vitamins for the body

8/6/2019 Vitamins for the body

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VITAMINSSuperfitnessexpert.com

What are vitamins?

Vitamins are molecules required by the body in small amounts for a variety of essential processes in

the body. They are classified as micro nutrients because they are normally required in small

amounts: usually a few milligrams (mg) or micrograms (g) per day. Most vitamins cannot be

synthesised by the body so must be obtained by the diet. An exception is vitamin D which can be

synthesised by the action of sunlight on the skin. Small amounts of niacin (a B vitamin) can be

made from the amino acid, tryptophan.

Vitamins have a diverse range of functions in the

body, including:

Co-factors in enzyme activity

Antioxidants (prevent damage from freeradicals)

Pro-hormone (only vitamin D)

If insufficient amounts of vitamins are

available to the body because of a poor

diet or some medical condition, such as

malabsorption disorders or inborn errors

of metabolism, a deficiency disease can

develop. Vitamin deficiency diseases are

rare in the UK but still occur in some

parts of the world.

Vitamins have been grouped into two categories: fat soluble vitamins and water soluble vitamins.

Originally vitamins were given letters (A, B, C etc.) but are now more commonly referred to by

their names, e.g. fol ate, riboflavin.

Fat soluble vitamins

Vitamin AVitamin A can be obtained in 2 forms

1. preformed retinol (retinyl esters) found in animal derived foods

2.carotenoids which are mainly plant derived (beta carotene being the most abundantcarotenoid), some of which can be converted to retinol in the body; 6mg of beta

carotene is equivalent to 1mg of retinol.
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The total vitamin A content of the diet (from both animal and plant sources) is normally expressed

as retinol equivalents (RE).

Vitamin A is essential to the normal structure and function of the skin and mucous membranes such

as in the eyes, lungs and digestive system. Therefore, it is vital for vision, embryonic development,

growth and cellular differentiation, and the immune system.

DeficiencyVitamin A deficiency is a serious public health problem worldwide,. It can lead to night blindness

(impaired adaptation to low-intensity light) and an eye condition called xerophthalmia (dryness of

the conjunctiva and cornea) and eventually total blindness. Marginal deficiency contributes to

childhood susceptibility to infection, and therefore morbidity and mortality, in both developing and

developed countries. Vitamin A deficiency is common in many developing countries especially

among young children.

Food sources

Liver, whole milk, cheese, butter, margarine and

many reduced fat spreads are dietary sources of

retinol. Carrots, dark green leafy vegetables and

orange-coloured fruits, e.g. mangoes and

apricots are dietary sources of carotenoids.

Vitamin DDietary vitamin D exists as either ergocalciferol (vitamin D2) or cholecalciferol (vitamin D3).

Ergocalciferol (D2) is derived from the UV irradiation of the plant sterol ergosterol, which is widely

distributed in plants and fungi. (D3 ) is formed from the action of UV irradiation on 7-

dehydrocholesterol in the skin of animals including humans.

Vitamin D is not classically a vitamin but a pro-hormone, acting as a precursor to one of thehormones involved in calcium homoeostasis. Cholecalciferol is metabolised to the active steroid

hormone 1,25-dihydroxyvitamin D3 in the liver and kidney. In this form it works as a hormone

regulating the amount of calcium absorbed in the intestine. It is also essential for the absorption of

phosphorus and for normal bone mineralisation. Vitamin D is also involved in the regulation of cell

proliferation and differentiation. Vitamin D is also an activator of insulin-like growth factor (IGF-1)

and, associated with this, poor vitamin D status is linked to sarcopenia (age related loss of skeletal

muscle) which affects up to 25% of those over the age of 65 years and more than half of those over

Deficiency

Deficiency of vitamin D results in poor calcification of the skeleton and hence skeletal deformity inchildren (rickets) and it leads to pain and bone fragility in adults (osteomalacia).


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Sources

Oily fish, eggs, fortified cereals and margarine

are the main dietary sources of vitamin D. In the

UK, the law states that margarine must be

fortified with vitamin D (and vitamin A).

Vitamin D is also often voluntarily added toreduced fat spreads, as is vitamin A. Human

milk contains low levels of vitamin D, but infant

formula is fortified with 0.001-0.0025

mg/100kcal.

Vitamin EVitamin E is a group of eight lipid-soluble compounds synthesised by plants, tocopherols and

tocotrienols. Alpha-tocopherol accounts for 90% of the vitamin E in human tissues. Vitamin E acts

as an antioxidant and is required to protect cells against oxidative damage from free radicals, for

example oxidation of the lipids in cell membranes. Vitamin E content in food is expressed in terms

of mg equivalents based on the biological activities of the tocopherols present

Deficiency

Existence of dietary vitamin E deficiency is not considered to be a problem even in people

consuming a relatively poor diet. Deficiency only occurs in people with severe fat malabsorbtion

and rare genetic disorders.

Food sources

Foods containing large amount of polyunsaturated fatty acids will generally contain large amounts

of vitamin E, therefore the richest sources of vitamin E are vegetable oils, nuts and seeds. Since

vegetable oils are the richest source, deficiency is rare.

