Vitamin A: Everything You Should Know


In this article, we will explain in detail the source of vitamin A, absorption and metabolism, the benefits to the human body, the classification, the foods contained, the intake standards in different populations, the symptoms of vitamin A deficiency and overdose.

What is vitamin A?

Vitamin A is a fat-soluble trace element. The alias is retinol. The discovery of vitamin A dates back to the early 20th century. At that time, people found that in addition to the three major nutrients of carbohydrates, protein and fat, there is another special nutrient that plays a very important role in the health of livestock. Subsequently, scientists have discovered “water-soluble factor B” (derived from cereals) and “fat-soluble factor A” (derived from animal fats), which are named “vitamin B” and “vitamin A”, respectively. Since vitamin A is stored in our body in the form of retinol, vitamin A generally refers to “retinol”.

Vitamin A
Vitamin A

This substance is named retinol because it is found to be the key to synthesizing photosensitizers in visual cells. Vitamin A is closely related to the visual function of humans and animals. Therefore, the common symptoms in the absence are night blindness and vision loss (even leading to total blindness). In addition, vitamin A can help maintain the structure of epithelial cells. It also acts as a growth hormone. Therefore, people who lack vitamin A will also show symptoms such as dry skin and keratinization. For children, the lack of vitamin A will seriously affect the growth and development of the body.

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Vitamin A molecular structure and weight

Molar mass: 286.4516  g/mol

Molecular structure: C20H30O

IUPAC ID: (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraen-1-ol

Density: —

Melting point: 145°F (63°C)

Boiling point: 278.6°F (137°C)


Types and Categories

It mainly includes two forms of vitamin A1 and vitamin A2, and their physiological functions are similar.

Vitamin A1 is mainly found in the liver, blood and the retina of the eyeball, also known as retinol. Its melting point is 64 ° C.

Vitamin A2 is mainly found in freshwater fish. Its melting point is only 17 ~ 19 ° C. The liver, fish eggs, whole milk and eggs of various animals are rich in vitamin A2.

Vitamin A is a fat-soluble vitamin. Also known as fat-soluble vitamins are vitamin D (also known as calciferol), vitamin E (also known as tocopherol) and vitamin K (also known as blood coagulation vitamin). You may check other vitamins introduction in this article “What is vitamin: A, B, C, D, E, and K“.

Vitamin B and vitamin C belong to water-soluble vitamins by the way.


Vitamin A benefits

Vitamin A has many functions, including:

  1. Prevent night blindness and vision loss. It can help treat a variety of eye diseases (vitamin A promotes the formation of photoreceptors in the eye).
  2. Improve the respiratory system’s resistance to infection.
  3. Helps the immune system function properly.
  4. Accelerate the recovery from the variety of diseases.
  5. It can maintain the health of the surface of tissues or organs.
  6. Helps to eliminate senile plaques.
  7. Promotes development strengthens bones and maintains the health of skin, hair, teeth, and gingiva.
  8. External use can help treat acne.
  9. It helps treat emphysema and hyperthyroidism.
  10. It can help treat hair loss.


How much vitamin A do I need to take?

Recommended intake (IU/day)

Age Child Man  Woman Pregnant Breastfeeding
1 to 3 1,000
4 to 8 1,320
9 to 13 2,000
14 to 18 3,000 2,310 2,500 4,000
19+ 3,000 2,310 2,565 4,300



Which foods contain vitamin A?

Vegetable and fruit Meat
  • Carrot (important)
  • Green beans
  • Tomato
  • Asparagus
  • Parsley
  • Red pepper
  • Sweet potato
  • Leek
  • Pea
  • Brussels sprouts
  • Spinach
  • Turnip
  • Broccoli
  • Pumpkin
  • Chard
  • Lentil
  • Melon
  • Papaya
  • Watermelon
  • Grapefruit
  • Apricot
  • Carrot
  • Cow milk
  • Goat milk
  • Egg
  • Cheese
  • Yogurt
  • Liver Paste
  • Chicken
  • Tuna fish
  • Sardine
  • Shrimp
  • Salmon







(You can get more information about what foods contain other vitamins from this article “What are foods that have vitamin A, B, C, D, E, and K?“.)


Vitamin A deficiency

Vitamin A deficiency is a nutritional disorder caused by the lack of such vitamins in the body. The disease is more common in infants and children. Children with vitamin A deficiency first appear night blindness, followed by abnormal systemic keratosis and secondary infection. The reasons are inadequate intake, malabsorption, excessive consumption and metabolic obstruction.

Symptoms of vitamin A deficiency

  • Decreased dark adaptation ability, night blindness occur.
  • Conjunctival dryness and dry eye disease.
  • Pediatric keratoconus softened and perforated lead to blindness.
  • Mucosa and epithelium change.
  • Susceptible to respiratory infections.
  • Taste and smell diminished, appetite decreased.
  • Dry hair, rough skin, keratinization of hair follicles.
  • Poor memory, irritability, and insomnia.
  • Growth and development retardation in children.

If you have the above symptoms, be sure to check the vitamin levels in your blood. Then proceed to the appropriate treatment with the doctor’s advice. Do not blindly purchase vitamin supplements before diagnosis.


Vitamin A overdose (intoxication)

Vitamin A is very important to people. But fat-soluble vitamin A metabolism is too slow in the human body. Therefore, excessive intake of vitamins will be stored in the liver in the form of retinol, which will cause chronic liver damage over a long period of time.

If the dose is too high, it can lead to acute poisoning and even death.

For pregnant women, there is evidence that excessive vitamin A intake in the early stages of pregnancy significantly increases the risk of fetal teratogenesis.

Acute intoxication: A single injection of more than 300000 IU

Chronic intoxication: Long-term excessive intake of vitamin A products.

Symptoms of intoxication

Acute intoxication symptoms Chronic intoxication symptoms
  • Nausea
  • Vomiting
  • Lethargy
  • Diplopia
  • Irritable
  • Cranial nerve spasm
  • Anterior fontanelle expansion
  • Other symptoms of intracranial hypertension
  • Irritability
  • Loss of appetite
  • Low heat
  • Sweating
  • Hair loss
  • Typical bone pain symptoms
  • Metastatic pain
  • Soft tissue swelling
  • Have tender points
  • Short height


Once vitamin A poisoning is diagnosed by the doctor, it should be stopped immediately. Symptoms often disappear within 1 to 2 weeks. But blood vitamin A can maintain a high level within a few months.



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