Vitamin A is a fat-soluble vitamin. There are different forms of vitamin A including retinol, retinal, retinoic acid, and retinyl ester, which are collectively referred to as ‘retinoids’. The strongest form of vitamin A is retinol.
Why you may need vitamin A
Acne, eczema, psoriasis – vitamin A is important for maintenance of epithelial tissue, which covers the external surface of your body – your skin.
Cataracts – a high dietary intake of vitamin A is associated with a reduced risk of cataracts.
Urinary, respiratory, gastrointestinal and vaginal infections – vitamin A assists immune function and increases resistance to infection. The linings inside our body are made up of epithelial tissue called mucous membranes. These include linings of the mouth, nose, stomach, intestines, lungs, bladder and vagina. Vitamin A is important for helping to maintain healthy mucous membranes. Changes in this lining can increase the susceptibility to infection.
Anaemia – vitamin A deficiency can impair iron mobilisation from body stores.
How much do you need?
Recommended Daily Intake (RDI)
Adults (over 19 years): 700mcg (women), 900mcg (men) retinol equivalents daily
Pregnancy: 800mcg retinol equivalents daily
Breastfeeding: 1,100mcg retinol equivalents daily
Children 9-13 years: 600mcg retinol equivalents daily
Children under 14-18 years: 700 (girls), 900mcg (boys) retinol equivalents daily
Note: 1IU = 0.3mcg retinol equivalents
Symptoms of deficiency
Symptoms of deficiency include the following – night blindness, xerophthalmia (the cornea and conjuctiva become dry, thick and wrinkled), bitots spots (triangular grey spots on the eye), visual impairment and blindness, dryness of the skin, plugged hair follicles, increased susceptibility to respiratory, urinary tract and vaginal infections, diarrhea, loss of appetite, anemia, stunted bone growth in children and tooth decay.
The best dietary sources of vitamin A include eggs, whole milk, butter, meat, animal liver and fish liver oils eg cod and halibut (the liver stores retinol – vitamin A).
Other reasons why you may need more
Good digestion plays a very important role in maintaining adequate vitamin A levels. You may need more if you have a malabsorption disorder such as coeliac disease, cystic fibrosis, pancreatic disease or cirrhosis of the liver. If fat absorption is difficult for you, best to choose a water-miscible vitamin A supplement.
Gastrointestinal infections or infestations such as giardia and hookworm can reduce vitamin A absorption.
The liver is the main organ that stores retinol. Conditions such as marasmus and kwashiorkor are caused by severe protein malnutrition. The liver reduces the release of retinol and doesn’t increase until protein status has normalised.
If you are zinc deficient, your vitamin A levels may not be too crash hot either. Zinc is required in the liver for synthesis of retinol binding protein and without adequate zinc, vitamin A also suffers.
- If you have liver disease or drink alcohol in excess, there is an increased risk of vitamin A toxicity. Your liver can only handle so much!
- High doses of vitamin A have been shown to be cause birth defects. Studies have been done to work out the threshold. The levels in studies vary from 10,000–30,000 IU daily.
- If you are pregnant, do not take vitamin A supplements without consulting your doctor first.
- During pregnancy a well-balanced healthy diet should cover your vitamin A requirements and further supplementation should not be necessary. You should discuss any conditions you have with your healthcare professional to assess if they may influence your vitamin A status.
- Large doses of vitamin A increase the need for vitamin E to protect against the oxidation effects of vitamin A.
- Excessive intake of vitamin A (hypervitaminosis) can lead to a deficiency in blood clotting factor thrombin, causing increased bleeding time. Vitamin K can correct the problem.
- Since vitamin A is a fat-soluble vitamin it can be stored and easily accumulated in the body. Always check with your healthcare professional when supplementing with high doses of vitamin A. Toxicity symptoms include severe headache, sore mouth, bleeding gums, dizziness, loss of appetite, nausea, vomiting, diarrhoea, weight loss, blurred vision, irritability, fatigue, insomnia, painful bones, dry itchy peeling skin, rashes, cracked lips, hair loss, brittle nails, cessation of menstruation, high calcium and lipids in the blood and jaundice.