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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

A (Vitamin A)

DESCRIPTION

Vitamin A (retinol) only occurs in its preformed state in animal foods. One microgram of retinol is known as one Retinol Equivalent and the latter is also a term by which plant precursors of vitamin A are measured:
1 R.E. = 1 g (3.33 i.u.) retinol = 6 g Beta Carotene = 12 g other provitamin A Carotenoids


STABILITY

Vitamin A is one of the fat-soluble vitamins. The vitamin is sensitive to oxygen, acids and ultraviolet light but is slightly more stable in its "ester" form (i.e. as vitamin A palmitate or acetate).


FUNCTIONS

Eyes:
The primary role of vitamin A is in vision. The vitamin is essential for the formation of visual purple, an eye pigment involved in night vision.

Cell differentiation
Vitamin A also has an important role in cell differentiation and so is necessary for the formation of new cells.

Skin and mucus membranes
Vitamin A has a role in maintaining the health and integrity of the Skin and mucus membranes, helping to prevent against Infection of the nose, throat, lungs, urinary tract etc.

Other Properties:
Vitamin A also functions in foetal and bone development, appetite, taste, hearing, growth and the production of sperm.


DEFICIENCY

Severe vitamin A deficiency leads to various physical changes in the eye and eventually leads to blindness. A marginal vitamin A deficiency will lead to increased susceptibility to respiratory tract Infections and skin problems.


REQUIREMENTS

Upper safe level for daily supplementation = 2300g (800g in Pregnancy)

Recommended Daily Allowance = 800g


SUPPLEMENTAL USES

Vitamin A can be taken by anyone who is worried that they may be at risk of marginal vitamin A deficiency. This could include:

  • Vegetarians
  • Slimmers
  • Those with fat malabsorption syndrome

Vitamin A has also been used successfully in the treatment of certain Skin conditions, e.g. Acne and Psoriasis (1,2).

In the developing world where vitamin A deficiency is very severe, mega dosages of around 300,000 i.u. are given to children on a yearly or six monthly basis. Sadly, despite this, there are about 6-7 million new cases of blindness each year as a result of vitamin A deficiency (3).


SAFETY

Vitamin A is one of the vitamins that if taken in excess can lead to toxicity because it is stored in the liver. However it still has a higher safety margin in that regular daily intakes generally have to exceed 7500 g (25000 i.u.) in women and 9000 g (30000 i.u.) in men before toxic side effects are experienced.

Because very high intakes of vitamin A have been reported to cause birth defects (4) (no such cases have been reported in the UK), the Chief Medical Officer advises that pregnant women should not eat liver. Also, supplements of more than 800 g vitamin A have to carry a warning for pregnant women not to take them.

The effects of vitamin A excess would take the form of Skin scaling, joint pains, liver enlargement and nausea (5). Vitamin A toxicity is usually fully reversible.


INTERACTIONS AND CONTRA-INDICATIONS

Zinc:
A deficiency of the mineral Zinc can affect the function of vitamin A and vice versa.

Certain drugs can intereact with vitamin A and so anyone using prescribed medication should consult a medical practitioner before supplementing with the vitamin.

Adverse reactions have been reported between vitamin A and cholesterol lowering drugs.

Some patients have experienced Headaches and double vision after combining vitamin A with the tetracycline antibiotic Minocycline.

Side effects have been reported after using vitamin A in combination with certain drugs prescribed for the treatment of Acne.


FOOD SOURCES

Food (g/100g) (i.u./100g)
Halibut liver oil 3000000 900000
Lamb's liver 66333 19900
Cod liver oil 60000 18000
Carrots (old) 6667 12000
Butter 3283 985
Margarine 2667 800
Cheese, cheddar 1210 363
Eggs 633 190
Pig's kidney 533 160
Milk 187 56
Mackerel 150 45
Beef 33 10
Sardines, canned 23 7


FURTHER RESEARCH

Vitamin A is an essential micronutrient with important roles in ummunity and maintenance of noemal epithelial cell differentiation. Little information is availableregarding the relationship between Vitamin A concentrations and asthma despite the repair of epithelial and other structural changes being of utmost importance for the relief of symptoms and control of the disease. The authors evaluated Vitamin A concentrations in well-nourished children with asthma.

Results found that the mean serum Vitamin A concentrations were significantly lower in asthmatic children than controls.

The data suggests that there is a correlation between Vitamin A deficiency and the mechanism of asthmatic response.

Pediatr Int. 2006 Jun; 48 (3):261-4

Nutrition and bronchopulmonary dysplasia

Nutrition plays a critical role in the prevention and management of bronchopulmonary dysplasia (BPD). Growth failure in infants with BPD is predominantly due to malnutrition. Malnutrition can worsen BPD by compromising lung growth. Feeding difficulties in these infants can further affect nutrition. Nutritional management of very low birth weight (VLBW) infants should be addressed from the first day of life to enhance growth and minimize respiratory morbidity. Fluid restriction, parenteral nutrition with protein and lipids, and early enteral feeding may help decrease the incidence of BPD. High calorie concentrated formula can be used in infants to achieve adequate growth if total daily fluid intake is restricted. Vitamin A supplementation may help to prevent further damage to lungs.
Semin Perinatol. 2006 Aug;30(4):200-8.

HERBS

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NUTRITIONAL SUPPLEMENTS

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REFERENCES

1. Proc Nutr Soc. 2002 Aug;61(3):397-400.
2. Fleischer AB Jr et al. Alternative therapy is commonly used within a population of patients with Psoriasis. Cutis, 58;3:216-220, 1996.
3. Human Nutrition and Dietetics, J S Garrow & W P T James, Churchill Livingstove, 1993.
4. Rothman KJ et al. Teratogenicity of high vitamin A intake. N Engl J Med, 333;21:1369-1373, 1995.
5. Dietary Reference Values for Food, Energy and Nutrients for the United Kingdom Dept of Health, HMSO,1991.

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