Vitamin A Requirements and Dietary Sources

Carrots are a great source of beta-carotene, a precursor of vitamin A.
Carrots are a great source of beta-carotene, a precursor of vitamin A. Pat Herman

Vitamin A is a member of the fat-soluble family of vitamins that also includes vitamin D, vitamin E, and vitamin K.

It's important for normal vision, adequate growth, and for cell division and differentiation. It's essential for immune system function because it is necessary for the production of white blood cells that help fight infections. You also need vitamin A for healthy skin and mucous membranes.

Vitamin A deficiency is rarely seen in developed countries, but when it occurs it can cause visual problems and loss of healthy immune system function.

The National Academies of Sciences, Engineering and Medicine, Health and Medicine Division has determined dietary reference intakes (DRI) for vitamin A based on age and sex. It represents the daily amount that's needed by the average healthy person, so if you have any medical issues, you should speak to your doctor about your vitamin A requirements. 

Dietary Reference Intakes

Males

1 to 3 years: 300 micrograms of retinol activity equivalents (mcg RAE) per day
4 to 8 years: 400 mcg RAE per day
9 to 13 years: 600 mcg RAE per day
14+ years: 900 mcg RAE per day

Females

1 to 3 years: 300 mcg RAE per day
4 to 8 years: 400 mcg RAEs per day
9 to 13 years: 600 mcg RAE per day
14+ years: 700 mcg RAE per day

Vitamin A is found in both plant and animal sources. Preformed vitamin A, or retinol, is found in butter, egg yolks, fish, liver, meats and whole milk.

Plant sources of vitamin A are called provitamin A carotenoids and include beta-carotene, alpha-carotene, and beta-cryptoxanthin. Your body takes these precursors and converts them to the form of vitamin A your cells need.  The carotenoids are found in dark green and yellow vegetables, as well as orange fruits and vegetables.

Vitamin A Supplements

Some studies have indicated that people with certain types of cancer have lower levels of vitamin A in the blood. And because vitamin A is involved in cell differentiation, some people have recommended taking vitamin A supplements for treating or preventing cancer, but there's no evidence for this recommendation. In the case of cigarette smokers, taking beta-carotene supplements may actually increase the risk of cancer.

You're better off getting your vitamin A from fruits and vegetables and other food sources rather than supplements. Probably due to all the other beneficial compounds.

But if you do take vitamin A supplements, be careful, especially if you're pregnant. In fact, women who are pregnant shouldn't take vitamin A supplements without speaking to a doctor first.

Taking large doses of preformed vitamin A supplements for extended periods of time may result in vitamin A toxicity. The Institute of Medicine determined tolerable upper levels to be 3,000 mcg RAE per day.

Vitamin A toxicity may lead to birth defects, liver abnormalities, and reduced bone mineral density that may result in osteoporosis.

Sources:

National Academies of Sciences, Engineering and Medicine, Health and Medicine Division. "Dietary Reference Intakes Tables and Application." Accessed April 4, 2016. http://www.nationalacademies.org/hmd/Activities/Nutrition/SummaryDRIs/DRI-Tables.aspx.

National Institutes of Health. "Vitamin A." Accessed April 4, 2016. https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/

National Institutes of Health, Office of Dietary Supplements. "Vitamin A Fact Sheet for Professionals. Accessed April 4, 2016. https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/.

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