Vitamin C: Most important vitamin in the human body


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


What is vitamin C?

Vitamin C is an essential nutrient for the body. It is also known as ascorbic acid and L-ascorbic acid. In the human body, vitamin C is an antioxidant that protects the body from the threat of free radicals. Vitamin C is also a coenzyme. Its food source is all kinds of fresh fruits and vegetables. The main effects of vitamin C are as follows:

  • Participate in the hydroxylation reaction.
  • Enhance body immunity and prevent colds.
  • Clean free radicals.
  • Enhance collagen synthesis.
  • Promote hydroxylation of steroids.
  • Prevent cancer.
  • Promote hydroxylation and detoxification of organic matter or poisons.
  • Strengthen the synthesis of neurotransmitters (serotonin and norepinephrine).
  • Participate in antibody formation.
  • Promote the absorption of iron.
Vitamin C: Most important vitamin in the human body
Vitamin C: Most important vitamin in the human body

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Vitamin C absorption, metabolism, and excretion

The first half of the small intestine (duodenum and jejunum) is responsible for absorbing vitamin C. The stomach and oral mucosa absorb only a small part of it.

The vitamin C absorbed by the small intestine is transported to the blood through the portal vein and hepatic vein, and send it to various parts of the body.

When people take vitamin C, the pituitary gland and kidney have the highest concentration of vitamin C, followed by the eyeball, brain, liver, and spleen. When the total amount of vitamin C stored in the body is less than 300 mg, there is a risk of scurvy. The maximum storage capacity of the human body is 2000 mg.

The absorption rate of the small intestine varies depending on the amount of vitamin C intake. When the intake is 30-60 mg, the absorption rate can reach 100%. When the intake is 90 mg, the absorption rate is reduced to about 80%. The vitamin C intake is 1500mg, it is reduced to 49%. When the intake was 3000 mg, it was reduced to 36%. When the intake was 12,000 mg, it was reduced to 16%. This means that the small intestine has a sense of self-protection and protects the body from vitamin C poisoning by its own ability.

There is no clear scientific explanation for the metabolic process and conversion of vitamin C in the body. However, it can be determined that the last metabolite of vitamin C is excreted in the urine.

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Vitamin C molecular structure and weight

Molar mass: 176.13   g/mol

Molecular structure: C6H8O6

IUPAC ID: (5R)-[(1S)-1,2-Dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)-one

Density: 1.65 g/cm³

Melting point: 374°F (190°C)

Boiling point: 1,027°F (553°C)

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Types and categories

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

Vitamin A(also known as retinol), vitamin D (also known as calciferol), vitamin E (also known as tocopherol) and vitamin K (also known as blood coagulation vitamin) belong to the fat-soluble vitamin.

You may check other vitamins introduction in this article “What is vitamin: A, B, C, D, E, and K“.

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Vitamin C benefits

It is the most widely used vitamin in daily life. Because its health benefits are the most excavated, there are quite a few related products on the market.

  • Enhance the body’s resistance to disease and prevent colds.
  • Promote the biosynthesis of collagen, which is beneficial to the faster healing of tissue wounds. When vitamin C is deficient, collagen synthesis is impeded, leading to scurvy.
  • Prevent joint pain, low back pain.
  • Promotes the growth of teeth and bones and prevents gum bleeding.
  • Promotes the metabolism of tyrosine and tryptophan in amino acids and prolongs the life of the body.
  • Enhance the body’s ability to resist stress and immunity to the external environment.
  • Improve the use of iron, calcium and folic acid. Improve the metabolism of fats and lipids, especially cholesterol, and prevent cardiovascular disease.
  • Prevent anemia. Vitamin C converts ferric (Fe3+), which is difficult to absorb, into ferrous (Fe2+) iron that is easily absorbed, thereby promoting iron absorption in the small intestine.
  • Promotes hydroxylation of steroids. Patients with high cholesterol should be given a sufficient amount of vitamin C.
  • Vitamin C can reduce the melanin pigmentation of the skin. Reduces dark spots and freckles, making the skin whiter.
  • prevent cancer. Many studies have shown that it can block the synthesis of carcinogen N-nitroso compounds and prevent cancer.

