Vitamin A is a fat soluble vitamin that serves as an aid to vision, immune system and cell growth.
Vitamin A is available in the human diet in two forms: a preformed vitamin A which includes retinol and a provitamin A carotenoid (1). Typically preformed vitamin A is found in animal products which include dairy and meat. Provitamin A is derived from beta-carotene, which is a part of the carotenoid family and is responsible for the red, orange or yellow color of fruit, oil, grains and vegetables (3). Both forms of vitamin A must be converted to retinal and retinoic acid in order to support the body’s biological functions (1-2).
Are you at Risk for Vitamin A Deficiency?
Vitamin A deficiency is more common in developing countries then in the United States. One of the first signs of Vitamin A deficiency is night blindness. There are four kinds of photopigments located in the eye that store vitamin A. One is called, Rhodopsin, which is located in the rod cells of the retina. Rhodopsin allows the rod cells to detect small amounts of light. They play an important role in the adaptation of the eye to low-light conditions and night vision. If night blindness is left untreated it could potentially lead to permanent blindness.
Vitamin A deficiency may also lead to a suppressed immune system. The beta-carotene form of vitamin A is an antioxidant. Antioxidants protect the body from damaging molecules called free radicals (5). Overtime, without antioxidants the body may be more susceptible to chronic illnesses.
How Much is Too Much?
Vitamin A dosage can range depending on if the source is either a stand-alone or multivitamin supplement. Generally the dosage of vitamin A can be between 2,500-10,000IU and can be found in both beta-carotene and retinol forms (2). Studies have been conducted to test the toxicity of vitamin A; this mostly pertains to the retinol and retinoic acid supplements due to their fat-soluble form. Plant based vitamin A, such as beta-carotene or “mixed carotenoids”, tend to be better as they carry a low risk for toxicity due to the fact that the body will only convert what it needs. If beta-carotene is taken in excess for long periods of time, it has the potential to turn the skin yellowish orange (5). This condition is not harmful and skin discoloration will go away simply by reducing the amount of beta-carotene being consumed.
Where Can We Find Vitamin A in our Daily Diets?
With a proper nutrition plan, many people are able to get their fill of beta-carotene in their daily diets. Beta-carotene is found in fruits and vegetables, and it recommended to ingest at least 5 servings per day. This will allow the body to absorb at least 3-6 mg of beta-carotene daily (5). It is also important to note that when taking a fat soluble vitamin to consume at least 3g of fat to ensure absorption (5). A couple of simple ways to do that is to either drizzle olive oil over a salad or use coconut oil to cook. When selecting coconut oil from your local super market, make sure to choose organic coconut oil that is unrefined, unbleached and made without chemicals.
Some of the top recommended beta-carotene sources are listed below (4):
- Sweet Potato
- Orange/Yellow Peppers
- Butternut Squash
- Collard Greens
What Studies are Currently Being Conducted on Vitamin A?
Since vitamin A helps support vision, it is predicted that zinc also plays a role in retinol to retinal conversion thus demonstrating that Vitamin A would only be able to support vision in the presence of adequate zinc (6). A study conducted by Robert Russell of Tufts University studied ten participants with a deficiency in vitamin A who also failed dark-adaptation test. Eight out of the ten participants were able to pass dark-adaptation test with supplementing 10,000IU of vitamin A for 4 weeks. The two participants who did not past the dark-adaptation test even after supplementing vitamin A for 4 weeks were deficient in blood levels of zinc. They were given 220mg of zinc per day for 2 additional weeks and were able to then pass the dark-adaptation test. This concluded that vitamin A can support vision with direct help from zinc (6).
- Ross CA. Vitamin A. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:778-91.
- Ross A. Vitamin A and Carotenoids. In: Shils M, Shike M, Ross A, Caballero B, Cousins R, eds. Modern Nutrition in Health and Disease. 10th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006:351-75.
- “Beta-Carotene, Lung Cancer, Heart Disease – Nutri-Facts.org.” Beta-Carotene, Lung Cancer, Heart Disease – Nutri-Facts.org. N.p., n.d. Web. 28 November 2016.
- “Top 10 Foods Highest in Beta Carotene.” HealthAliciousNess. USDA National Nutrient Database for Standard Reference, Release 26., 2015. Web. 28 November 2016.
- Enrlich, Steven. “Beta-carotene.” University of Maryland Medical Center. N.p., 27 Dec. 2012. Web. 28 Apr. 2015.
- Russell RM. The vitamin A spectrum: from deficiency to toxicity. Am J Clin Nutr. 2000;71:878-84.