All you need to know about vitamin A
Vitamin A is an important fat-soluble vitamin that supports your immune system, vision, reproductive health, and fetal growth. Even though it’s essential to get enough, taking too much can be harmful.
Vitamin A plays a vital role in your body. It exists naturally in foods and can also be consumed through supplements.
This article discusses vitamin A, including its benefits, food sources of the vitamin, and the effects of deficiency and toxicity.
What is vitamin A?
Though vitamin A is often considered a singular nutrient, it’s really a group of fat-soluble compounds, including retinol, retinal, and retinyl esters.
Two forms of vitamin A are found in food.
Preformed vitamin A — retinol and retinyl esters — 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.
To use both of these forms of vitamin A, your body must convert them to retinal and retinoic acid, the active forms of the vitamin.
Because vitamin A is fat-soluble, it’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.
These esters are then broken down into all-trans-retinol, which binds to retinol-binding protein. It then enters your bloodstream, at which point your body can use it.
Functions in your body
Vitamin A is essential for your health. It supports 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.
It also helps protect and maintain the cornea, which is the outermost layer of your eye, and the conjunctiva, a thin membrane that covers the surface of your eye and the inside of your eyelids.
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 cells that protect your body from infection.
What’s more, vitamin A supports skin cell health, male and female reproductive health, and fetal development.
Health benefits
Vitamin A is an important nutrient that benefits health in many ways.
Potent antioxidant
Provitamin A carotenoids such as beta carotene, alpha carotene, and beta cryptoxanthin are precursors of vitamin A and have antioxidant properties.
Carotenoids protect your body from free radicals — highly reactive molecules that can harm your body by creating oxidative stress.
Oxidative stress has been linked to chronic conditions such as diabetes, cancer, heart disease, and cognitive decline.
Diets high in carotenoids are associated with a lower risk of many of these conditions, such as heart disease, lung cancer, and diabetes.
Essential for eye health and preventing 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%.
This risk reduction is linked to carotenoid nutrients’ 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 more than 10,000 adults found 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 nonsmokers with the lowest intake of these nutrients.
What’s more, test-tube studies demonstrate that retinoids may inhibit the growth of certain cancer cells, such as bladder, breast, and ovarian cancer cells.
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 cells 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.
Food sources
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 body’s ability to effectively convert carotenoids, such as beta carotene, into active vitamin A depends on many factors — including genetics, diet, overall health, and medications.
For this reason, those who follow plant-based diets — especially vegans — should be vigilant about getting enough carotenoid-rich foods.
Foods highest in preformed vitamin A include:
- egg yolks
- beef liver
- liverwurst
- butter
- cod liver oil
- chicken liver
- salmon
- cheddar cheese
- liver sausage
- king mackerel
- trout
Foods high in provitamin A:
- sweet potatoes
- pumpkin
- carrots
- kale
- spinach
- dandelion greens
- collard greens
- winter squash
- cantaloupe
- papaya
- red peppers
Toxicity and dosage recommendations
Just as vitamin A deficiency can negatively impact health, getting too much can also be dangerous.
The Recommended Dietary Allowance (RDA) for vitamin A is 900 mcg and 700 mcg per day for men and women, respectively. This intake level is easy to reach if you consume plenty of whole foods.
However, to prevent toxicity, it’s important not to exceed the Tolerable Upper Intake Level (UL) of 10,000 IU (3,000 mcg) per day for adults.
Though it’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.
Since vitamin A is fat-soluble, it’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 you ingest extremely high doses.
Acute vitamin A toxicity occurs over a short time period when a single excessively high dose of vitamin A is consumed. Chronic toxicity occurs when doses more than 10 times the RDA are ingested over a longer time span.
The most common side effects of chronic vitamin A toxicity — often referred to as hypervitaminosis A — are:
- vision disturbances
- joint and bone pain
- poor appetite
- nausea and vomiting
- sunlight sensitivity
- hair loss
- headache
- dry skin
- liver damage
- jaundice
- delayed growth
- decreased appetite
- confusion
- 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.
What’s more, vitamin A toxicity can negatively impact the health of pregnant people and their babies and may lead to fetal development irregularities.
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 and to vitamin A supplements.
A 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 people who smoke cigarettes.
Since too much vitamin A can be harmful, consult a healthcare professional before taking vitamin A supplements.
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. Therefore, while it’s crucial to meet the RDA of 700–900 mcg daily for adults, it’s also essential not to exceed the daily upper limit of 3,000 mcg.
A healthy, balanced diet is a great way to provide your body with a safe amount of this essential nutrient.
