Vitamin A Role
Vitamin A is a fat-soluble nutrient that 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.
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.
Main Functions
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.
- Vitamin A supports skin cell health, male and female reproductive health, and fetal development.
Benefits
- 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.
- Vital role of Vitamin A 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. It’s also critical for placental health, fetal tissue development and maintenance, and fetal growth. Therefore, vitamin A is integral to the health of pregnant people and their developing babies, as well as people who are trying to become pregnant.
- 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.
Deficiency
Though vitamin A deficiency is rare in developed countries such as the United States, it’s common in developing countries, where 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 World Health Organization, 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.
- Additionally, research has found that vitamin A deficiency raises the risk of anemia and death in pregnant women and negatively impacts the fetus by slowing growth and development.
- Less severe symptoms of vitamin A deficiency include skin issues such as hyperkeratosis and acne.
- Certain groups — such as premature infants, people with cystic fibrosis, and pregnant or breastfeeding people in developing countries — are more at risk of vitamin A deficiency.
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 carotenoids like beta carotene include:
- sweet potatoes
- pumpkin
- carrots
- kale
- spinach
- dandelion greens
- collard greens
- winter squash
- cantaloupe
- papaya
- red peppers