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How much vitamin C do I need to take?

Daily intake recommended by the doctor as follows. (mg/day)

Ages Child      Man        Woman   Pregnant Breast
0-6 month 40*
7-12 month 50*
1 to 3 15
4 to 8 25
9 to 13 45
14 to 18 75 65
19+ 90 75 80-85 115-120

*AI: Adequate intake also under doctor construction

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What are vitamin C foods?

The main food source of vitamin C is fresh vegetables and fruits. A small amount of vitamin C is also contained in the internal organs of animals.

  • Per 100gr contains more than 100 mg of vitamin C: fresh dates, sea buckthorn, kiwi, grapefruit.
  • Per 100gr contains 50 to 100 mg of vitamin C: green pepper, longan, tomato, strawberry, cabbage, cucumber, citrus, cauliflower.
  • Foods per 100gr contain 30 to 50 mg of vitamin C: cabbage, rape, parsley, spinach, celery, leeks, vegetable moss, peas, kidney beans, radish.

(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?“.)

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Vitamin C deficiency

When the human body lacks sufficient intake of vitamin C for a long time, it causes the most famous disease: scurvy. As early as the 16th century, it has been observed that this deficiency mainly occurs between sailors in the voyage of fruits and vegetables. Initially manifested as fatigue, burnout, swollen gums, bleeding, slow wound healing, etc., even in severe cases of visceral bleeding and death.

Mass vitamin C deficiency is rare but still occurs in infants and the elderly. Scurvy is rare in adults. But people who restrict their diet or avoid fruits and vegetables for a long time also lead to vitamin C deficiency.


  • Insufficient intake
  • Increased demand
  • Physical absorption disorder
  • Drug impact
  • alcoholism
  • Dietetic picky, single types of foods


Although the human body can not synthesize vitamin C, after intake of exogenous vitamin C, can maintain a certain amount of storage in the body. Because of this storage function, even a lack of vitamin C intake can take some time to develop vitamin C deficiency symptoms.

  • General symptoms: Facial paleness, fatigue, loss of appetite, depression, low fever, diarrhea, weight loss.
  • Hemorrhage symptoms: Purpura, ecchymosis, bleeding gingiva, occasional hematuria, shock.
  • Anemia symptoms: Facial pale, orthostatic dizziness.
  • Skeleton symptoms: Joint pain, the pediatric skeletal development disorder.
  • Other symptoms: Edema, fever, poor wound healing, decreased immunity, easy infection.

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Vitamin C overdose (intoxication)

The daily intake of adults is 100 mg. The dosage of the drug is 50-500 mg per tablet, and the therapeutic amount is 150-600 mg per day.

(Children & Adults)
Tolerable Upper Intake Levels (UL) of Vitamin C
1-3 years 400 mg/day
4-8 years 650 mg/day
9-13 years 1,200 mg/day
14-18 years 1,800 mg/day
19 years and up 2,000 mg/day


Symptoms of overdose

Taking 1 to 4 g daily can cause diarrhea, rash, increased stomach acid, stomach reflux, and vomiting. Sometimes urinary stones, urinary oxalate, and urate excretion, deep vein thrombosis, intravascular hemolysis or coagulation may occur. Excessive use may also result in decreased white blood cell phagocytosis. 

When the daily dosage exceeds 5g, it can cause hemolysis, and the severe one can be fatal. When a pregnant woman takes a large dose, it may cause scurvy in infants.

If these symptoms of vitamin overdose or deficiency occur in the body, be sure to go to the hospital for a diagnosis and get the best treatment at the doctor’s suggestion.

You may check other vitamins introduction in this article “What is vitamin: A, B, C, D, E, and K“.

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  • “Chemistry of ascorbic acid” searching result in google. address

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  • Written by Merhaba, MD (Pediatrician)
  • Medically reviewed by Nurmemet, MD (Emergency Medicine Specialist)


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