Vitamin K

Vitamin K is required for the synthesis of several of proteins required for normal blood clotting and

bone structure. Vitamin K is synthesised by bacteria in the large bowel and is also present in both

plant and animal foods.

Deficiency

Deficiency is rare as vitamin K is widely available from the diet and is also provided by gut

bacteria.


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Food sources

Dietary vitamin K is obtained from green leafy

vegetables, dairy products and meat.

Water soluble vitamins

Thiamine (vitamin B1)

Thiamine is a co-enzyme for several central energy-yielding metabolic pathways, and therefore is

required to release energy from carbohydrate. As a result thiamine requirement is related to the

amount of energy consumed. Thiamine is also involved in the normal function of the nervous

system and other excitable tissues, such as skeletal muscles and the heart.

Deficiency

Deficiency of thiamine causes the peripheral nervous system disease bier-beri. This became a public

health issue in the Far East in the nineteenth century with the introduction of highly milled

(polished) rice. While beriberi is now rare, it remains a problem in some parts of the world where

rice is the staple food. A different condition due to thiamine deficiency, affecting the central nervous

system rather than the peripheral is sometimes seen in alcoholics and people with HIV, known as

Wernicke-Korsakoff syndrome. This is caused by a combination of low intake and impairment of

absorption and utilisation of the vitamin.

Food sources

Whole grains, nuts, meat (especially pork), fruit

and vegetables and fortified breakfast cereals are

sources of thiamine in the diet. In the UK, white

and brown bread flour are fortified with

thiamine by law (and also with calcium andiron).


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Riboflavin (vitamin B2)

Riboflavin functions as a co enzyme in a wide variety of reactions that take place in the body.Riboflavin is required to release energy from protein, carbohydrate and fat. It is also involved in the

transport and metabolism of iron in the body and is needed for the normal structure and function of

mucous membranes and the skin.

Food sources

Milk, eggs, rice, fortified breakfast cereals, liver,

legumes, mushrooms and green vegetables are

all sources of riboflavin.

Niacin (nicotinic acid)Niacin is required for the release of energy from food. Niacin is also required for the normal

function of the skin and mucous membranes and for normal functioning of the nervous system.

Deficiency

Deficiency of niacin results in the disease pellagra. It is characterized by sun-sensitive skin

producing effects similar to severe sunburn.

Food sourcesMeat, wheat and maize flour, eggs, dairy products and yeast are all dietary sources of niacin.

Vitamin B6

(Pyridoxine)

Vitamin B6

comprises 3 forms: pyridoxine, pyridoxal and pyridoxamine, and has a central role in

the metabolism of amino acids. It is involved in breaking down glycogen and has a role in the

modification of steroid hormone action. It is also essential for the formation of red blood cells and

the metabolism and transport of iron.


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Deficiency

Deficiency of vitamin B6

is rare because it is widely distributed in foods and is synthesised by the

bodys gut flora.

Food sourcesPoultry, white fish, milk, eggs, whole grains,

soya beans, peanuts and some vegetables are

sources of vitamin B6.

Vitamin B12

(Cyanocobalamin)

Vitamin B12

serves as normal function of the nervous system, the formation of red blood cells and

for the metabolism of fol ate. Together with fol ate and vitamin B6, vitamin B

12is required for

maintenance of normal blood hormocysteine levels. It is also involved in energy production.

Deficiency

Dietary deficiency is rare in younger people and only occurs among strict vegans.

Food sources

Vitamin B12

is found in almost all foods of

animal origin. Green plants provide none but itcan be synthesized by some algae and bacteria,

although the bioavailability of such forms has

been disputed. Meat, fish, milk, cheese, eggs,

yeast extract and fortified breakfast cereals are

all dietary sources.


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Vitamin C (ascorbic acid)

Vitamin C has antioxidant properties, potentially protecting cells from oxidative damage. Vitamin C

is also involved in the synthesis of collagen which is required for the normal structure and function

of connective tissues such as skin, cartilage and bones. It is therefore an important nutrient for the

healing process.

Deficiency

Severe deficiency of vitamin C leads to scurvy. Signs of deficiency do not manifest until previously

adequately nourished individuals have been deprived of vitamin C for 4-6 months. Deficiency is

associated with fatigue, weakness, aching joints and muscles. Most of the other symptoms of scurvy

are due to impaired collagen synthesis and are characterized by bleeding gums, poor wound healing

and damage to bone and other tissues.

Food sources

Fresh fruits especially citrus fruits and berries;

green vegetables, peppers and tomatoes are all

sources of vitamin C. It is also found in potatoes

(especially new potatoes).

Vitamin supplementsAlthough most people are able to meet their requirements for vitamins by eating a varied diet, there

are certain groups of the population who have higher than normal requirements for some nutrients,

e.g. ill people, those taking certain drugs and pregnant women. Such people need to ensure they eat

foods rich in particular vitamins and sometimes supplements are advised. Infants and youngchildren are recommended to have supplements of vitamins A, C and D up to age 5 years. Vitamin

D supplements are also recommended for older people and pregnant and lactating women. Some

women may require additional iron if menstrual losses are high and folic acid is advised for women

planning a pregnancy and for pregnant women in the first 12 weeks of pregnancy.

Author

Gareth Williams

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