Nutritive value of vitamins

Vitamins are low molecular weight organic (carbon containing) compounds that are required in very small amounts for human growth, metabolism and health. Vitamins are essential nutrients. Vitamins cannot be bio-synthesized by the body but they must be ingested regularly through diet. The term “vitamine” was coined by Casimir Funk in 1912, meaning a basic essential for life. Generally vitamins and minerals are referred as vital body regulators because they are needed to make thousands of enzymes, hormones and other chemical messengers. Human beings need 13 vitamins and at least 10 minerals to stay healthy. Vitamins can be categorized into fat-soluble and water – soluble vitamins based on their solubility and polarity. Vitamins A, D, E and K (ADEK) are fat soluble and can be stored in fatty tissues and liver. The excess dietary intake could build up in the body and cause toxic effects. On the other hand vitamins B complex and C are soluble in water and harmless since there is little storage in the body.

Vital + Amines = Vitamin

Definition of vitamin

Vitamins are defined as “organic substances, needed in very small amounts that perform a specific metabolic function and must be provided in the diet of the animal.” They work as catalysts and substrates in metabolic reactions and some vitamins assist as co-factors for enzyme action.

Conditions of vitamin nutrition

Avitaminosis is a chronic or long-term vitamin deficiency e.g., night blindness(vitamin A),beri beri (vitamin B1), scurvy (vitamin C), rickets (vitamin D) and pellagra (vitamin B3).

Hypovitaminosis is caused by inadequate intake of one or more vitamins.

Hypervitaminosis results from excess intake of vitamins.

Antivitamins – a substance that destroys or inhibits the metabolic action of a vitamin e.g., avidin, sulphonamides.

Provitamins – a substance which the human body can convert into a vitamin e.g., beta carotene is a provitamin of vitamin A.  Dehydrocholesterol and ergosterol are provitamins of vitamin D.

Previtamins –a substance intermediate in the production of vitamins. A term synonym to provitamin.

Fat – soluble vitamins

Vitamin A

Vitamin A occurs in plants in the form of  provitamin carotene. The provitamin includes α -, β- and λ- carotenes and cryptoxanthin. The carotenes are the precursors of retinol. The modified forms of retinol are retinol (vitamin A aldehyde) and retinoic acid (vitamin A acid). Vitamin A is a 20-carbon compound with a β-ionone ring. The side chain is a highly unsaturated hydrocarbon unit. As many as 300 carotenoids have been identified in nature. The plant sources of β – carotenes include green leafy vegetables, carrot, red palm oil, and mango. The animal sources include fish liver oils (halibut, cod, and shark), milk, milk products and egg yolk. Avitaminosis results in the loss of night vision (nyctolopia). A failure of rod vision results in night blindness. The real sign of deficiency is xerophthalmia, dry keratinisation of cornea and conjunctiva. Vitamin A acts as an antioxidant (prevent cancer) as well as a hormone. It is essential for growth and differentiation of epithelial structure and bone. It promotes gluconeogenesis and synthesis of glycoproteins. The suggested daily dosage is about 700μg for adults and 300µg for children.

Vitamin D

Two forms of vitamin D are known. Cholecalciferol (D3) of animal origin is produced in the skin from a steroid previtamin7-dehydrocholesterol by sunlight (sunshine vitamin).  Calciferol (D2) is prepared synthetically by exposure of another provitamin ergosterol from yeast or plant sources. The two vitamins have the same activity in human beings. Ergosterol is obtained from plant sources like ergot and yeast. Dehydrocholesterol is obtained from animal sources like egg yolk, milk and fish liver oils. Vitamin D directly promotes the intestinal absorption of calcium and phosphorus. It facilitates calcification and development of bones. Vitamin D deficiency causes rickets in children and osteomalacia (a bone thinning disorder) and osteoporosis (reduced bone mineral density) in adults. The daily requirement of Vitamin D for children is estimated to be about 10μg (400 IU) and for adults is 5 µg (200 IU). The toxic symptoms of vitamin D Hypervitaminosis is loss of appetite, nausea, vomiting intense thirst and hypercalciuria (renal stone formation).

