Vitamin A can be found in two forms in food:
Vitamin A is liposoluble and can therefore be stored in fat. The vitamin A we consume is largely stored in the liver, which releases it into the blood to be delivered to the cells and tissues as needed. Liposoluble vitamins are easier to absorb when taken with food.
What does vitamin A do?
Vitamin A plays a critical role in:
Beta-carotene, the precursor of vitamin A, helps slow the natural aging process of cells. Vitamin A also acts at the cellular level as an antioxidant, which means it protects against certain types of cancer. It is also used as the basis for medications called retinoids, which are used to treat severe acne and even some tumors.
Vitamin A doses are expressed in micrograms and in retinol activity equivalents (RAE). 1 µg RAE = 1 µg of retinol = 6 µg of beta-carotene.
Recommended Dietary Allowances for Vitamin A:
Source: Health Canada, Multi-Vitamin/Mineral Supplement Monograph, October 23, 2007.
*RAE = Retinol activity equivalents
Vitamin A exists naturally in the form of retinol exclusively in animal-based foods. It can also be found in plant-based foods in its provitamin A form (beta-carotene). A fruit’s or vegetable’s beta-carotene content is proportional to the intensity of its coloration.
Source: Health Canada, Canadian Nutrient File, versions 2001b and 2005; U.S. Department of Agriculture (USDA), National Nutrient Database for Standard Reference.
*RAE= Retinol activity equivalents.
In many developing countries, vitamin A deficiency is common, particularly in pregnant women and very young children. In the West, this problem is practically nonexistent. Vitamin A deficiency may occur in certain alcoholics or people with diseases that affect intestinal fat absorption, such as:
People with any of these problems require medical intervention and must not, under any circumstances, attempt to treat themselves by taking a vitamin A supplement. Certain types of intestinal or pancreatic surgery may have the same effects.
Smokers, people who regularly consume alcohol, and pregnant women have specific vitamin A requirements and must therefore more carefully monitor their intake.1
Signs of vitamin A deficiency:
Too much vitamin A is possible only through an excess of retinol, because the body transforms carotene into vitamin A only as needed. Doses of vitamin A 10 times higher than the recommended dietary allowance (RDA) are considered toxic.
Signs of excess vitamin A:
Natural health products or vitamin supplements:
Medications that may hinder vitamin A absorption:
Medications that could increase vitamin A absorption:
If you take a vitamin A supplement, take it either one hour before or two hours after taking any of the types of medications mentioned above.
1Speak with your pharmacist if you plan to take vitamin A supplements. Your pharmacist can help you choose the solution that’s best for you based on your health and any drugs you take.
Vitamin A, Retinol, Retinoic acid, Beta-carotene, ß-carotene