💡 Key Takeaways
Table of Contents
What exactly is vitamin A?
Vitamin A is a fat-soluble vitamin, meaning it dissolves in fat and can be stored in the body, primarily in the liver. The term "vitamin A" encompasses a group of compounds with similar biological activity, which play a role in diverse processes such as vision, immune response, tissue development, reproduction, and the maintenance of organs like the heart, lungs, and kidneys.
An important characteristic is that the body cannot produce vitamin A from scratch: we must obtain it through the diet, either in the form of retinol (active form) or from carotenoids that the body will transform into vitamin A according to its needs.
Forms of vitamin A: retinol and carotenoids
When we talk about vitamin A, we are actually talking about two large families of molecules:
- Retinoids : These include retinol, retinal, and retinoic acid. They are the "active" forms of vitamin A, found primarily in foods of animal origin. The body can use them directly.
- Carotenoids (provitamin A) : These are plant pigments, such as beta-carotene, alpha-carotene, and beta-cryptoxanthin. The body converts them into retinol when needed.
This distinction is not merely theoretical: it influences bioavailability, safety, and how the diet should be structured. Retinoids are very effective, but in excess they can accumulate. Carotenoids, on the other hand, are better regulated: the body limits how much vitamin A it generates from them.
Food sources of vitamin A
Foods of animal origin (already formed retinol)
Animal-based foods provide vitamin A in its direct form, primarily as retinol or retinyl esters. Notable examples include:
- Liver (beef, chicken, pork or fish): is by far the most concentrated source.
- Egg yolk .
- Whole dairy products such as whole milk, butter, and full-fat cheeses.
- Cod liver oil and other fish liver oils.
These sources are beneficial when the diet is varied and they are present in moderate amounts. However, due to their high concentration, excessive consumption of liver or retinol supplements can easily approach tolerable upper intake levels without professional supervision.
Plant-based foods (provitamin A carotenoids)
Carotenoids, which the body can convert into vitamin A, are found in brightly colored vegetables: oranges, yellows, reds, and dark greens. Some of the best sources include:
- Carrot .
- Sweet potato or yam .
- Pumpkin .
- Red and orange peppers .
- Spinach , kale and other dark green leaves.
- Apricots, mango, cantaloupe melon .
- Microgreens rich in carotenoids, such as red cabbage, kale or spinach in tender form.
These vegetables offer a double advantage: they provide provitamin A and also supply fiber, additional antioxidants, and other micronutrients that work synergistically. In practice, a diet based on a variety of colorful plants is one of the safest ways to meet vitamin A needs without overdoing it.
How the body absorbs and uses vitamin A
As a fat-soluble vitamin, vitamin A is absorbed in the small intestine along with dietary fat. This process requires bile, digestive enzymes, and a healthy intestinal lining. Once absorbed, vitamin A travels through the lymphatic system to the liver, where it is stored as esters.
Factors that promote absorption
- Consume sources of vitamin A along with healthy fats (extra virgin olive oil, nuts, seeds, avocado).
- Maintain good gut health (avoid uncontrolled chronic inflammation, take care of the microbiota).
- To ensure adequate production of bile and digestive enzymes.
Factors that reduce bioavailability
- Chronically very low-fat diets.
- Malabsorption disorders (untreated celiac disease, active inflammatory bowel disease, intestinal resections).
- Chronic and high alcohol consumption, which alters liver metabolism.
- Zinc deficiency, which is involved in the transport of retinol.
All this means that it's not just "how much vitamin A you eat" that matters, but also the digestive and nutritional context in which it is found.
Vitamin A and vision: official claim and physiological reality
European legislation allows the following health claim for vitamin A: “Vitamin A contributes to the maintenance of normal vision.”
In practice, this legal phrase translates into several very specific processes:
- Retinal , a derivative of vitamin A, is a component of rhodopsin , a light-sensitive pigment in the retina. Without it, rhodopsin cannot function properly.
- Vitamin A makes adaptation to darkness possible, meaning that your eyes can move from a bright environment to one with low light without vision deteriorating.
- It contributes to the maintenance of the ocular surface and the mucous membranes that protect the eye.
