Vitamin A is a fat-soluble vitamin found in many supplements and foods. Vitamin A plays a key role in vision by maintaining a clear cornea, which is the outside covering of your eye. Vitamin A helps mucous membranes and the skin to build effective barriers against bacteria and viruses. It helps the proper functioning of your immune system too. Vitamin A deficiency is not common. However, people who follow an intense weight loss diet can have significant deficiencies.
What Is Vitamin A?
Vitamin A is a group of fat-soluble compounds that play an important role in vision, bone growth and health of the immune system. It was isolated in the retina the first time, hence the name “retinol”.
Types of vitamin A
There are two types of vitamin A, depending on the type of food source it comes .Vitamin A compounds found in animal are kwon as preformed vitamin A (Retinoids) and those obtained from plant foods are called provitamin A (Carotenoids). Your body gets vitamin A directly from animal source foods where it is present as retinol.
Vitamin A from animal-derived foods is called retinol that is the most common dietary form of vitamin A. this preformed vitamin A is known as the active form of the vitamin, which your body can use just as it is. This bioactive form of vitamin A is converted into retinoic acid, retinal, and retinyl esters. Good food sources of retinol vitamin A include beef and chicken liver, whole milk and cheese.
Vitamin A obtained from colorful fruits and vegetables is in the form of “provitamin A” carotenoids (alpha-carotene, beta-carotene and beta-cryptoxanthin) are the inactive form of the vitamin found in plants. Beta-carotene is a red-orange pigment and an antioxidant found in plants and fruits, especially carrots and colorful vegetables. IT is one of the most prevalent and effective provitamin A carotenoids. These compounds are converted to the active form of vitamin A (retonil) in your body. The advantage of dietary beta-carotene is that the body only converts as much as it needs.
Vitamin A occurs in the body in the form of retinol, retinal (in the retina), retinoic acid (in the bones and mucous membranes) or retinyl palmitate (reserves stored in the liver).
8 Benefits of vitamin A
1. Preserve your vision
Vitamin A is essential for preserving your eyesight. Vitamin A also has been shown to be useful in helping with night vision. Without vitamin A, “night blindness” occurs this vitamin is needed to convert light that hits your eye into an electrical signal that can be sent to your brain. The carotenoids in vitamin A also help to protect by protecting against macular degeneration and Age-Related Decline.
Eye ointments with vitamin A are used for treating dry eyes as well as diseases in the cornea and conjunctiva. Vitamin A improves the tear film when introduced into the eye with the help of an ointment.
2. Reduce the risk of certain cancers
In general, cancer occurs when abnormal cells begin to grow or divide in an uncontrolled way. Beta-carotene acts as an antioxidant in the body and can protect against the damaging effects of free radicals and is converted to vitamin A in the body. (An atom or molecule with at least one unpaired electron, making it unstable and reactive. When free radicals react with certain chemicals in the body, they may interfere with the ability of cells to function normally. Antioxidants can stabilize free radicals).
A Brown University study in 2019 showed that People whose diets included high levels of vitamin A had a 17 percent reduction in risk for getting the second-most-common type of skin cancer, as compared to those who ate modest amounts of foods and supplements rich in vitamin A.
3. Strengthens your immune system
Vitamin A plays a pivotal role in maintaining your body’s natural defenses. It stimulates the proliferation of white blood cells and the production of antibodies. Thus, the lack of vitamin A reduces the immune response to certain viruses including that of measles, and to certain bacteria including that of tetanus. In addition, it is essential for maintaining the barrier function of the intestinal mucosa.
A 2018 study about the role of vitamin A in the system immune showed that it has both promoting and regulatory roles in both the innate immune system and adaptive immunity; therefore, vitamin A can enhance the organism’s immune function and provide an enhanced defense against multiple infectious diseases.
4. Reduces your risk of acne
Vitamin A is a powerful vitamin for your skin. Acne is a chronic, inflammatory skin disorder. Acne occur when the sebaceous glands are clogged up with dead skin and oils. These glands are found in the hair follicles on your skin and produce sebum, an oily, waxy substance that keeps your skin lubricated and waterproof.
Synthetic Vitamin A like Retina-A and natural vitamin A are the most well-known ways to effectively treat acne. In fact, vitamin A is a powerful antioxidant that helps your skin fight free radicals and acne. Free radicals can cause changes to your sebaceous glands, which results in the formation of bacteria. Vitamin A also helps reduce the production of sebum in your skin.
Vitamin A thus prevents your pores from clogging by preventing dead skin cells. It also reduces the amount of oil produced by your skin and decreases the formation of androgens. It also helps prevent inflammation and cell damage by protecting fats from oxidation.
Isotretinoin Capsule is used to treat severe cystic acne (also known as nodular acne) that has not responded to other treatment. However, this medication can have serious side effects and must only be taken under medical supervision.
5. Supports your bone health
Dietary intake is an important factor for bone health. The process of bone formation requires an adequate nutrients, such as calcium, protein, magnesium, vitamin D. However, vitamin A also is important for your bone health.
Vitamin A is important to building strong, healthy bones. Both osteoblasts (bone building cells) and osteoclasts (bone breaking down cells) are influenced by vitamin A.
A 2017 meta-analysis of observational studies found that dietary intake and blood level of vitamin A (total vitamin A, retinol or β-carotene) may differentially influence total and hip fracture risk.
