Deficiency of vitamin A can have a negative physiological effect on the whole organism. We must differentiate between vitamin A₁ (retinol) and vitamin A₂ (retinal). Both forms arise from the beta-carotene plant precursor. Beta carotene belongs to the carotenoid group and is also called provitamin A.
Researchers Stepp, McCollum, and Hopkins realized the importance of the vitamin in 1910 when they raised animals without vitamin A and discovered that they suffered from growth stagnation and conjunctivitis.
The symptoms disappeared when the team fed cod liver oil, butter, and milk to the animals. The German researcher Willhelm Stepp had the idea of this original study. Elmer McCollum isolated the vitamin for the first time three years later.
Research on vitamin A did not begin until the early twentieth century, but the vitamin was used before. In China, they use liver and honey to cure night blindness since 1500 BC. Ancient Egyptians also knew that liver consumption improves crepuscular vision (scotopic vision).
Science has now discovered that vitamin A performs many functions in a person’s body. It is important for the eyes, skin, mucous membranes, growth, immune defense and plays a role in the development of the embryo.
How is vitamin A absorbed and processed by the body?
Your body absorbs one of the two precursors of vitamin A through food. Beta carotene is contained in plant and retinyl sterols in animal sources. Both forms are transformed into retinol in the intestine and liver.
The liver stores retinol as a reserve substance or enters it into the bloodstream.
Retinol is transported to the target tissue through the bloodstream.
There the enzymatic breakdown of retinol into retinoic acid takes place, which is then actively present in the cells.
The kidneys excrete the end products of metabolism through the urine. Foods that contain vitamin A should be consumed with fat. Fat helps extract vitamin from food.
The 5 most important tasks of vitamin A
Vitamin A assumes many tasks in your body.
Below you will find the five most important tasks.
Vitamin A allows night vision
Maintaining eye health is the best-known function of vitamin A, as it is a crucial component of the visual rhodopsin pigment (visual purpura). Rhodopsin is a protein and is found in the retina of the eyes.
In the retinal rods, it is responsible for the light-dark adjustment and the perception of gray tones. It acts as a light sensor and reacts to the smallest changes of light. If the light units (photons) hit the protein, it changes its shape.
As a result, it launches a series of biochemical processes that allow it to see well in the dark. It is also involved in the formation of eye fluid.
Vitamin A is involved in the construction and protection of the skin
Vitamin A regulates skin cell growth, as it actively participates in its construction and protection. Retinoids work in the epidermis (upper layer of skin). Vitamin A regulates the cornification processes of the skin and is also used against acne.
Retinol also plays a role in regulating sebum production and collagen formation. Collagen is found in the lower layers of the skin and ensures that the skin remains soft.
Vitamin A is the basis of growth
Vitamin A can inhibit or promote cell growth. It also has an impact on cell differentiation. In cell differentiation, cells are structurally modified so that they can fulfill their task.
Vitamin A particularly differentiates new skin cells and mucous membranes. It also plays a role in the development and formation of hair, eyes, lymphatic vessels, sex cells, teeth, and bones. A symptom of a vitamin A deficiency is the formation of bone tissue in places where there are normally no bones.
This is due to an incorrect differentiation of the cells.
Vitamin A regulates the immune system
Its effects on the skin and mucous membranes protect it from harmful viruses. The skin and mucous membranes act as barriers so that viruses cannot enter the body.
Vitamin A also participates in the formation and differentiation of white blood cells, whose main task is to avoid pathogens. Vitamin A also affects regulatory T cells.
These prevent excessive immune reactions and, therefore, autoimmune reactions.
Vitamin A plays an important role in reproduction
Since it regulates the formation of the sex hormones: testosterone and estrogen. Testosterone in turn has a positive impact on the quality and number of sperm. Research on this topic has shown that vitamin A deficiency affects sperm production.
Vitamin A also has a regulatory effect on embryonal development. It is involved in the formation of new cells and supports the development of the lungs. Too much vitamin A during pregnancy can cause birth defects.
Therefore, pregnant women should avoid foods that contain a lot of vitamin A.
As you can see, vitamin A is involved in many biochemical processes in the body. Insufficient vitamin supply interferes with these processes and, therefore, damages health.
Symptoms and consequences of a vitamin A deficiency
Vitamin A is considered an eye vitamin, but the symptoms of vitamin A deficiency are not limited to the eyes. As with most deficiency symptoms, nonspecific symptoms appear first.
These include: headache, paleness, dizziness, dullness, and difficulty concentrating.
The cause of these symptoms is anemia. With anemia, the concentration of red blood cells in the blood is too low. Red blood cells carry oxygen from the lungs to the organs. If less oxygen is transported to the organs, this reduces performance.
