Vitamin A is a naturally-occurring antioxidant that plays numerous roles in health. Vitamin A is essential to your vision, immune response, reproduction and bone health, and may play a role in preventing cancer. Vitamin A is readily available in both plant and animal food sources and is often contained in multi-vitamins.
Types
According to the National Institutes of Health, plant and animal sources provide different types of vitamin A. Plant foods offer provitamin A carotenoid, most often in the form of beta carotene. This type of vitamin A is converted to retinol in the body, and acts as an antioxidant. Animal-based foods such as liver and whole milk provide preformed vitamin A. This type of vitamin A is already in the form of retinol and is the type most easily used by the body.
Recommended Dietary Allowance Animal Sources
The RDA for retinol, or animal-based vitamin A, is expressed in international units, or IUs. In general, males over age 14 should consume 3,000 IUs per day, and females should consume 2,300. Pregnant and lactating women need a bit more, while children require less. The Tolerable Upper Limit, or maximum safe dosage, is 10,000 IUs per day for everyone over age 19, and 9,240 for teens.
Recommended Dietary Allowance Plant Sources
The Recommended Dietary Allowance guidelines do not cover carotenoids, or plant-based vitamin A sources. Instead, adults are advised to consume five or more servings of fruits and vegetables per day, including dark green vegetables and yellow or orange fruits.
Vitamin A Deficiency
Rarely seen in developed countries but common in the developing world, vitamin A deficiency can cause vision problems including blindness, immune system disorders and respiratory infections. The risk of deficiency is greater in children living below the poverty line or suffering from chronic illness, and people of any age with Celiac disease or other malabsorption disorders. Vegetarians may be at risk of deficiency if they do not consume at least five servings of fruits and vegetables per day.
Vitamin A Toxicity
Too much vitamin A can cause serious health problems and even death. Acute symptoms often include dizziness, headache, loss of coordination and gastrointestinal distress. Overconsumption of vitamin A can also cause birth defects, liver problems, osteoporosis and disorders of the central nervous system. These effects are generally associated with animal-based sources and supplements rather than plant-based beta carotene.
Supplements
According to the National Institutes of Health, vitamin A supplements are generally not needed or recommended, as vitamin A is readily available in food and is stored in the body. However, many multi-vitamins include vitamin A. Unless your doctor advises otherwise, choose a supplement with as little vitamin A as possible, and try to choose one that provides beta carotene rather than retinol. This is particularly important for pregnant women taking prenatal vitamins, as high levels of vitamin A could cause birth defects. Always check with your physician before adding any new supplements.
Retinoids
Synthetic compounds similar to retinol, retinoids are sometimes prescribed for skin conditions. While these medications can be safe and effective, they can be toxic in high doses. Follow your doctor's instructions carefully and avoid becoming pregnant during treatment.
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