Vitamin E

Four forms of vitamin E are known such as α-, β-,λ- and ∆ - Tocopherol.  Chemically the compound is a 6- hydroxyl chroman with a phytyl side chain.  Vitamin E prevented sterility in human beings hence the name antisterility vitamin. The deficiency of vitamin E is shown to produce sterility, muscular dystrophy, haemolysis and megaloblastic anaemia. In infants vitamin E deficiency causes hemolytic anaemia.  Vitamin E is destroyed to great extent by cooking and food processing. The therapeutic daily dose is 500-1000 mg for the treatment of anaemia.  Dietary sources of vitamin E include leafy green and yellow vegetables, oils, grains, milk, meat and yeast. It plays an important role in maintaining stability and integrity of cell membranes. It has antioxidant properties and prevents free radical oxidation. It is relatively non-toxic.

Vitamin K

Vitamin E is a phytyl naphthoquinone occurring in the green leaves of most plants. There are two natural forms of this vitamin such as vitamin K1 (phylloquinone) and K2 (menaquinone). Vitamin K1 found in plants has a phytyl side chain and vitamin K2 produced by intestinal bacteria (microbial vitamin) has polyisoprenoid side chain. The dietary sources of vitamin K include green leafy vegetables, tomatoes, cauliflower, spinach, soybean oil, egg yolk and animal liver. Vitamin K is essential for normal blood clotting in wounds. Prothrombinogen and other blood clotting factors are formed in the liver with the help of vitamin K. The recommended daily allowance is 2 mg. The malabsorption of vitamin K results in the prolongation of clotting time and haemorrhages following an injury (hypoprothrombinemia).  Hypervitaminosis results in hyperbilirubinemia.

Water soluble vitamins

The B complex group of vitamins serve as coenzymes or coenzyme precursors. B vitamins are a group of eight water soluble vitamins. The B complex vitamins include thiamine (B1), riboflavin(B2), pantothenic acid(B3), niacin(B5), pyridoxine(B6), biotin (B7), folic acid(B9), cyanocobalamin(B12), inositol, choline, lipoic acid and para-aminobenzoic acid. B vitamins generally occur in protein –rich foods and dark green leafy vegetables. The B complex vitamins coexist in the same foods. The dietary requirement is between 10 – 400 mg of each daily. They help form red blood cells. Thiamine deficiency results in beriberi and riboflavin deficiency causes pellagra. The deficiency of pyridoxine causes anaemia and folic acid results in macrocytic anaemia. The B vitamins and vitamin C are often referred to as the “stress vitamins” because they are depleted by stress. B complex with Vitamin C plays a critical role in the body systems responsible for energy production, which helps to combat stress. The B vitamins are important for helping to reduce anxiety, depression, irritability, and nervousness. Most of the B vitamins, along with many other nutrients, are also removed when foods are highly refined or during the processing and cooking of foods.

Vitamin C

Vitamin C is also known as ascorbic acid or ascorbate and it exists in nature both as reduced or oxidised form called dehydroascorbic acid.  It can be destroyed by oxygen, alkalies and high temperature.  Recommended dietary allowance (RDA) for vitamin C is 90 mg/day for adult males and 75 mg/day for adult females. Vitamin C helps in the synthesis of collagen that holds muscles, bones, and other tissues together. Vitamin C also aids in wound healing, bone and tooth formation, strengthening blood vessel walls, improving immune system function, increasing absorption and utilization of iron, and acting as an antioxidant. It absorbs UV light and protects retina. The deficiency of vitamin C leads to scurvy, anemia, pains at the joints, hemorrhage from the mucous membranes of the mouth and GI tract.

Water-soluble vitamins are essential nutrients needed daily by the body in very small quantities. The B-complex vitamins can be found in a variety of foods like cereal grains and breads, as well as other foods such as meat, poultry, eggs, fish milk, legumes, and fresh vegetables. Vitamin C can be found in a many fruits and vegetables.

Vitamin therapy

Vitamins are essential organic substances usually supplied by foods. They are required by man in amounts ranging from micro-grams to milligrams per day. All the vitamins are essential for the normal growth, development and maintenance of the human body. They play an important role in the immune defense system. Vitamin therapy is a new and promising strategy for the treatment of certain chronic diseases. The therapeutically   new synthetic vitamin analogs with more potent, less toxic and long lasting effects are used in the treatment of cancers. However vitamins, vitamin analogs and vitamin mixture have been used and misused in the treatment of several diseases.