Vitamin A, therefore, regulates the formation of red blood cells.
Night blindness and reduced vision
The best-known symptom of a vitamin A deficiency is night blindness. It is difficult for those affected to see in low light. In the dark, as in the night, people see nothing at all. This is due to the lack of rhodopsin, which allows a clear and dark vision.
If the vision is altered, the image becomes blurred and cloudy. Because vitamin A is important for the formation of eye fluid, a deficiency can cause the bulbar conjunctiva to dry. This dehydration due to a vitamin A deficiency is known as xerophthalmia and is common in emerging countries.
In addition, there are often visible gray spots, called bitot spots.
Without medical treatment, blindness occurs due to the melting of the cornea (keratomalacia).
A deficiency of vitamin A can lead to growth disorders in children since the vitamin is involved in the formation and differentiation of new cells. It is also essential to build and maintain bones and teeth.
A symptom of deficiency is the formation of bone in places where normally there should be no bones. A deficiency can also lead to altered or delayed lung development.
Skin and mucous membranes
Vitamin A deficiency dries the skin and causes psoriasis. Another symptom is hair loss. A deficiency also favors the development of acne. The lung tissue is also affected.
The cells of the mucous membrane become corneal cells, which can cause respiratory difficulties.
This transformation also affects the mucous membranes of the nose and respiratory tract, which can lead to cell death (necrosis) or pneumonia.
Embryonic development malformations
A deficiency of vitamin A can lead to embryo malformations. The genitals, gastrointestinal tract, teeth, and ears of the embryo are affected.
However, these malformations can also result from excessive consumption of retinol. Retinol is the biologically active form of vitamin A and is only found in animal products.
Therefore, you should avoid this form of the vitamin during pregnancy and take vitamin A in the form of a plant. Beta carotene can be stored in the liver until needed. This cannot lead to an overdose.
Propagation of vitamin A deficiency
Lack of vitamin A is one of the biggest nutritional problems in the world. This is mainly due to the limited supply in developing countries, whose diet is mainly based on rice. Normal rice does not contain vitamin A. As a result, children often go blind in these countries.
According to the development aid organization Christoffel Blindenmission (cbm), between 250,000 and 500,000 children go blind every year due to a vitamin A deficiency.
Other studies assume that 2 million people die from vitamin A deficiency every year. A countermeasure is the development of a genetically modified rice, the so-called golden rice.
Scarcity does not only occur in developing countries. Deficiency symptoms can also occur in industrialized countries.
For example, the Huffington Post reports a 13-year-old boy from Australia who was almost blind due to his poor diet. The child’s diet was low in vitamin A since he lived almost exclusively from fast food.
Who is at risk?
The lack of vitamin A is very dangerous for children, as they are still developing. Children also have a smaller liver and, therefore, can store less vitamin A.
But pregnant women, people over 65, and high-performance athletes also have a greater need. These people need more vitamin A due to physical changes.
Another risk group is vegetarians, vegans, or dieters. They eat less vitamin A because of their diet and should be careful to include foods that contain vitamin A in their diet.
Diseases can prevent or complicate the absorption of vitamin A. These mainly include diseases of the liver and gastrointestinal tract.
People who are overweight or have problems with alcohol often suffer liver problems (fatty liver, liver cirrhosis). This hinders the absorption of vitamin A.
What can you do with a vitamin A deficiency?
Lack of vitamin A is rare in industrialized countries. But if there is a deficiency, it can be dangerous. Therefore, it is important to prevent it.
Prevention with proper nutrition
A varied diet is a basis to prevent many diseases. However, vitamin A is not found in all foods. Vegetarians and vegans in particular, therefore, should pay attention to their diet.
The following foods contain a lot of vitamin A:
- Sweet melon, watermelon, cherries, apricots, mango, papaya.
- Cod liver oil, liver, egg, mackerel, tuna, poultry meat.
The bioavailability of vitamin A increases with the addition of fat. Bioavailability describes the body’s ability to absorb and process a certain nutrient.
Some foods contain fats naturally, which guarantees bioavailability. Others, especially fruits and vegetables, have no fat. Therefore, you should always add some fat, such as oil, to the preparation.
It is also important that the food is well chopped. The bioavailability of vitamin A from chopped carrots is five percent. The carrot puree is 20 percent.
You can chop the carrot well for this or you can chew the carrot for longer. According to the WHO, you should take about 1 mg of vitamin A per day.
Supplements in case of existing deficiency
Taking vitamin A supplements can prevent a deficiency or compensate for an existing deficiency. In the case of very strong symptoms, such as night blindness, you should definitely consult your doctor to avoid major evils. It is also important to find the cause of vitamin A deficiency.
Most vitamin A supplements can be found in capsule form. You can take the capsules with food.