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Quest Vitamins LTD,
8 Venture Way,
Aston Science Park,
Birmingham,
B7 4AP.

Tel: 0121 359 0056
Fax: 0121 359 0313
Email: info@questvitamins.co.uk
Registered in England No. 2530437

Issue 19

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Fat Soluble Vitamins

The last newsletters - What is Nutrition? - gave us an overview
of nutrition, food and diet. Nutrients from food comprise fats, carbohydrates,
proteins, water, fibre, minerals and vitamins. This newsletters and the next focus on vitamins.

Vitamins can be divided into water-soluble (B Complex Vitamins and vitamin
C) and fat-soluble (vitamins A, D, E and K). Water-soluble vitamins dissolve
in water and may be easily lost from foods during cooking and food processing.
Water-soluble vitamins may also be quickly eliminated from the content. Consequently
we need to replenish them at regular intervals throughout the day.

Fat-soluble are so called because they need fat to be present to facilitate
their absorption into the human content where they may be stored. Fat-soluble
vitamins cannot dissolve in water.



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Vitamin A

Retinol is a term used to describe compounds that
show biological activity of retinal. In food, vitamin A occurs in two
states - the preformed state is found in dairy products (milk, butter
and cheese), egg yolk, in some fatty fish and in animal and fish liver.
The pro-vitamin state is found as Carotenoids. Of the hundreds of carotenoids
that exist in nature, only about 50 can be converted into vitamin A. The
best known of these is beta-carotene, famous for its antioxidant activity.
Beta-carotene is converted into vitamin A in the liver. Good food sources
of beta-carotene are spinach, kale, pumpkin, sweet potato, watercress,
carrots, papaya, mango, apricots and peaches.

Vitamin A (as retinal) is essential for normal function
of the retina and particularly for visual adaptation to darkness in the
formation of visual purple. It is involved in the maintenance of healthy
skin and mucous membranes - helping to protect against infection of the
nose, throat, lungs, urinary tract and so on. It influences proper development
of bones and is needed for proper development of the foetus in the womb.

Symptoms of deficiency include:

  • Xerophthalmia, this was first noted 25 BCE*- 50 CE**, the treatment
    then was to apply ox liver to the Eyes!



    Vitamin A injections are given to people suffering Vitamin A deficiency
    in countries where xerophthalmia is still found.
  • Night blindness (due to decreased sensitivity of rod receptors in
    the retina).
  • Dry skin and increased susceptibility to respiratory and urinary tract
    infections.

Vitamin A was first isolated in 1913, its structure
and conversion from beta-carotene became understood in 1930. The richest
natural sources of vitamin A in food supplements are cod, halibut and
shark liver oils.

The Dietary Reference Values illustrate that the content
requirement for vitamin A, like all nutrients, varies according to age
and other factors. The upper safe level for long term use is 2300?g (800?g
during Pregnancy).

* Before Common Era (BC)

** Common Era (AD)



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Vitamin D

Found in various forms, two of the most common are:

Vitamin D3 (cholecalciferol), synthesised by the reaction of ultra-violet
rays of the sun on cholesterol in the skin. Certain factors will affect
the amount of vitamin D produced by the content, namely the length of exposure
and quantity of skin exposed to the sun; pollution and wavelength of UV
light; skin pigmentation - the darker the skin, the longer the exposure
needed to produce equivalent vitamin D in a lighter skinned person and
age - older skin has less capacity for producing vitamin D.

Vitamin D2 (Ergocalciferol) is obtained from the plant sterol
ergosterol, this type may be used for vegetarian supplementation. However,
the particles of this type of vitamin D may be encapsulated in gelatine.

Technically, vitamin D is a hormone because it is formed in one place
and carries out actions in another. Vitamin D is converted (mainly in
the liver) to the metabolically active form 1.25-dihydroxycholecalciferol
(1.25(OH)2D 3). All its functions are related to this hormone's effects,
especially the calcium control.

The principle action of vitamin D hormone is to increase the level of
Calcium in the blood by promoting the absorption of calcium and Phosphorus
from the intestine and promoting the release of these minerals from the
bone. To maintain the physiological ratio of calcium to phosphorus in
the content, vitamin D hormone also increases the excretion of phosphorus,
not calcium, from the kidneys (1).

