BY AMY CAMPBELL, MS, RD, LDN, CDCES | JANUARY 11, 2023
This is the first piece in a series on vitamins and minerals, also called micronutrients. In this series, we’ll cover what each micronutrient does, food sources, supplements, and signs of deficiencies and excess.
Think of vitamin A and you might think about your eyes or maybe how carrots are a good source. Beyond that, you might not think too much about it at all! This week, we’ll delve a bit deeper into the inner workings of vitamin A, how much you need, and where it’s found.
What is vitamin A?
Vitamin A is called a fat-soluble vitamin because it’s absorbed with fat in the diet and is stored in the body’s fat tissue and in the liver. (Other fat-soluble vitamins are vitamins D, E, and K.)Advertisement
There are two different sources of vitamin A:
- Preformed vitamin A (retinol, retinyl esters): This is found in animal foods, fortified foods, and supplements.
- Provitamin A carotenoids: These are turned into vitamin A in the body and are found in plant-based foods, including fruits and vegetables. Beta carotene is the most common type of provitamin A, but other types include lycopene, lutein, and zeaxanthin.
What does vitamin A do?
Vitamin A is needed for the formation and health of:
- Teeth
- Skeletal and soft tissue
- Mucous membranes
- Skin
- The immune system
- Reproduction
It also supports good eyesight (that’s where the carrots come in!), especially in low light. And it plays a role in supporting healthy pregnancy and breastfeeding.
The carotenoids, of which there are at least 600, act as antioxidants in the body. This means that they protect against oxidative damage caused by free radicals. Some carotenoids, such as zeaxanthin and lutein, protect against age-related macular degeneration. Lycopene, for example, may play a role in bone health, a reduced risk of stroke, and possibly, a lower of prostate cancer.
What foods have vitamin A?
Vitamin A is naturally found in many foods, and it’s also added to some foods, such as milk and cereal. Many fruits and vegetables, as well as supplements, contain carotenoids. Some of the main food sources of vitamin A include:
- Leafy green vegetables (kale, spinach, broccoli)
- Orange, red, and yellow vegetables (e.g., carrots, sweet potatoes, winter squash, red peppers, tomatoes)
- Cantaloupe and mango
- Milk and cheese
- Eggs
- Beef liver and other organ meats
- Salmon and herring
- Fortified breakfast cereals
Vitamin A may be in certain supplements in the form of retinyl acetate, retinyl palmitate, beta carotene, or a combination of all three. Most multivitamins contain vitamin A, and you can find supplements that only contain vitamin A or beta carotene.
How much vitamin A do you need?
The amount of vitamin A that you need depends on your age and sex. The Institute of Medicine’s Recommended Dietary Allowances (RDA) of vitamin A are in micrograms (mcg) of retinol activity equivalents (RAE) to account for different absorption rates of preformed vitamin A and provitamin A carotenoids.
- The RDA for vitamin A for adult males is 900 mcg RAE and adult females is 700 mcg RAE
There is also a daily upper limit for preformed vitamin A from all sources (foods, beverages, and supplements) because too much of this form of vitamin A can be harmful.
- The daily upper limit for vitamin A for adults is 3,000 mcg
What are signs of vitamin A deficiency?
Vitamin A deficiency in the U.S. is rare because most people get enough of this vitamin from the foods that they eat. A deficiency is more common in developing countries, especially in children. However, vitamin A deficiency in the U.S. may occur in:
- Premature infants
- People with cystic fibrosis
- People with Crohn’s disease, ulcerative colitis, or celiac disease
- People with cirrhosis
- People with alcoholism
- People living in poverty
Signs of vitamin A deficiency include:
- Xerophthalmia, an ability to see in low light, that can lead to blindness
- Infectious diseases such as pneumonia and measles
- Dry, scaly, and/or itchy skin
- Infertility
- Delayed growth and development in children
Signs of vitamin A toxicity include:
Too much of preformed vitamin A from supplements or certain medicines can be harmful, and lead to:
- Severe headaches
- Blurry vision
- Nausea
- Dizziness
- Muscle aches
- Bone pain
- Sensitivity to bright light
- Liver failure
Too much preformed vitamin A during pregnancy can cause birth defects in the baby, so it’s important to avoid taking high-dose preformed vitamin A supplements if you are pregnant or planning a pregnancy.
On the other hand, high doses of beta carotene don’t cause the same problems as preformed vitamin A. The main side effect of high dose beta carotene is yellow-orange skin! However, this is harmless and will go away once you cut back on the amount. An exception is for smokers, former smokers, and people exposed to asbestos: High-dose beta carotene supplements are linked with lung cancer and death.
Other things to know about vitamin A
Vitamin A can interact with some medicines, including:
- Orlistat (brand names Alli, Xenical)
- Acitretin (Soriatane)
- Bexarotene (Targretin)
- Anticoagulants (blood thinners)
- Tetracycline antibiotics
Cod liver oil can contain very high amounts of vitamin A, which could be harmful, especially if you also take a vitamin A supplement. Be sure to check how much vitamin A is in the cod liver oil, if you take it. If you are taking it for omega-3 fatty acids, consider switching to another form of omega 3s that isn’t derived from fish liver, which is where fat-soluble vitamins are stored.
And, while you may never eat it, know that polar bear liver is extremely toxic due to the amount of vitamin A it contains. Avoid this at all costs!
Always tell your health care team about any dietary supplements that you take. And to be on the safe side, check with your health care provider if you are thinking of taking a vitamin A supplement.
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