Vitamin A is a fat-soluble nutrient; meaning it is stored in the liver and fat cells until the body needs it. There are two forms of vitamin A. Retinol, or preformed vitamin A, is found in meat, poultry, fish, and dairy products. Fruits, vegetables, and other plant-based foods contain precursors to vitamin A. A precursor is a substance that the body uses to manufacture the vitamin A that it needs. Beta-carotene is the most common precursor for vitamin A.
Vitamin A is essential in the healthy functioning of vision, the immune system, and cell growth. It is also important in the formation and maintenance of healthy skin, teeth, mucus, heart, lungs, kidneys and other organs. Retinol is often used in the treatment of skin conditions including acne, wrinkles, and measles. It is also present in some sunscreens as a skin conditioner.
When a person does not get enough vitamin A they are more vulnerable to infectious diseases and vision problems. However, greater concern arises with over supplementation of vitamin A in the form of retinol. Retinol is stored in the body until it is used. Taking too much vitamin A in the form of retinol can lead to vitamin A poisoning. Symptoms of vitamin A poisoning include:
- Skin irritation
- Pain in joints and bones
- Liver disease
- Birth defects.
Beta-carotene supplements do not lead to vitamin A poisoning as the body uses only the amount of beta-carotene needed to make the amount of vitamin A required at the time. However, in studies where current and former smokers were given very high doses of beta-carotene over periods from 4-8 years there was a significant increase of lung cancer. The same results were not found among non-smokers.
Other recent studies have investigated the effects of vitamin A on cancer risk. In a study of over 69, 000 people with an average age of 62 researchers found that people who supplemented with beta-carotene and lycopene were 40% less likely to develop melanoma. Recently, the International Journal of Oncology found that retinol helps turn pre-cancerous breast cells back to healthy cells. Retinol had no effect on fully cancerous cells.
People at high risk for melanoma including those with prior diagnosis, family history, fair skin, history of sunburn, and a lot of moles should consult their physician before starting a vitamin A supplement.
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Vitamin A May Help Reduce Melanoma Risk
National Institutes of Health Office of Dietary Supplements http://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/