When vitamin A intake is insufficient for a prolonged period, one of the first signs can be night blindness (difficulty seeing in low light). In severe and sustained deficiencies, more serious conditions such as xerophthalmia may appear, which can lead to irreversible vision loss.
Vitamin A and the immune system: barriers and adaptive response
Vitamin A also has an authorized claim related to the immune system: “Vitamin A contributes to the normal function of the immune system.”
Its role goes far beyond a simple, one-off "boost to the immune system." It involves:
- Maintaining the respiratory, digestive, and genitourinary mucous membranes , which act as the first line of defense against pathogens.
- The maturation of T and B lymphocytes, key cells of adaptive immunity.
- Modulating inflammation , helping the immune response to be effective without becoming excessive.
Therefore, a sustained, even moderate, deficiency can be associated with a higher risk of infections, especially in the respiratory and digestive systems. At the opposite extreme, intakes far exceeding the recommended levels have not been shown to provide any "extra" immune support; rather, they can approach risky levels if derived from retinol supplements.
Vitamin A, skin and mucous membranes: renewal and protective barrier
The third major official claim associated with vitamin A is: “Vitamin A contributes to the maintenance of normal skin and mucous membranes.”
This phrase summarizes processes that we know well at a biological level:
- Epidermal renewal : Vitamin A is involved in the rate at which skin cells mature, rise to the surface and renew themselves.
- Skin barrier integrity : skin with good structure and barrier function better protects against external agents, excessive water loss and daily micro-aggressions.
- Mucous membrane health : In the mouth, nose, respiratory tract and digestive tract, vitamin A helps to keep the epithelium intact and functional.
Through these same mechanisms, vitamin A derivatives (retinoids) are used in dermatology for various skin conditions. However, these uses are pharmacological and should always be supervised by healthcare professionals.
Growth, cell specialization, and development
European regulations also recognize that vitamin A “has a role in the process of cell specialization” and that it is “necessary for the normal growth and development of children.”
In biological terms, this means that vitamin A is involved in the expression of genes that determine what type of cell an immature cell will become. This process of “specialization” is key during embryonic development, childhood, and also in tissue repair in adulthood.
In contexts of severe deficiency, especially in food-insecure countries, vitamin A deficiency has been associated with a higher risk of complications in childhood and higher rates of morbidity and mortality in the early years of life.
Vitamin A and iron metabolism
Another authoritative claim states that “vitamin A contributes to normal iron metabolism” .
Iron is essential for forming hemoglobin and transporting oxygen in the blood, but to do its job it needs to be properly mobilized and utilized. Vitamin A helps in this process.
- It facilitates the mobilization of iron stored in the liver.
- It helps iron to be used properly in bone marrow and other tissues.
This explains why, in some cases, vitamin A deficiency can coexist with anemia or worsen its progression, even when iron intake is apparently adequate.
Recommended amounts and safety limits
Scientific bodies establish reference values to guide the safe intake of vitamin A. In Europe, EFSA has proposed reference intakes for adults of around 600–700 µg of retinol equivalents (RE) per day , slightly higher in the case of pregnancy and breastfeeding, and adjusted values for childhood and adolescence.
Furthermore, to avoid toxicity, a tolerable upper intake level (UL) is defined for preformed vitamin A (retinol from animal sources and supplements). For adults, this UL is around 3000 µg RE/day of preformed vitamin A. This is not usually achieved through a typical diet, but it is relevant when combining foods very rich in retinol (especially liver) with concentrated supplements.
Provitamin A carotenoids, on the other hand, do not have an established upper intake level (UL) in healthy individuals, as the body regulates their conversion and they are rarely associated with vitamin A toxicity. Very high and prolonged consumption can cause the skin to turn orange (carotenoderma), a reversible and benign effect.
Vitamin A deficiency: causes, signs and consequences
Most common causes
In countries with regular access to fruits, vegetables, and animal products, severe clinical vitamin A deficiency is rare. However, it can occur in specific situations such as:
- Diets very low in colored vegetables and animal foods.
- Extremely restrictive or monothematic diets (for example, based on ultra-processed foods low in micronutrients).
- Chronic intestinal absorption disorders.
- Liver diseases that alter the storage or release of vitamin A.
- Chronic high alcohol consumption.
