The deep yellow pigment in most fruits and vegetables can be attributed to Beta-carotene, the precursor to Vitamin A. Beta-carotene can be metabolised to vitamin A in the human body but only one sixth of dietary beta-carotene is converted to Vitamin A. The best source of Vitamin A is fish and animal products: liver, oily fish such as halibut, herring, tuna, pilchards and sardines. Here are some important functions of vitamin A:
- Vitamin A maintains healthy Skin and mucous membranes - helping to prevent against Infection of the nose, throat, lungs, urinary tract etc.
- The vitamin is necessary in the formation of visual purple, an eye pigment involved in night vision.
- Vitamin A is needed for proper development of the foetus in the womb. It also influences proper bone development.
DeficiencySevere 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.
Vitamin A has also been used successfully in the treatment of certain Skin conditions, e.g. Acne and Psoriasis (1,2).
Vitamin A & Asthma
Use of vitamin A supplements have been shown to be beneficial to respiratory tract infections. The use of Vitamin A with vitamins C & E are a good combination for asthma prevention.
Sources of Vitamin A
The main sources of vitamin A in the diet are animal products: milk, fortified margarines, cheese, egg yolk, liver, oily fish such as herring, tuna, pilchards and sardines. Vitamin A (as beta-carotene) is found in carrots, tomatoes, red peppers, green leafy vegetables, mangoes, apricots, broccoli, sweet potatoes. Table 1 shows the animal foods and vitamin A. These are better sources for vitamin A since no conversion is required by the body. Fruits and vegetables are listed in Table 2, but note the available vitamin A content is only one sixth the beta-carotene level. Diabetics are incapable of converting carotene to vitamin A.
Table 1: Animal foods and vitamin A content:
|Halibut liver oil||4000000|
|Cod liver oil||200000|
|Cheese (whole fat)||1500|
Table 2: Fruits and vegetables and beta-carotene + available Vitamin A.
|Food||(i.u. beta-carotine/100g)||(i.u. available vitamin A/100g)|
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. Tables 1 & 2 data extracted from "Give Asthma the Big A" Marian Shepherd Slee.