6. Promotes your growth and reproduction
A 2011 study showed that vitamin A metabolite, is essential for reproduction in both the male and female, as well as for many events in the developing embryo.
Adequate levels of vitamin A during pregnancy are of critical importance for the health of pregnant women and their fetuses.
7-Increases hair growth:
Vitamin A play also a key role in hair growth. One study showed that certain retinoids increase the rate of hair growth, prolong the anagen phase of the hair cycle, play a role in converting vellus to terminal hairs, and act synergistically with minoxidil to produce more dense hair regrowth from regressing follicles than either compound alone. 
8- Contributes to cognitive health
According to a 2007 study oxidative stress contributes to brain aging. A long-term supplementation of vitamin A that acts like an antioxidant, might confer cognitive benefits.
Recommended daily Intake of vitamin A
The table below shows the recommended daily allowance (RDA) for vitamin A. RDAs for vitamin A are given as retinol activity equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids, all of which are converted by the body into retinol.
Vitamin A is listed on labels in international units (IUs). Under new FDA labeling rules, vitamin A will be listed in mcg RAE and not IU’s.
This change takes effect in 2020 and 2021. An RAE can’t be directly converted into an IU if you don’t know the source of vitamin A. Conversion rates between mcg RAE and IU are:
- 1 IU retinol = 0.3 mcg RAE
- 1 IU beta-carotene from dietary supplements = 0.15 mcg RAE1 IU beta-carotene from food = 0.05 mcg RAE
- 1 IU beta-carotene from food = 0.05 mcg RAE
- 1 IU alpha-carotene or beta-cryptoxanthin = 0.025 mcg RAE
The Tolerable Upper Intake Level (UL) for adults is set at 3,000 μg/day of preformed vitamin A. The median intake of vitamin A ranges from 744 to 811 μg RAE/ day for men and 530 to 716 μg RAE/day for women.
What is vitamin A deficiency ?
Vitamin A deficiency is rare in developed countries. however Vitamin A deficiency can be caused by low dietary intake, malabsorption or increased use or excretion due to certain illnesses. Vegans may be at risk, since pre-formed vitamin A is only found in animal-sourced foods.
One of the first signs of vitamin A deficiency is night blindness. A lack of vitamin A causes the cornea to become very dry, leading to clouding of the front of the eye, corneal ulcers and vision loss.
Here are the signs and symptoms of vitamin A deficiency.
- Dry Skin
- Dry Eyes
- Night Blindness
- Infertility and Trouble Conceiving
- Delayed Growth
- Throat and Chest Infections
- Poor Wound Healing
- Acne and Breakouts
Food sources of vitamin A
The best way to ensure you get the balance right is to consume vitamin A rich foods as part of your normal diet. Here are some of the animal foods that are sources of vitamin A and some of the plant foods that are sources of carotenoids:
Animal sources (vitamin A) :
- meat ,TurkeyLiver, Chicken Liver, Cod liver oil, Baked Eel, Goat cheese, soft, Milk (skim, 1%, 2%, chocolate, Salmon, Egg, butter
Plant sources (carotenoids):
- Baked sweet potato, Pumpkin, canned, Carrot juice, Cooked carrots, Cooked spinach, Baby carrots, Butternut squash, Dried apricots, Cantaloupe spinach, onions, peas and kale,
Vitamin A toxicity
As with any medication or supplement, excessive doses of vitamin A can be harmful. Vitamin A that comes from animal food sources is not water-soluble and therefore is not readily excreted from the body. Instead, it is stored in body fat and, if ingested in excess amounts, can build up in the body and become toxic. Overdosing on vitamin A leads to an adverse condition known as hypervitaminosis A.
Eating high amount of the active form of vitamin A from animal foods , medication or supplements can be toxic. Too much vitamin A (more than 3,000 mcg or 10,000 IU/day) will give you a headache and has been linked to bone loss. Pay particular attention to this possibility if you eat liver or take supplements.
In contrast, high intake of Beta-carotene and other provitamin A carotenoids found in fruits and vegetables don’t pose the same vitamin A toxicity risk.
A 2010 study showed that too high consumption of beta-carotene from food can lead to harmless yellow-orange discolouration of the skin, which fades when consumption is lowered.
Do you need of vitamin A supplement?
In general, if you have a balanced , healthy eating that provide enough vitamin A for your daily needs either from animal food sources of vitamin A or the carotenoid rich dark green and orange vegetables and fruit, you do not need to take a vitamin A supplement.
Some studies suggest that vitamin A supplements may benefit certain people even if their diet meets the basic requirements.
Check with your doctor for your vitamin A levels. A registered dietitian or doctor can help you decide if you should take a supplement and how much to take.
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Sabina Bastos Maia, Alex Sandro Rolland Souza, Maria de Fátima Costa Caminha, Suzana Lins da Silva, Rachel de Sá Barreto Luna Callou Cruz, Camila Carvalho dos Santos, and Malaquias Batista Filho Vitamin A and Pregnancy: A Narrative Review 2019 Mar; 11(3): 681. Published online 2019 Mar 22. doi: 10.3390/nu11030681
Grodstein F et al. A randomized trial of beta carotenesupplementation and cognitive function in men: The Physicians’ HealthStudy II.Arch Intern Med. 2007;167:2184-2190. Texte intégral : archinte.ama-assn.org