Vitamin C is the only water-soluble vitamin that doesn’t belong to the vitamin B category. It is one of the body’s main antioxidants and is required for collagen synthesis.

Types

Vitamin C comes in two forms, the most common of which is known as ascorbic acid.

An oxidized form of ascorbic acid called dehydroascorbic acid also has vitamin C activity.

Role and Function

Vitamin C supports many essential body functions, including:

• Antioxidant defenses: Your body uses antioxidants to protect itself against oxidative stress. Vitamin C is one of its most important antioxidants.
• Collagen formation: Without vitamin C, the body is unable to synthesize collagen, the main protein in connective tissue. As a result, deficiency affects your skin, tendons, ligaments and bones.
• Immune function: Immune cells contain high levels of vitamin C. During an infection, its levels are quickly depleted.
• Unlike the B vitamins, vitamin C doesn’t act as a coenzyme, although it is a cofactor for prolyl hydroxylase, an enzyme that serves an essential role in the formation of collagen.

Dietary Sources

• The main dietary sources of vitamin C are fruits and vegetables.
• Cooked animal-sourced foods contain virtually no vitamin C, but low amounts can be found in raw liver, eggs, fish roe, meat and fish.
• Cooking or drying foods significantly reduces their vitamin C content.

Recommended Intake

The recommended daily allowance (RDA) of vitamin C is the estimated amount of the vitamin most people need every day.

The below value also shows the tolerable upper limit (UL), which is the highest level of intake thought to be completely safe for most people.

No RDA has been established for infants. Instead, scientists have estimated their adequate intake, which is similar to the RDA, but based on weaker evidence.

RDA (mg/day)      UL (mg/day)

Infants        0–6 months           40*                       –

7–12 months        50*                       –

Children      1–3 years              15                         400

4–8 years              25                         650

9–13 years            45                         1,200

Women       14–18 years                   65                         1,800

19+ years              75                         2,000

Men             14–18 years                   75                         1,800

19+ years              90                          2,000

Pregnancy                               80–85         1                 800–2,000

Lactation                                 115–120               1,800–2,000

*Adequate intake

Deficiency

• Deficiency is rare in Western countries, but may develop in people who follow restrictive diets or eat almost no fruits or vegetables. People with drug addiction or alcoholism are also at greater risk.
• It leads to a disease known as scurvy, which is characterized by the breakdown of connective tissue.
• The first symptoms of deficiency include fatigue and weakness. As scurvy becomes worse, people may experience spotted skin and inflamed gums.
• Advanced scurvy may cause loss of teeth, bleeding gums and skin, joint problems, dry eyes, swelling and impaired wound healing. Like all vitamin deficiencies, scurvy is fatal without treatment.

Side Effects and Toxicity

• Most people tolerate high doses of vitamin C without any side effects.
• However, very high doses exceeding 3 grams per day cause diarrhea, nausea and abdominal cramps. This is because only a limited amount of vitamin C can be absorbed from a single dose.
• Taking high-dose supplements over 1,000 mg per day may also increase the risk of kidney stones in predisposed people.

Benefits of Supplements

• There is mixed evidence that vitamin C supplements benefit people who get adequate amounts from the diet.
• However, vitamin C can improve iron absorption from a meal, helping those who are low or deficient in iron.
• Additionally, one analysis of 29 studies concluded that supplements that provide at least 200 mg of vitamin C per day may help you recover from the common cold.
• While vitamin C supplements may also help lower blood pressure, there is no evidence that they reduce the risk of heart disease.
• Studies also suggest vitamin C may reduce the risk of cognitive decline, improve blood vessel function and reduce blood sugar levels, but high-quality studies are needed before definite conclusions can be reached.

Summary of Vitamin C

• Vitamin C is a powerful antioxidant that’s vital for the maintenance of connective tissue.
• The main dietary sources are fruits and vegetables, but low amounts can be acquired from raw animal-sourced foods. Deficiency, known as scurvy, is rare in developed countries.

Most people tolerate high-dose supplements without any adverse effects. However, studies on the benefits of vitamin C supplements have had mixed results, suggesting supplements may not be that useful for those who already get sufficient amounts from their diets.