It exists naturally in the foods you eat and can also be consumed through supplements.
This article discusses vitamin A, including its benefits, food sources, as well as effects of deficiency and toxicity.
What Is Vitamin A?
Though vitamin A is often considered a singular nutrient, itâ€™s really the name for a group of fat-soluble compounds, including retinol, retinal and retinyl esters (1).
There are two forms of vitamin A found in food.
Preformed vitamin A â€” retinol and retinyl esters â€” occurs exclusively in animal products, such as dairy, liver and fish, while provitamin A carotenoids are abundant in plant foods like fruits, vegetables and oils (2).
To use them, your body must convert both forms of vitamin A to retinal and retinoic acid, the active forms of the vitamin.
Because vitamin A is fat soluble, itâ€™s stored in body tissue for later use.
Most of the vitamin A in your body is kept in your liver in the form of retinyl esters (3).
These esters are then broken down into all-trans-retinol, which binds to retinol binding protein (RBP). It then enters your bloodstream, at which point your body can use it (4).
Vitamin A is the generic term for a group of fat-soluble compounds found in both animal and plant foods.
Functions in Your Body
Vitamin A is essential for your health, supporting cell growth, immune function, fetal development and vision.
Perhaps one of the best-known functions of vitamin A is its role in vision and eye health.
Retinal, the active form of vitamin A, combines with the protein opsin to form rhodopsin, a molecule necessary for color vision and low-light vision (5).
It also helps protect and maintain the cornea â€” the outermost layer of your eye â€” and the conjunctiva â€” a thin membrane that covers the surface of your eye and inside of your eyelids (6).
Additionally, vitamin A helps maintain surface tissues such as your skin, intestines, lungs, bladder and inner ear.
It supports immune function by supporting the growth and distribution of T- cells, a type of white blood cell that protects your body from infection (7).
Whatâ€™s more, vitamin A supports healthy skin cells, male and female reproduction and fetal development (8).
Vitamin A is needed for eye health, vision, immune function, cell growth, reproduction and fetal development.
Vitamin A is an important nutrient that benefits health in many ways.
Provitamin A carotenoids such as beta-carotene, alpha-carotene and beta- cryptoxanthin are precursors of vitamin A and have antioxidant properties.
Carotenoids fight free radicals â€” highly reactive molecules that can harm your body by creating oxidative stress (9).
Oxidative stress has been linked to various chronic illnesses like diabetes, cancer, heart disease and cognitive decline (10).
Diets high in carotenoids are associated with a lower risk of many of these conditions, such as heart disease, lung cancer and diabetes (11, 12, 13).
Essential for Eye Health and Prevents Macular Degeneration
As mentioned above, vitamin A is essential to vision and eye health.
Adequate dietary intake of vitamin A helps protect against certain eye diseases, such as age-related macular degeneration (AMD).
Studies show that higher blood levels of beta-carotene, alpha-carotene and beta- cryptoxanthin may reduce your risk of AMD by up to 25% (14).
This risk reduction is linked to carotenoid nutrientsâ€™ protection of macular tissue by lowering levels of oxidative stress.
May Protect Against Certain Cancers
Due to their antioxidant properties, carotenoid-rich fruits and vegetables may protect against certain types of cancer.
For example, a study in over 10,000 adults determined that smokers with the highest blood levels of alpha-carotene and beta-cryptoxanthin had a 46% and 61% lower risk of dying from lung cancer, respectively, than non-smokers with the lowest intake of these nutrients (15).
Whatâ€™s more, test-tube studies demonstrate that retinoids may inhibit the growth of certain cancer cells, such as bladder, breast and ovarian cancer (16).
Vital for Fertility and Fetal Development
Vitamin A is essential for both male and female reproduction because it plays a role in sperm and egg development.
Itâ€™s also critical for placental health, fetal tissue development and maintenance, as well as fetal growth (8).
Therefore, vitamin A is integral to maternal and fetal health and to those trying to conceive.
Boosts Your Immune System
Vitamin A impacts immune health by stimulating responses that protect your body from illnesses and infections.
Vitamin A is involved in the creation of certain cells, including B- and T- cells, which play central roles in immune responses that guard against disease.
A deficiency in this nutrient leads to increased levels of pro-inflammatory molecules that diminish immune system response and function (17).
Vitamin A positively impacts health by keeping oxidative stress in check, boosting your immune system and protecting against certain diseases.
Though vitamin A deficiency is rare in developed countries like the US, itâ€™s common in developing countries, as these populations may have limited access to food sources of preformed vitamin A and provitamin A carotenoids.
