Nutrition
VITAMINS - an overview for patients
Abstract
What are vitamins?
Vitamins are a group of organic compounds which are necessary for the normal development and functioning of the body.
They are only produced in small amounts by the body, and are mainly obtained through food.
They are only present in tiny amounts in food. The average adult eats about 600 grams of food per day, of which less than 1 gram is vitamins.
Eating a wide variety of foods is necessary for an adequate vitamin intake because no single food contains all the necessary vitamins.
Some foods, rich in vitamins, were used to cure diseases in ancient times such as the use of liver to treat night blindness (vitamin A deficiency) by the Egyptians, Chinese, Romans, Arabs and Greeks more than two thousand years ago.
Vitamin deficiencies were identified in the early 1900s, and now there is increasing scientific evidence that an inadequate vitamin profile is related to an increased risk of major chronic diseases.
Diet-related diseases continue to be a health problem in many African, Asian and Latin American countries. Marginal vitamin deficiencies are also common in many developed countries, but many people may not be aware they have a vitamin deficiency.
There are 13 known vitamins and each have different roles within the body.
Vitamin A
Vitamin A occurs in two principal forms in nature: retinol, which is found only in animal sources, and certain carotenoids, the best known of which is 'beta-carotene' found in carrots and other yellow to red plants. Beta-carotene can be converted to retinol in the body, and it may have a role in protecting against heart disease and cancer.
Vitamin A is essential for vision and adequate growth. Deficiency symptoms include night blindness, hyperkeratinosis of the skin, and xerophthalmia - an eye condition, which if untreated can lead to permanent blindness. Vitamin A deficiency is still widespread in many developing countries.
Vitamin A is found in pumpkins, kumara (sweet potato), apricots, squash, nectarines, peaches, and mangos. It is also found in spinach, broccoli, watercress, asparagus and peas.
The B Group Vitamins
The B group vitamins work as a team to convert food to energy. Vitamin B1 is vital for releasing energy from starchy and sugary foods, while vitamins B2, B6 and niacin help release energy from foods including protein and fats.
If you increase your energy intake, particularly by eating more carbohydrates, your body may need extra vitamin B.
Vitamin B12 and folic acid, together with iron and vitamin C are of major importance to sportsmen and women as they are used in the formation of red blood cells which transport oxygen to the muscles.
Vitamin B1 (thiamine)
Vitamin B1 is essential for the release of energy especially from carbohydrates, functioning of nerves, brain and muscles.
The best source of this is vitamin is from dried brewers yeast. Other good sources include pork, poultry, cereals, nuts and beans.
Vitamin B2 (riboflavin)
Vitamin B2 is found in all plant and animal cells. It is necessary for the release of energy from food and for healthy vision and skin.
Yeast and liver contain the highest amount of this vitamin. It is also found in other meat, eggs and dairy food.
Vitamin B6 (pyridoxine)
This vitamin is required for protein and fat metabolism, red blood cell formation, and the nervous system.
The best sources of this vitamin are liver of beef, pork and chicken. Other sources include cereals, fish, nuts, bananas and wheatgerm.
Vitamin B12 (cobalamin)
Vitamin B12 is necessary for the formation of red blood cells, a healthy nervous system, and is essential for growth.
This vitamin is stored efficiently by the body so a deficiency can take years to develop. Since it is found primarily in animal products, vegetarians are at risk from deficiency unless they take supplements. In its most extreme form, deficiency can lead to megaloblastic anaemia and irreversible degeneration of the spinal cord.
Vitamin E is found in animal meat, particularly liver, kidney, heart and brain. It is also present in yeast extract.
Biotin
This is needed for the manufacture of fatty acid and glycogen, protein metabolism and growth. It is found in egg yolk, liver, wholegrain cereals, and nuts.
Vitamin C (ascorbic acid)
Vitamin C is required for the production of collagen, the 'cement' substance that gives structure to muscles, vascular tissues, bones and cartilage. Deficiency causes a weakening of these tissues (scurvy), resulting in capillary bleeding.
Together with beta-carotene and vitamin E, vitamin C forms the trio of antioxidant vitamins now believed to help prevent degenerative diseases such as heart disease and cancer.
Vitamin C is also commonly used as a natural antioxidant, i.e. it is added to foodstuffs to protect colour, aroma or nutrient content, not for its action as a vitamin.
It is essential for the immune system and there is some evidence to show that extra vitamin C may reduce the severity of respiratory infections.
Vitamin C helps iron absorption. Its role in red blood cell formation also helps to transport essential oxygen to exercising muscles.
It promotes healthy body cells, blood vessels, bones and tissues (e.g. tendons and ligaments). It is also necessary for the manufacture of adrenaline.
Vitamin C is not stored within the body so make sure your diet contains a regular supply. It is found naturally in citrus fruits, blackcurrants, Brussels sprouts, strawberries, mango, sweet peppers, parsley, broccoli, kumara, and cauliflower.
Vitamin D
Vitamin D is required for the absorption of calcium and phosphorus from the diet, and is needed for healthy bone growth. It also plays an important role in the proper functioning of muscles, nerves, and blood clotting.
Vitamin D is produced by the action of sunlight on the skin. It is found in wholemilk, margarine, oily fish, and fortified cereals.
Vitamin E
Vitamin E is vital to the formation and normal function of red blood cells and muscles.
Vitamin E is a powerful antioxidant which helps to protect cells from damage by free radicals.
Polyunsaturated fats in our diets are protected from damage by vitamin E. Polyunsaturated fats, which are found in vegetable and fish oils, are essential for the normal function of cells in the body.
Together with beta-carotene and vitamin C , vitamin E forms the trio of antioxidant vitamins now believed to have a preventive effect on degenerative diseases such as heart disease or cancer.
The largest sources of vitamin E are vegetable oils including peanut, soya, palm, sunflower etc. Other sources include nuts, seeds, whole grains and leafy green vegetables.
Folic acid
Folic acid plays an important role in the metabolism of desoxyribonucleic acid (DNA) and ribonucleic acid (RNA), the carriers of genetic information in all living things. It is necessary for the formation of red blood cells and regulating growth cells.
Severe folic acid deficiency in humans results in megaloblastic anaemia. Folic acid reduces the risk of neural tube birth defects when consumed in adequate amounts by women before and during early pregnancy. For this reason, the enrichment of cereal products with folic acid is compulsory in the USA.
Folates are found in a wide variety of foods. The richest sources are liver, dark green leafy vegetables, beans, wheat germ and yeast. Other sources are egg yolk, fortified cereal, milk and dairy products.
Vitamin K
Vitamin K is needed primarily for the blood-clotting mechanism which prevents bleeding to death from cuts and wounds or internal bleeding.
The best plant sources of vitamin K are green leafy vegetables such as spinach, broccoli, cabbage and lettuce. Other sources include tomatoes, potatoes, oats, egg yolk, asparagus, butter and cheese.
Niacin
In the body, niacin is responsible for using the energy provided by food. Niacin is essential for growth and is involved in the production of hormones in the body.
Yeast, liver, poultry, lean meats, nuts and legumes contribute the largest amounts of niacin in food. Milk and green leafy vegetables contain smaller amounts.
Pantothenic acid
Pantothenic acid belongs to the group of B vitamins. It plays a key role in the maintenance and repair of all cells and tissues, the metabolism of fats and carbohydrate, and healthy skin and hair growth.
Pantothenic acid requires vitamin A, vitamin B6, vitamin B12, folic acid and biotin in order to function properly.
It is found in vegetables, liver, yeast extract, kidney, eggs, nuts and bread.