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Bactericidal skin protein requires vitamin A

Bactericidal skin protein requires vitamin ALack of dietary vitamin A increases the risk of skin infections and acne. Science has known for a long time that creams with synthetic vitamin A can be used against various skin problems, yet they do not know how vitamin A really works. Now, a study conducted by scientists from UT Southwestern Medical Center in Texas, USA, reveals the underlying mechanisms by identifying a bactericidal skin protein that requires vitamin A in order to work. But what kind of vitamin is vitamin A really? When does it work optimally? And is there in fact vitamin A in carrots?

Pure vitamin A, also known as retinol, is a lipid-soluble vitamin that is primarily found in fat-containing animal sources such as liver, oily fish, butter, high-fat cheese, and egg yolk. Vegetable sources such as carrots and spinach do not contain pure vitamin A but a water-soluble precursor called beta-carotene. Pure vitamin A is stored for relatively long time in the liver and fatty tissues. Therefore, we do not need to eat vitamin A on a daily basis. Vitamin A and zinc work closely together, and if you lack one vitamin, it will weaken the other. Vitamin A deficiency is a common problem on a global scale. In countries like Denmark, severe vitamin A deficiency occurs as a result of poor diet habits, alcoholism, and chronic diseases like diabetes.

Vitamin A-dependent protein works like antibiotics

Scientists from UT Southwestern Medical Center in Texas observed that a protein in a molecule from the RELM family (RELMα) works like an antibiotic by killing off bacteria rapidly. They also discovered that this molecule requires vitamin A, regardless if it is found in humans or mice.
According to the researchers, RELMα is the first known example of an antibiotic protein that depends on vitamin A. Their discovery gives an important clue as to how the skin defends itself against infections, and how this defense is regulated by diet.
Our skin is our largest organ, and the skin’s natural microflora is enormous. All these microorganisms keep each other in check a delicate balance, but some of them can cause infection and irritation if they become too dominant. Our skin is the primary meeting point for microorganisms from the surrounding environment, which is why it is vital to have an effective immune defense that works properly at all times. If the skin’s immune defense is broken down, skin infections caused by streptococcus and staphylococcus and other bacteria can easily occur.

Local treatment with vitamin A for skin diseases

Dermatologists use synthetic vitamin A (retinoid) to treat acne, psoriasis, and other skin ailments, but it has long been a mystery how vitamin A works. Now, the scientific experiments carried out on humans and mice prove why vitamin A derivates are effective as treatment against these conditions.
Besides identifying the unique bactericidal properties of the vitamin A-dependent protein, the science team revealed that mice that were given a vitamin A-depleted diet were unable to produce this protein. Because of this, they became increasingly vulnerable to skin infections compared with mice that got plenty of vitamin A from their diets.

Huge therapeutic potential

The scientists understand better now why bacteria and the skin’s natural microflora are important for the development of skin diseases like acne and psoriasis, and they are trying to identify the molecules that are responsible for maintaining a healthy immune defense and a healthy microflora.
In order to study how the skin’s microflora affects our immunity, the scientists used a colony of germ-free mice – which are mice that have been raised in a sterile environment without being exposed to bacteria of any kind. The scientists then identified those genes that are switched on when this type of mouse is exposed to bacteria.
They saw that when the skin is met by bacteria, the skin cells react by producing molecules that help the skin defend itself against infections. The study clearly showed that the diet (including vitamin A) is important for the skin’s ability to defend itself against bacterial infections.
The researchers can see a huge therapeutic potential in their discovery, but more research is needed with regard to inflammatory skin conditions such as acne and psoriasis. Their study is published in Cell Host & Microbe 2019.

Official recommendations and upper safe intake level for vitamin A

The official recommendation for vitamin A in the form of retinol is 800 micrograms (RE = Retinol Equivalents) for adults. The upper safe intake level for vitamin A is 3,000 micrograms/RE, and for post-menopausal women it is 1,500 micrograms/RE for bone health.
Vitamin A supplements should always be taken in combination with a meal, because the fats in food improve the absorption of the nutrient. Overdoses are rarely seen and only occur if the liver stores are saturated and you continue to ingest large quantities of vitamin A (retinol).
Actual poisoning is only seen with ingested amounts that are 100 times or more above the RI (reference intake) level. Pregnant women who ingest over 3,000 micrograms/RE daily have an increased risk of fetal damage and should therefore not consume more than 1,000 micrograms/RE per day.

The skin must primarily be nourished from within.

Vitamin A and zinc

Vitamin A and zinc work closely together, and a deficiency of one nutrient affects the other. Zinc deficiencies appear to be quite common and that may interfere with the effect of vitamin A. Because zinc deficiencies are seen in connection with many skin diseases, zinc supplementation or a diet with more zinc sources may be worth considering.
Our skin is one of the organs that contains the most zinc. This trace element has vital importance for producing and protecting skin cells. Lack of zinc can contribute to acne, eczema, and other skin conditions, according to a study that is published in the science journal Nutrients. Although clinical zinc deficiencies are rare in our part of the world, subclinical zinc deficiency is quite common. Vegetarians and vegans, pregnant and breastfeeding women, and older people are more likely to suffer from this. A large consumption of sugar, calcium, and alcohol plus the use of birth control pills and various types of medication may also increase the risk of zinc deficiency, and this is also the case with certain diseases.

Pure vitamin A from the animal kingdom
Vitamin A precursor from the plant kingdom
Found in animal sources such as cod liver, liver, liver pate, kidneys, butter, cheese, egg yolk and oily fish. Found in green/red/yellow vegetable sources such as carrots, rosehips, parsley, kale, spinach, tomatoes, bell pepper, and melons.
Stored in liver and fat tissue for future use.
Requires zinc to release it from the liver
Stays relatively long in the body
Gets converted into retinol in the intestinal mucosa.
Is not stored in the body.
Particularly powerful antioxidant.
Most powerful form of vitamin A
12 times stronger effect than beta-carotene.
Retinol can be overdosed
Weakest form of vitamin A
The need for this vitamin is correspondingly greater
Not possible to overdose on beta-carotene.


Tamia A. Harris et al. Resistin-like Molecule α Provides Vitamin-A-Dependent Antimicrobial Protection in the Skin. Cell Host & Microbes. 2019

Youichi Ogawa et al. Zinc and Skin Disorders. Nutrients 2018

Daniel Brugger and Wilhelm M. Windisch: Short-Term Subclinical Zink Deficiency in Weaned


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