Vitamin A: How it works in the body and the precursor beta-carotene

September 28, 2026approx. 14 minutesby mybody®x Editorial & Expert Team

In this article

What exactly is vitamin A?

Vitamin A is not a single substance, but a group of compounds with vitamin A activity. Its main active form is retinol, according to the German Nutrition Society (DGE, 2020). So when you read “vitamin A” on a package, you are reading a collective name.

The DGE describes two basic properties. Vitamin A is essential, meaning it is vital, and it is fat-soluble (DGE, 2025). Fat-soluble means that it dissolves in fat, not in water.

What is preformed vitamin A, and what is provitamin A?

Preformed vitamin A is ready-to-use vitamin A, such as retinol; provitamin A is a precursor that the body first converts into vitamin A. According to the DGE (2025), preformed vitamin A is found exclusively in animal-based foods, such as liver or cheese (DGE, 2020).

Plant-based foods such as peppers and squash instead provide provitamin A carotenoids (DGE, 2020). The most important of these is beta-carotene: according to the DGE (2025), it has a high conversion rate to retinol and is consumed in the largest quantities. Vegans therefore depend on this precursor.

In addition to retinol, this article covers two other forms. Retinal is the form the eye needs for vision, and retinoic acid is associated with the regulation of genes. The next chapters introduce both.

Our vitamin A food table shows which foods provide how much retinol or beta-carotene. It covers the amounts; here, we focus on the effects in the body.

What effect does vitamin A have on the eyes?

Vitamin A plays a key role in vision in the retina: once converted into retinal, it becomes part of visual purple, which experts call rhodopsin (DGE, 2025). The retina is the light-sensitive layer inside the eye.

D’Ambrosio et al. (2011) describe the key process: 11-cis-retinal, a specific form of retinal, serves as a light-sensitive component in vision. If you’re looking for an image to picture it, think of visual purple as a camera and 11-cis-retinal as the film inside it, the part that reacts to light.

What does vitamin A have to do with dark adaptation?

Dark adaptation can be impaired when vitamin A intake is low, before night blindness becomes noticeable (Tanumihardjo et al., 2016). Dark adaptation means that the eye adjusts to the new light conditions after a change from light to dark.

Tanumihardjo et al. (2016) describe this in the context of subclinical deficiency. Subclinical means that the deficiency is already present but has not yet caused any noticeable symptoms. According to the review, night blindness, or significantly worse vision in the dusk, occurs only afterward.

If you notice that you have more trouble finding your way around in the dusk than you used to, have it checked out first at your primary care doctor’s office or by an ophthalmologist. The cause may not be vitamin A, and that is precisely what the examination will clarify. This turns the symptom into a sign you can follow up on, rather than a worry.

What role does vitamin A play in cells and the immune system?

Vitamin A is necessary for immune function and is essential for cell differentiation (DGE, 2025). Cell differentiation is the process by which cells develop into specialized cells with a specific function.

Through this mechanism, vitamin A is involved in the development and maintenance of the function of most tissues, such as skin and mucous membranes, according to the DGE (2025). Whether more of it also helps more is addressed in the chapter on intake.

What role does the form of vitamin A called retinoic acid play in genes?

Retinoic acid probably regulates more than 500 genes, write D’Ambrosio et al. (2011). Like retinol, retinoic acid is a form of preformed vitamin A (DGE, 2025). The authors themselves say “probably,” which is why it appears here too.

What does the immune system need vitamin A for?

Vitamin A is involved in the development and function of lymphocytes, which are white blood cells (DGE, 2025). “Necessary” describes what the body needs, not what an excess might do. Our immune system guide explains how the immune system works as a whole.

Vitamin A is also involved in blood formation, according to the DGE (2025). The DGE (2025) also mentions bone mineralization, meaning the incorporation of minerals into bones. The vitamin is also involved in the development of germ cells, that is, egg cells and sperm cells (DGE, 2025).

Vitamin A also plays an important role in embryonic development, including the maturation of lung tissue, according to the DGE (2025). There is separate guidance for pregnancy, which is covered in the chapter on intake.

