • Heart becomes enlarge

Daily Requirement of Vitamin B1: 1.1-1.2 mg

Vitamin B2

It is also known as Riboflavin, is a yellowish crystalline solid substance and soluble in water. It is heat-stable. It is involved in the release of energy in the electron transport system. It helps the production of RBC (red blood cells)  and is important for body growth.

Vitamin B2 Sources: Green beans, asparagus, bananas, peas, persimmons, okra, chard, cottage cheese, milk, yogurt, meat, eggs, egg albumin, fish, liver etc.

Functions of Vitamin B2
  •  It helps in the maintenance of epithelial and mucosal integrity;
  • It is essential for growth;
  • It acts as cofactors which are essential for flavoprotein enzyme reactions;
Deficiency Symptoms of Vitamin B2
  • Loss of appetite;
  • Gastrointestinal symptoms;
  • Angular stomatitis (oral fissures at corners of the mouth);
  • Glossitis (lesion of the tongue);
  • Cheilosis (lesion of the lips);
  • Vascularization of the cornea;
  • The defect of eye vision;

Daily Requirement of Vitamin B2: 1.1 -1.3 mg

Vitamin B3

It is also known as niacin, is a white crystalline and soluble in water. It helps to maintain different bodily functions. It also converts fats to energy and syntheses cholesterol.

Vitamin B3 Sources: Nuts, Eggs, Potato, Pea, Tomato, Avocado, wheat, Legumes, broccoli, carrots Meat, Fish (such as tuna and salt-water fish), liver, kidney, heart, chicken, beef, bread, cereals, whole grains, mushrooms, and brewer’s yeast etc

Functions of Vitamin B3
  • It is a prosthetic group in the coenzyme A;
  • It helps in the formation of hemoglobin;
  • It helps in amino acid and fatty acid metabolism;
Deficiency Symptoms of Vitamin B3
  • Pellagra;
  • Adrenal insufficiency;
  • Degeneration of the spinal cord;
  • Alopecia;
  • Dermatitis;

Daily Requirement of Vitamin B3: 14-16 mg

Vitamin B5

It is also known as pantothenic acid, is a solid crystalline substance. It is water soluble and acts as a precursor of coenzyme A. It is an essential element which is needed to metabolize many molecules.

Vitamin B5 Sources: Whole-grain cereals, broccoli, avocados, royal jelly,  fish ovaries, meats, Milk, Eggs, Mushroom, sweet potatoes, kale, and other vegetables in the cabbage

Functions of Vitamin B5
  • It has a role in metabolism;
  • It needs to synthesize cholesterol;
  • It is essential for growth;
  • It properly helps in the nervous system;
  • It helps in the breakdown of fats and carbohydrates to produce energy;
Deficiency Symptoms of Vitamin B5
  • Paresthesia;
  • Fatigue;
  • Depression;
  • Irritability;
  • Insomnia;
  • Vomiting;
  • Stomach pains;

Daily Requirement of Vitamin B5: 5 mg

Vitamin B6

It is also known as Pyridoxine. It is white crystal and soluble in water. It is heat-stable. It helps to create RBC (red blood cells) and releases sugar from stored carbohydrate to get energy.

Vitamin B6 Sources: Liver, egg yolk, yeast, kidney, Meats, bananas, dried beans, Peas, soybeans, cereals, vegetables, and nuts, Avocado.

Functions of Vitamin B6
  • It helps in some unsaturated fatty acids amino acids metabolism;
  • It acts as a coenzyme for transaminases, decarboxylases, and deaminases etc;
  • It helps in the synthesis of fat from proteins and carbohydrates;
  • It helps to create RBC (red blood cells);
  • It helps to releases sugar from stored carbohydrate to get energy;
Deficiency Symptoms of Vitamin B6
  • Dermatitis;
  • Anemia;
  • Peripheral neuropathy;
  • Retardation in body growth;
  • Convulsion and hyperirritability in infants etc;

Daily Requirement of Vitamin B6: 1.5 mg

Vitamin B7

It is also known as Biotin. It is water soluble, an essential vitamin which plays an important role in maintaining a healthy metabolism of fatty acids, glucose, and amino acids.

Vitamin B7 Sources: Egg yolks, liver, tomatoes, nuts, soybeans, whole grains, yeast, peanuts, leafy green vegetables etc.

Functions of Vitamin B7
  •  It helps to treat skin disorders;
  • It improves the metabolism of the body;
  • It boosts up healthy hair;
Deficiency Symptoms of Vitamin B6
  • Dermatitis;
  • Enteritis or inflammation of the intestine;
  • Skin disorder;

Daily Requirement of Vitamin B7: 30 µg

Vitamin B9

It is also known as Folic acid or folate. It is a yellowish water-soluble vitamin. It is a very essential element which helps to prevent anemia, abnormal brain growth, and skin disorder etc.

Vitamin B9 Sources: Leafy vegetables, bread, cereal,  pasta, liver, legumes, liver, fish, kidney, baker’s yeast, whole grain products, different types of fruits,  sunflower seeds etc.

Functions of Vitamin B9
  • It takes part in the formation and maturation of RBC(Red blood cells);It acts as a coenzyme;
  • It helps in the synthesis of DNA in the nucleus of the cell;
  • It prevents coronary heart diseases;
  • It helps to prevent abnormal brain growth;
  • It helps against anemia, indigestion and skin disorder;
  • It is essential for proper cell division;
Deficiency Symptoms of Vitamin B9
  • Anemia;
  • Abnormal brain growth;
  • Skin disorder;
  • Coronary heart diseases;
  • Birth defects;

Daily Requirement of Vitamin B9: 400 µg

Vitamin B12

It is also known as cyanocobalamin. It is reddish crystalline solid substance and soluble in water. It contains cobalt.

Vitamin B12 Sources: Fish, shellfish, milk, liver, kidney, meat, eggs, cereals, soy products, yeast etc

Functions of Vitamin B12
  • It reduces symptoms and side effects of anemia;
  • It helps to prevent liver disorder, kidney disorder, and mouth ulcers;
  • It defends against heart stroke;
  • It regulates nerve cells;
  • It helps in the replication of DNA;
  • It has a role in amino acid synthesis;
  • It helps in the formation of RBC;
  • It has a role in nucleoprotein metabolism;
Deficiency Symptoms of Vitamin B12
  • Anemia;
  • Liver disorder;
  • Kidney failure;
  • Ulcers in the mouth;
  • List Element

Daily Requirement of Vitamin B12: 2.4 µg

Vitamin C

It is also known as Ascorbic acid. It is a derivative of the hexose L-glucose. It is colorless crystalline solid substance and soluble in water. It is destroyed in heat also when exposed in air.

Vitamin C Sources: Broccoli, spinach; Cauliflower, Potatoes, Cabbage, Citrus fruits(lemon, orange), Apple, Tomatoes, Strawberries, mangoes etc.

Functions of Vitamin C
  • It regulates oxidation  and acts as a hydrogen carrier inside the cell;It maintains the integrity of colloidal intercellular substances;
  • It helps in the formation of RBC;
  •  It helps in the development of matrix and deposition of calcium and phosphorous in the bones;
  • It plays an important role in wound repair;
  • It controls the metabolism of tyrosine and phenylalanine;
  • It is the powerful and essential antioxidant in the body;
Deficiency Symptoms of Vitamin C
  • Scurvy;
  • Eye disorder;
  • Common cold;
  • Diabetes;
  • Heart diseases;
  • High blood pressure;
  • Kidney disorder;
  • Destroy the immune system;

Daily Requirement of Vitamin C: 80-90 mg