Role of vitamins in human body

Vitamins are organic substances, required in small amounts for body functioning and good health. They play an important role in the functioning of various processes inside the body such as metabolism, immunity, tissue growth and differentiation. Vitamins allow human body to grow and develop.

Once growth and differentiation are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs. They also allow human body to use efficiently the chemical energy provided by food, and to help process the proteins, carbohydrates, and fats of food.

Unlike carbohydrates, proteins and fats, vitamins do not provide calories. However, they help the body to use the energy from food.

Most vitamins cannot be made in human body. Only a few vitamins such as vitamin K and biotin are produced by the microorganisms present in the human intestine. Vitamin D is synthesized in the skin with the help of the natural ultraviolet wavelength of sunlight. Human body can produce some vitamins from precursors they consume.
Vitamins that cannot be synthesized by the human body, should be  acquired from food. Food is the best source of vitamins and minerals, and one may get vitamins by eating a healthy, balanced diet.

Vitamins are classified in two categories: water soluble and fat soluble. In humans, there are 13 vitamins: 4 fat-soluble (A, D, E, and K) and 9 water-soluble (8 B vitamins and vitamin C).

Fat soluble vitamins

Fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids (fats). Vitamins A, D, E and K are stored in significant amounts, in the liver. Because they are not water soluble, accumulate in the body and may lead to hypervitaminosis. So, Fat-soluble vitamin regulation is important in cystic fibrosis.

Vitamin A is needed for healthy vision, bone growth, reproduction and the immune system. It is manufactured in the body from substances called beta-carotenes, which are found in dark green, orange and yellow vegetables, such as spinach, carrots, broccoli, cantaloupe, mangos, apricots, vegetable soup and tomato juice, meat and dairy products such as liver, beef, chicken, whole milk and eggs.

Vitamin D, functions as hormone, regulators of mineral metabolism, or regulators of cell and tissue growth and differentiation. Vitamin D is present in body tissues and blood. Although vitamin D is obtained from foods, human body also produces it on exposure to sun. Consuming vitamin D rich foods and supplements requires fat sources, such as olive oil, salmon or nuts, because fat enhances its absorption.

Vitamin E protects red blood cells and is important in reproduction. It also acts as an antioxidant, preventing cell damage by ‘free radicals’ that are associated with aging and certain diseases. Vitamin E sources are vegetable oils, vegetables, cereals, wheat germ, whole-grain products, avocados and nuts.

Vitamin K is involved in blood clotting. Dark green, leafy vegetables, pork, liver and other meats are the main source in the diet. In addition, bacteria in the gut can make vitamin K, which is absorbed into the blood.

Water-soluble vitamins

Water-soluble vitamins dissolve easily in water and, are readily excreted from the body. Digestive system requires all essential vitamins. However, B vitamins and vitamin C play valuable roles in digestive health.

Vitamin B1, also called thiamine, helps the body to convert carbohydrates into energy during digestion.
Vitamin B3, or niacin, helps normal breakdown of carbohydrates, fats and alcohol.
Vitamin B6, or pyridoxine, promotes protein digestion.
Vitamin B, folate, or folic acid, is associated with reduced risk for colon cancer.
Vitamin B7 also known as biotin is responsible for the formation of fatty acids.
To meet B vitamin needs, eating a diet rich in whole grains, beans, seafood, dairy products and leafy green vegetables is required.

Vitamin deficiencies

Deficiencies of vitamins are classified as primary and secondary.
A primary deficiency occurs when an organism does not get enough of the vitamin in its food.
A secondary deficiency may be due to an underlying disorder that prevents the absorption or use of the vitamin, due to smoking, excessive alcohol consumption, or the use of medications that interfere with the absorption or use of the vitamin.
People who eat a varied diet are unlikely to develop a severe primary vitamin deficiency.
Well-known human vitamin deficiencies are,
thiamine -beriberi, niacin –pellagra, vitamin C-scurvy, and vitamin D- rickets.

Anti-vitamins are chemical compounds that inhibit the absorption or actions of vitamins. For example, avidin is a protein in egg whites that inhibits the absorption of biotin. Pyrithiamine is similar to thiamine, vitamin B1, and inhibits the enzymes that use thiamine.