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 SingHealth​ group.​

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) o​f 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 cataract prevention

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.

Vitamin A for age-related macular degeneration (AMD)

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:

  1. Night blindness
  2. Dry eye (xerophthalmia)
  3. White lumps at hair follicles
  4. Loss of appetite
  5. Impaired taste and smell
  6. Poor bone growth
  7. 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:

  1. Headache
  2. Nausea and vomiting
  3. Fatigue
  4. Loss of appetite
  5. Irritability
  6. Muscle pain and weakness
  7. Blurry vision
  8. 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.

Ref: N18