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 µg (3.33 i.u.) retinol = 6 µg Beta Carotene = 12 µg 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 Skin : Vitamin A maintains healthy skin and mucous membranes - helping to prevent against Infection of the nose, throat, lungs, urinary tract etc. Eyes: The vitamin is necessary in the formation of visual purple, an eye pigment involved in night vision. Other Properties: Vitamin A is needed for proper development of the foetus in the womb. It also influences proper bone development. Back to Top   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. Back to Top   REQUIREMENTS Upper safe level for daily supplementation = 2300µg (800µg in Pregnancy) Recommended Daily Allowance = 800µg Back to Top   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). Back to Top   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 µg (25000 i.u.) in women and 9000 µg (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 µg 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. Back to Top   INTERACTIONS AND CONTRA-INDICATIONS Zinc: A deficiency of the mineral Zinc can affect the function of vitamin A and vice versa. Acne Drugs: Vitamin A should not be taken with vitamin A-derivative acne drugs. Back to Top   FOOD SOURCES Food (µg/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 REFERENCES: 1. Futoryan T, Gilchrest BA. Retinoids and the skin. Nutr Rev, 52;9:299-310, 1994. 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. Back to Top   Related News Stories Studies support the use of a multivitamin supplement in reducing the risk of colon cancer.   A lower risk of Colon Cancer Multivitamins and vitamin E intakes may help decrease the risk of colon cancer, studies suggest.   Treatment of childhood eczema Health factors which may help relieve the symptoms of eczema   Antioxidants protect against osteoarthritis A study into the effect of antioxidants on the progression and development of osteoarthritis   Nutrient deficiencies linked to infection   Look out for the benefits of antioxidants! Scientists debate whether antioxidant nutrients should be advocated as a preventative against age-related macula degeneration (ARMD).   Multivitamins for pregnancy Studies in the developing world show the benefits of supplementing with a multivitamin, whilst pregant, for the health of the baby, particularly in guarding against infection. Back to top