How does the precursor beta-carotene become vitamin A?

The enzyme BCO1 breaks down beta-carotene into vitamin A in various tissues, especially in the intestine and liver (EFSA, 2024). An enzyme is a protein that triggers a chemical reaction in the body.

The body has a brake for this conversion. When vitamin A levels are adequate, it reduces the absorption of beta-carotene into intestinal cells and its breakdown, according to EFSA (2024). This is a regulatory mechanism, not a guarantee: according to EFSA (2024), beta-carotene combined with high amounts of preformed vitamin A could contribute to high stores in the liver.

According to EFSA (2024), vitamin A toxicity caused solely by provitamin A carotenoids has not been described in the scientific literature to date. This clearly distinguishes the precursor from preformed vitamin A.

How much vitamin A is produced from beta-carotene?

Less than the amount of beta-carotene might suggest: In a mixed diet, the ratio of retinol to beta-carotene is 1:9 to 1:16 (EFSA, 2024). So 9 to 16 parts beta-carotene produce one part retinol.

EFSA (2024) considered the food itself to be the most important influencing factor, more specifically the food matrix, meaning the structure in which the nutrient is embedded. For spinach and carrots, the ratio was less favorable than 1:15 (EFSA, 2024).

To make the two forms comparable, the DGE uses retinol activity equivalents, or RAE for short: 1 µg RAE equals 1 µg retinol or 12 µg beta-carotene (DGE, 2020). For beta-carotene from a mixed diet, the DGE (2025) therefore uses a conversion rate of 12:1.

Retinol and beta-carotene compared · DGE 2020 and 2025, EFSA 2024

The brake mentioned at the beginning of the chapter is described in more detail by EFSA (2024): A high vitamin A status activates the regulatory factor ISX in the intestinal wall, a protein that helps determine which genes a cell reads. ISX then reduces the uptake of beta-carotene into cells and its cleavage by BCO1 (EFSA, 2024).

Where does the body store vitamin A?

Mainly in the liver: In healthy people, about 70 to 90% of the body’s retinol is stored there (EFSA, 2024). In cases of severe deficiency, this proportion can fall to 50% or less (EFSA, 2024).

In the blood, retinol is bound to RBP4, a transport protein whose name stands for retinol-binding protein (EFSA, 2024). To put it in perspective, the liver is the warehouse and RBP4 is the delivery truck that carries retinol through the blood.

Tanumihardjo et al. (2016) add details about transport. Normally, the transport protein is about 85% loaded with retinol. When loaded, it forms a complex in the blood with transthyretin, the transport protein for thyroid hormones. It is also considered a negative acute-phase protein, meaning a protein whose levels fall during infections and inflammation; retinol levels in the blood fall along with it (Tanumihardjo et al., 2016).

What does the vitamin A blood level tell you?

Less than you might expect. The retinol content in blood serum, the liquid component of blood, is called serum retinol; according to the EFSA (2024), it is tightly regulated by the body and is not related to usual intake. Blood levels are tightly regulated and therefore are not a sensitive indicator of an individual’s vitamin A status.

Two findings from the EFSA (2024) show what this means. Inflammation and infections can lower the average level by up to 25%, regardless of intake. Conversely, case reports describe vitamin A excess despite blood levels in the normal range (EFSA, 2024).

According to the EFSA (2024), the level does not respond to supplements either. Tanumihardjo et al. (2016) add that blood levels reflect liver stores only when those stores are very low.

For you, this means that a single blood test is just a snapshot. A doctor can assess what it means in your case by considering your symptoms and medical history. If you suspect a vitamin A deficiency, discuss it with your family doctor rather than relying on a single number.

Vitamin A intake: Does more mean more?

No. For preformed vitamin A, the upper limit for adults is 3,000 µg per day (EFSA, 2024). According to the DGE (2025), it is hardly possible to consume too much vitamin A from what is naturally present in foods.

The objection seems obvious: If vitamin A is necessary for vision and immune function, more of it should have more of an effect. The answer lies in the word “necessary.” It describes a requirement, and the DGE provides reference values for that requirement. There is a separate limit for excessive intake, which the following paragraphs explain.

