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Vitamin A (retinol)

Definition: What is Vitamin A?

The vitamin retinol is also called vitamin A1 or axerophthol. Sometimes retinol is also simply equated with vitamin A, which is not entirely correct.¹ Strictly speaking, the term "vitamin A" encompasses an entire group of compounds with vitamin A activity - with retinol being the central active form.² In addition to retinol, the oxidized form retinal, as well as retinyl esters and 3-dehydroretinol, are counted among the vitamin A group of substances. Good to know: Vitamin A is one of four fat-soluble vitamins. Fat-soluble means that retinol and co. need fat as a transport medium to be optimally absorbed by the body. You should therefore consume fat, for example in the form of vegetable oil, when you eat foods containing vitamin A.³

What are the functions of vitamin A?

Retinol is classically credited with supporting visual function. Here, in the form of the vitamin A aldehyde retinal, it is part of the visual process in the retina.⁴ However, retinol can do even more: as retinoic acid, it can improve iron utilization, is involved in the differentiation of stem cells and thus in blood formation, and can support the immune system by forming white blood cells.⁵

Vitamin A for the skin?

Retinol is also important for the skin: the outermost layer of the skin, the stratum corneum, is formed in part with the help of this substance. As a result, retinol promotes skin regeneration, which makes it of interest to the cosmetics industry.⁶

Does vitamin A have an effect on mental health?

Vitamin A has no direct effect on mental health when taken in normal amounts. However, excessive intake can lead to psychological symptoms such as irritability, mood swings, or fatigue.

What makes vitamin A unique?

Together with vitamin D, it can, as retinoic acid, regulate the activity of over 500 genes by binding with its receptor to binding sites on the DNA. Vitamin A is therefore a specific transcription factor for all sorts of genes.⁷ This becomes particularly relevant in connection with the immune system and cell differentiation: vitamin A compounds, for example, stimulate the formation of antibodies and activate certain immune cells, the T-lymphocytes.⁸

If there is an iron deficiency or anemia induced by it, vitamin A together with iron can lead to a faster improvement of the condition than with iron intake alone.¹⁰

How much vitamin A do you need per day?

Vitamin A and its precursors, regardless of the form, cannot be produced by the body itself. This essential micronutrient must therefore be supplied from outside via food. While retinol is only found in animal foods, the precursor of vitamin A, provitamin A carotenoids, is found in plants. However, the bioavailability of the various vitamin A compounds and the conversion rates of the provitamin A carotenoids differ greatly from one another. For this reason, the German Nutrition Society (DGE) specifies so-called retinol activity equivalents (RAE) in its vitamin A intake recommendation. The different properties of the various vitamin A compounds and provitamin A carotenoids were taken into account when calculating these:⁹

Age	*Retinol µg-Activity equivalent/day male**	*Retinol µg-Activity equivalent/day female**
Infants
0 to under 4 months	500	500
4 to under 12 months	400	400
Children and young people
1 to under 4 years	300	300
4 to under 7 years	350	350
7 to under 10 years	450	450
10 to under 13 years	600	600
13 to under 15 years	800	700
15 to under 19 years	950	800
Pregnant women
19 to under 25 years	850	700
25 to under 51 years	850	700
51 to under 65 years	850	700
65 years and older	800	700
Pregnant women		800
Breastfeeding		1300

* Basis for calculation: 1 μg retinol activity equivalent (RAE) = 1 μg retinol = 12 μg β-carotene = 24 μg other provitamin A carotenoids

**Pregnant women and women who wish to conceive should generally avoid vitamin A-containing supplements, as a continuously increased intake can cause birth defects in the child

What are the recommended daily intake limits for vitamin A?

The German Federal Institute for Risk Assessment recommends a maximum daily intake of 0.4 mg of vitamin A. If you are taking multiple dietary supplements containing vitamin A, you should therefore take the precaution of ensuring that the recommended daily intake for any single product does not exceed 0.2 mg of vitamin A.

Important Note on Vitamin A Supplementation

Certain high-risk groups should only take vitamin A supplements after consulting a healthcare professional. These include, among others, people taking medication, those with caffeine sensitivity, heart disease, or diabetes, as well as people with kidney or liver disease. Pregnant women and women planning to become pregnant should generally avoid dietary supplements containing vitamin A, as a prolonged increased intake can cause birth defects in the child.¹⁵

Special dosage recommendations apply to children and adolescents (see table above).

If you are taking multiple supplements, you should add up the nutrients they contain and pay attention to the respective daily limits to avoid an overdose.

Guideline: It makes sense to assess your own health status together with a doctor or naturopath before taking supplements. According to the philosophy of MITOcare founder Christian Burghardt: “Measure, Act, Measure”—supplement in a personalized and targeted manner based on the principle of Causa Logica, rather than buying supplements indiscriminately.

What happens if you overdose on vitamin A?

Unlike water-soluble vitamins, fat-soluble vitamins such as retinol and other vitamin A compounds can be stored in the liver and fatty tissues of the body. This means that while an excess of water-soluble vitamins is simply excreted, too much retinol and co. can potentially be harmful to health. However, a dietary overdose is unlikely and in most cases is due to the intake of vitamin A-containing supplements. Possible consequences can be skin changes or liver damage.¹⁴

How does a vitamin A deficiency develop and how does it manifest itself?

A vitamin A deficiency can be the result of a liver disease that inhibits the storage of this micronutrient. But impaired fat absorption in the intestine can also hinder the absorption of fat-soluble vitamins such as retinol. This can be the case, for example, with chronic diarrhea, celiac disease, short bowel syndrome, Crohn's disease or cystic fibrosis. An early sign of a vitamin A deficiency is night blindness. In severe cases, this can later lead to complete blindness.¹² However, this mainly occurs in developing countries where a healthy, vitamin-rich diet is not guaranteed.¹³

Which foods contain particularly high levels of vitamin A?

Vitamin A is only found in animal products such as liver, eggs, fish and milk. The precursor β-carotene, on the other hand, is found in many fruits and vegetables, such as carrots, kale, pumpkin and mango. As the German Nutrition Society (DGE) reports, it is possible to cover daily requirements through an ovo-lacto-vegetarian diet. This is also possible with a vegan diet, provided there are no restrictions on fat digestion.¹⁶