Vitamin A plays an important role in maintaining good vision and healthy skin and bones. Pharmacists from the Retail Pharmacy at Changi General Hospital give an overview of vitamin A.
Vitamin A deficiency is rare in developed countries such as Singapore as vitamin A is easily obtained from food. Rather, the main concern with this fat-soluble vitamin is toxic overload. "If you are consuming more than 2,500 IU (750 mcg) of vitamin A daily, you are probably having too much of a good thing," say pharmacists from
Retail Pharmacy at
Changi General Hospital, a member of the
All about vitamin A
According to pharmacists, since vitamin A is a fat-soluble vitamin, any excess might not be passed out but will be stored in the body tissues, predominantly the liver. Any excessive buildup can lead to a toxic syndrome known as hypervitaminosis A.
Nutritional supplement use is intended to prevent nutritional deficiencies, or maintain the present nutritional status, not for the self-treatment of vitamin deficiencies. Those who have conditions that predispose them to vitamin A deficiency such as cystic fibrosis, pancreatitis and biliary obstruction, or are suffering from chronic alcoholism, should seek medical advice from the doctor.
The Recommended Dietary Allowance (RDA) of vitamin A for a normal healthy adult in Singapore is 2,500 IU (750mcg retinol) daily. Most commercially available health supplements contain vitamin A in the range of 2,500 to 10,000 IU.
Best food sources of vitamin A
There are two main forms of vitamin A: Pre-formed vitamin A (retinol, retinal, retinoic acid, and retinyl esters) and pro-vitamin A carotenoids (beta-carotene and others).
You can get vitamin A directly from animal sources (retinol), or indirectly from plant sources (carotenoids and beta carotene, which the body converts to vitamin A).
Animal sources of vitamin A:
Eggs, beef and chicken liver, dairy products (such as milk, butter and cheese)
Plant sources of vitamin A:
Dark, leafy vegetables (kale, spinach, kai lan), orange-coloured fruits and vegetables (apricots, papaya, mango, cantaloupe, winter squash, sweet potatoes, capsicum)
Why you need vitamin A
You need vitamin A for good vision (especially night vision), healthy skin and bones, healthy reproductive organs and foetal development. The elderly and malnourished, the chronically ill and those with gastro-intestinal problems, such as inflammatory bowel disease and Crohn’s disease, are more susceptible to vitamin A deficiency.
Vitamin A for
Current data does not support the use of antioxidants (beta-carotene, vitamin C, vitamin E) in the prevention of cataract. The effects of beta-carotene alone, or in combination with other antioxidants, have not been shown to prevent or slow cataract progression.
In the Age-Related Eye Disease Study (AREDS), taking a supplement containing a high dose of antioxidants (beta-carotene, vitamins C and E) combined with zinc, was found to slow the progression of the disease in patients with certain forms of intermediate or advanced AMD.
The effect of beta-carotene alone on AMD was not measured in this study. Smokers should not use this supplement unless directed by their physicians. Beta-carotene supplementation has been shown to increase the risk of lung cancer in smokers.
Vitamin A for
dry eyes (xerophthalmia)
Vitamin A is indicated in the prevention and treatment of the symptoms of vitamin A deficiency, such as dry eye (xerophthalmia) and night blindness. Therapeutic doses of vitamin A for the treatment of this condition should never be undertaken without close medical supervision.
Vitamin A to improve skin condition
Prescriptive skincare products containing vitamin A analogs are used to treat acne, lighten dark spots and reduce fine wrinkles. Oral vitamin A analogs have also been prescribed to treat acne, psoriasis and other skin conditions, although not without side effects.
Massive overdoses of vitamin A however, can also cause dry skin and lips, cracking, scaling, itchy and extensive skin peeling.
Signs of vitamin A deficiency
The most common signs of vitamin A deficiency include:
- Night blindness
- Dry eye (xerophthalmia)
- White lumps at hair follicles
- Loss of appetite
- Impaired taste and smell
- Poor bone growth
- Frequent eye and viral infections
However, these can have other causes too, and you should not try to self-medicate by taking high doses of vitamin A.
Signs of vitamin A toxicity
High doses of vitamin A supplements can lead to vitamin A toxicity. Look out for these signs:
- Nausea and vomiting
- Loss of appetite
- Muscle pain and weakness
- Blurry vision
- Peeling of the skin, brittle nails
One should always try to obtain all the nutrients required from a balanced diet. Supplementation may be considered for individuals who have a poor diet low in vitamin A and no other underlying medical conditions.
If your dietary intake of vitamin A is already adequate, supplementation is not necessary, except as advised by your doctor.