Signs and symptoms of deficiency
Vitamin A deficiency can progress from mild to severe. The most commonly reported symptoms include:
- Night blindness or difficulty seeing in low light environments.
- Dry eyes (xerophthalmia), gritty sensation, photophobia.
- Increased susceptibility to infections , especially respiratory and gastrointestinal infections.
- Dry, rough or scaly skin , sometimes accompanied by hyperkeratosis (thickening).
- In severe and prolonged deficits, alterations in growth and in child survival .
In many cases, the deficiency does not occur in isolation, but together with other deficiencies (iron, zinc, proteins), which amplifies its impact.
Excess and toxicity: when to be careful
Just as insufficient intake is problematic, a sustained excess of preformed vitamin A (retinol) can also cause adverse effects. This is almost always observed in relation to:
- High and continuous consumption of liver (several times a week) in combination with other sources rich in retinol.
- Use of high-dose supplements without professional supervision, especially when combined with a retinol-rich diet.
Possible manifestations of chronic toxicity
- Nausea, digestive discomfort, and loss of appetite.
- Headache, irritability, fatigue.
- Bone or joint pain.
- Liver abnormalities (increased liver enzymes, liver damage).
In special situations, such as pregnancy, it is especially important to avoid excessive amounts of retinol from supplements or liver. Therefore, any supplementation with medium or high doses of vitamin A should always be evaluated by a healthcare professional.
How to integrate vitamin A into your daily routine
The good news is that, for most people, there's no need to do anything "extraordinary" to meet their vitamin A needs. The most effective approach is usually to adjust the quality of their diet and the variety of vegetables they eat.
Practical and simple ideas
- Include orange or dark green vegetables daily (carrot, pumpkin, spinach, kale, broccoli).
- Always accompany them with a source of healthy fat (extra virgin olive oil, nuts, seeds, avocado) to facilitate absorption.
- If you consume animal products, moderately incorporate egg yolk and whole dairy products , and reserve liver for special occasions (for example, once a month or according to the recommendations of your healthcare professional).
- Vary the fruits: add mango, cantaloupe melon or apricots when they are in season.
- Experiment with microgreens or tender vegetables, which concentrate carotenoids and other micronutrients in a very practical way.
If you're interested in learning more about easily incorporating plant-based micronutrients into your daily routine, you'll find a general article on microgreens and daily nutrition and another focused on key nutrients in microgreens helpful. You can link to them as related content on your blog to build your authority on the topic.
Frequently asked questions about vitamin A
Is it better to get vitamin A from animal or plant foods?
There is no single answer that works for everyone. Animal foods provide retinol, which the body uses directly, while plant-based foods provide carotenoids that are converted into vitamin A as needed. A combination of both groups, tailored to each person's lifestyle and preferences, is usually the most balanced option. In general, prioritizing brightly colored vegetables is a safe and beneficial strategy for overall health.
Can I get too much vitamin A just from eating a lot of vegetables?
In healthy individuals, it is very unlikely. The provitamin A carotenoids in vegetables are converted into retinol in a regulated manner, so they do not usually cause vitamin A toxicity. With very high and prolonged consumption, carotenoderma (an orange tint to the skin) may appear, but this is not a sign of poisoning and resolves with dietary adjustments.
Is vitamin A deficiency common in developed countries?
Severe clinical deficiency is rare in countries with stable access to fresh food. However, subclinical deficiencies or insufficient intake can occur in people with diets very low in vegetables, chronic digestive problems, high alcohol consumption, or malnutrition. In these cases, individual assessment by a healthcare professional is crucial.
Should I take vitamin A supplements as a precaution?
Most healthy adults with a varied diet do not need vitamin A supplementation. Since excess retinol can be toxic, supplementation with moderate or high doses should always be considered on a case-by-case basis, especially during pregnancy, breastfeeding, childhood, or in cases of liver or digestive disease. Optimizing diet is usually the first priority.
Does vitamin A improve existing vision problems?
Vitamin A is essential for maintaining normal vision, particularly for night vision. However, it does not correct refractive errors such as myopia, hyperopia, or astigmatism. Its role is to provide functional support and preventative benefits, not to directly treat these conditions, which still require ophthalmological evaluation.