Vitamin A deficiency can lead to severe health complications.
According to the WHO, vitamin A deficiency is the leading cause of preventable blindness in children worldwide.
Vitamin A deficiency also increases the severity and risk of dying from infections like measles and diarrhea (18, 19).
Additionally, vitamin A deficiency raises the risk of anemia and death in pregnant women and negatively impacts the fetus by slowing growth and development (20).
Less severe symptoms of vitamin A deficiency include skin issues like hyperkeratosis and acne (21, 22).
Certain groups such as premature infants, people with cystic fibrosis and pregnant or breastfeeding women in developing countries are more at risk of vitamin A deficiency (23).
Vitamin A deficiency can lead to blindness, increased infection risk, pregnancy complications and skin issues.
There are many dietary sources of both preformed vitamin A and provitamin A carotenoids.
Preformed vitamin A is more readily absorbed and utilized by your body than plant-based sources of provitamin A carotenoids.
Your bodyâ€™s ability to effectively convert carotenoids, such as beta-carotene, into active vitamin A depends on many factors â€” including genetics, diet, overall health and medications (24).
For this reason, those who follow plant-based diets â€” especially vegans â€” should be vigilant about getting enough carotenoid-rich foods.
Foods highest in preformed vitamin A are:
- Egg yolks
- Beef liver
- Cod liver oil
- Chicken liver
- Cheddar cheese
- Liver sausage
- King mackerel
Foods high in provitamin A carotenoids like beta-carotene include (25, 26):
- Sweet potatoes
- Carrots Kale
- Dandelion greens
- Swiss chard
- Red peppers
- Collard greens
- Butternut squash
Preformed vitamin A exists in animal foods like liver, salmon and egg yolks, while provitamin A carotenoids are found in plant foods, including sweet potatoes, kale and cabbage.
Toxicity and Dosage Recommendations
Just as vitamin A deficiency can negatively impact health, getting too much can also be dangerous.
The recommended daily allowance (RDA) for vitamin A is 900 mcg and 700 mcg per day for men and women, respectively â€” which can be easily reached by following a whole-foods diet (27).
However, itâ€™s important not to exceed the tolerable upper limit (UL) of 10,000 IU (3,000 mcg) for adults to prevent toxicity (27).
Though itâ€™s possible to consume excessive preformed vitamin A through animal- based sources like liver, toxicity is most commonly linked to excessive supplement intake and treatment with certain medications, such as Isotretinoin (28, 29).
Since vitamin A is fat-soluble, itâ€™s stored in your body and can reach unhealthy levels over time.
Taking too much vitamin A can lead to serious side effects and can even be fatal if ingested at extremely high doses.
Acute vitamin A toxicity occurs over a short time period when a single, excessively high dose of vitamin A is consumed, while chronic toxicity occurs when doses more than 10 times the RDA are ingested over a longer time span (30).
The most common side effects of chronic vitamin A toxicity â€” often referred to as hypervitaminosis A â€” include:
- Vision disturbances
- Joint and bone pain
- Poor appetite
- Nausea and vomiting
- Sunlight sensitivity
- Hair loss
- Dry skin
- Liver damage
- Delayed growth
- Decreased appetite
- Itchy skin
Though less common than chronic vitamin A toxicity, acute vitamin A toxicity is associated with more severe symptoms, including liver damage, increased cranial pressure and even death (31).
Whatâ€™s more, vitamin A toxicity can negatively impact maternal and fetal health and may lead to birth defects (32).
To avoid toxicity, steer clear of high-dose vitamin A supplements.
The UL for vitamin A applies to animal-based food sources of vitamin A, as well as vitamin A supplements.
High intake of dietary carotenoids is not associated with toxicity, though studies link beta-carotene supplements with an increased risk of lung cancer and heart disease in smokers (33).
Since too much vitamin A can be harmful, consult with your doctor before taking vitamin A supplements.
Vitamin A toxicity may cause symptoms, such as liver damage, vision disturbances, nausea and even death. High-dose vitamin A supplements should be avoided unless prescribed by your doctor.
The Bottom Line
Vitamin A is a fat-soluble nutrient vital to immune function, eye health, reproduction and fetal development.
Both deficiency and surplus intake may cause severe side effects, so while itâ€™s crucial to meet the RDA of 700â€“900 mcg daily for adults, donâ€™t exceed the upper daily limit of 3,000 mcg.
A healthy, well-balanced diet is a great way to provide your body with a safe amount of this essential nutrient.