Quest Vitamins LTD,
A (Vitamin A)
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:
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).
Skin and mucus membranes
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.
Upper safe level for daily supplementation = 2300µg (800µg in Pregnancy)
Recommended Daily Allowance = 800µg
Vitamin A can be taken by anyone who is worried that they may be at risk of marginal vitamin A deficiency. This could include:
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).
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.
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 (µg/100g) (i.u./100g)
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.
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1. Proc Nutr Soc. 2002 Aug;61(3):397-400.