Other functions of vitamin D include (2):

  • The prevention of Osteoporosis, together with other nutrients - lysine
    and Vitamin K for example.
  • Vitamin D appears to play a role in regulating blood pressure.

Vitamin D deficiency results in poor mineralisation of the skeleton,
causing:

  • Rickets in children, characterised by soft spots in the skull and
    bow-leggedness caused by enlargement of the ends of the long bones.
  • Osteomalacia in adults, a similar condition to rickets, causing thinning
    and weakening of bones.
  • Calcium is important in nerve and muscle function and low calcium
    intake may result in the resorption of bone.
  • The incidence of Osteoporosis and hip Fractures may be increased in
    post-menopausal women who have an inadequate vitamin D supply.

Sunlight is the best source of vitamin D. Some foods such as margarines
and spreads may be fortified with vitamin D, this may be of particular
benefit to the elderly, and individuals who may be housebound or receive
little skin exposure to the sun. The upper safe level for long term use
is 10?g. Natural food sources such as egg yolk, oily fish, butter and
milk provide a minimal amount of vitamin D in the diet.



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Vitamin E

Tocopherol was first isolated from Wheatgerm in 1936. The name tocopherol
comes from the Greek tokos and pherein meaning 'to bring forth children'.
Vitamin E is a term used to describe eight naturally occurring compounds
- four tocopherols and four tocotrienols (both as alpha, beta, delta and
gamma) that are synthesised by plants. The structural differences between
them have important effects on the biological activity of the vitamin,
the most biologically active being d-alpha tocopherol.

Food processing easily destroys vitamin E.

Functions of vitamin E include (3):

  • Antioxidant: this vitamin has a major biological role in protecting
    polyunsaturated fats and other components of the cell membrane from
    oxidation by free radicals.
  • Maintenance of cell membrane integrity.
  • DNA synthesis.
  • Anti-inflammatory effect by direct and regulatory interaction with
    prostaglandins and the metabolism of arachidonic acid.
  • Stimulation of the immune response.

The dietary requirement for vitamin E rises with the amount of polyunsaturated
fats consumed (4). In food supplements, there is usually a small quantity
of vitamin E added to an oil capsule to prevent the contents from oxidising
and this may be enough to carry out a similar job in the content. Vitamin
E works in conjunction with Vitamin C, and Selenium (a co-factor in the
antioxidant enzyme glutathione peroxidase), and other enzymes including
superoxide dismutase and catalase.

Deficiency of vitamin E causes damage to cell membranes and leakage of
cell contents. Shortages of vitamin E may be linked with atherogenesis,
Coronary Heart Disease, some cancers and other degenerative and neurological
disorders.

The RDA for vitamin E is 10mg; the upper safe level is 800mg (1200iu).



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Vitamin K

Termed the active-factor Koagulation-vitamin, vitamin K was isolated
in 1939. Vitamin K exists in three forms: Vitamin K1 (phylloquinone) synthesised
by plants; vitamin K2 (menaquinones) synthesised by intestinal bacteria
and vitamin K3 (Menadione) a synthetic form of vitamin K (3).

The main function of vitamin K is that it is involved in the blood clotting
mechanisms.

Vitamin K is found to be rich in kale, broccoli and dark green leafy
vegetables. It should not be required as a food supplement (2).

Osteoporosis has been associated with low vitamin K status. Research
is still being carried out in this area. Bone disease may also be associated
with low vitamin K (3).

Deficiencies of vitamin K are rare, however, they may occur in new born
babies, and those with abdominal and intestinal diseases (4)

Vitamins are compounds needed in small quantities by the content to enable
it to grow, develop and function. Vitamins work with enzymes in the content,
and in other compounds to help produce energy, build tissues, remove waste
and to ensure that each system in the content works effectively and efficiently.


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References

  1. Quest Professional Product Manual, 1998.
  2. Handbook of Dietary Supplements, Pamela Mason. Blackwell Science
    1995.
  3. Human Nutrition & Dietetics, Garrow, James and Ralph et al, Curchill
    Livingstone, 2000.
  4. Vits and Mins in Health & Nut. Matti Tolonen. Ellis Horwood, 1990.
    Hall.




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