The upper limit is technically called the tolerable upper intake level, or UL for short. It describes the amount per day considered tolerable over the long term and is not a target. The EFSA (2024) proposes maintaining the value at 3,000 µg for both men and women; it applies exclusively to preformed vitamin A (DGE, 2025).

For comparison: The DGE (2020) recommends an intake of 850 µg RAE per day for men and 700 µg RAE for women aged 19 to under 65. The recommendation and the upper limit are two different values. One describes the requirement, the other the upper limit.

According to the DGE (2025), improper use of supplements or excessive consumption of liver can be a concern, as liver contains the highest levels of preformed vitamin A. Over time, this can cause vitamin A toxicity, or poisoning that damages the liver (DGE, 2025). Our article on the symptoms of vitamin A overdose describes the signs and when it becomes a concern.

Is there an upper limit for beta-carotene as a vitamin A precursor?

No, the EFSA (2024) could not establish an upper limit for beta-carotene. According to the EFSA (2024), there is no evidence of adverse health effects from a typical diet.

Supplements are different: according to the EFSA (2024), smokers should avoid dietary supplements containing beta-carotene. This is due to an increased risk of lung cancer observed in heavy smokers taking beta-carotene supplements (EFSA, 2024).

The EFSA (2024) advises women who are pregnant or planning to become pregnant not to eat liver products; further questions about nutrient intake should be discussed with a gynecologist. Anyone taking medication or considering a vitamin A supplement should talk to their primary care doctor first.

How can you keep track of vitamin A and other nutrients?

When it comes to vitamin A, food is the way to go: retinol comes from animal foods, while provitamin A carotenoids come from plant foods (DGE, 2020). The table linked in the first chapter shows how much is found in individual foods.

No test from mybody®x (MYBODY Lab GmbH) measures vitamin A. The VitalCheck Nutrient & Mineral Test Complete also does not measure vitamin A and cannot show or rule out a vitamin A deficiency. It provides a snapshot, not a diagnosis.

A self-collected blood sample is tested for, among other things, vitamin D3 and vitamin B12, with analysis performed by a specialist laboratory in Germany. Zinc is one of the minerals tested.

Zinc is related to vitamin A: According to Tanumihardjo et al. (2016), zinc and vitamin A work together in the body, and poor zinc status can affect vitamin A measurements. The review focuses primarily on developing countries. However, a zinc level is no substitute for checking vitamin A. If you suspect your intake is low, discuss it with your primary care doctor.

What does vitamin A’s effect mean for your everyday life?

Vitamin A’s effects take place in areas you can’t feel: in the visual pigment in the retina and in cells that develop into skin or mucosal cells (DGE, 2025). You only notice its effects when you’re getting too little or too much.

Beta-carotene isn’t a weaker copy of vitamin A, but a precursor whose conversion the body reduces when it has an adequate supply (EFSA, 2024). Preformed vitamin A from supplements or liver, on the other hand, has an upper limit. So talk to your doctor’s office before taking a supplement.

With vitamin A, more isn’t better. Having enough is.

Frequently asked questions

Read more

Sources

1. German Nutrition Society: Selected questions and answers on vitamin A (as of 2025) – dge.de
2. EFSA NDA Panel: Scientific opinion on the tolerable upper intake level for preformed vitamin A and β-carotene, EFSA Journal 22(6):e8814 (as of 2024) – europepmc.org
3. D’Ambrosio, Clugston and Blaner: Vitamin A metabolism: an update, Nutrients 3(1):63–103 (as of 2011) – europepmc.org
4. German Nutrition Society: Reference values for vitamin A (as of 2020) – dge.de

The functions of vitamin A and information on excessive intake are based on [1]. The upper limit and storage information come from [2], as do the details on blood levels and the conversion of beta-carotene. Genes and visual pigment are documented in [3], and active forms and reference values in [4]. Dark adaptation and zinc are also based on the review by Tanumihardjo et al. (2016) in the Journal of Nutrition. Product information and price as of 28.09.2026.