Vitamin C

Figure 1. Chemical structure of Vitamin C.

Vitamin C, also known as Ascorbic Acid, L-Ascorbic Acid, or Ascorbate, is a water-soluble vitamin primarily found in citrus and other fruits and vegetables. Vitamin C is an essential nutrient involved in the repair of tissue, the formation of collagen, and the enzymatic production of certain neurotransmitters, i.e. several hormones and chemical messengers used in the brain and nerves. It is required for the functioning of several enzymes and immune system functions. Vitamin C is also needed to make collagen, a fibrous protein in connective tissue that is weaved throughout various systems in the body including the nervous, immune, bone, cartilage, blood, and other systems, and helps with wound healing.

Vitamin C functions as a cofactor in many enzymatic reactions in the human body that mediate a variety of essential biological functions, including wound healing and collagen synthesis. Another biochemical role of vitamin C is to act as an antioxidant by donating electrons to various enzymatic and non-enzymatic reactions, thereby neutralize free radical molecules which in excessive amounts can damage cells. In plants, vitamin C is a substrate for ascorbate peroxidase. This enzyme utilizes ascorbate to neutralize excess hydrogen peroxide (H₂O₂) by converting it to water (H₂O) and oxygen.

Food Sources

Fruits and vegetables are the best sources of this vitamin.

• Citrus Fruits (Oranges, Kiwis, Lemons, Grapefruit)
• Bell Peppers (Red, Green)
• Strawberries
• Tomatoes
• Cruciferous Vegetables (Broccoli, Brussels Sprouts, Cabbage, Cauliflower)
• Cantaloupe
• White Potatoes
• Green Peas
• Spinach
• Acerola Cherry 
• Bilberry
• Mulberry
• Rose Hip

Taken as a Dietary Supplement

Vitamin C is generally well tolerated. Being a water-soluble vitamin, with dietary excesses not absorbed and excesses in the blood rapidly excreted via urine, Vitamin C exhibits remarkably low acute toxicity. However, because Vitamin C is not well stored inside the human body, it must be taken daily through food or dietary supplements. Vitamin C can be taken orally or via injection.

Vitamin C blood serum levels are considered saturated at levels > 65 μmol/L (1.1 mg/dL), achieved by consuming amounts which are at, or above, the Recommended Dietary Allowance, while adequate levels are defined as ≥ 50 μmol/L. Hypovitaminosis in the case of vitamin C is defined as ≤ 23 μmol/L and deficiency occurs at ≤ 11.4 μmol/L.

The Recommended Dietary Allowance (RDA) for adults 19 years and older is 90 mg daily for men and 75 mg for women. For pregnancy and lactation, the amount increases to 85 mg and 120 mg daily, respectively. Smoking can deplete vitamin C levels in the body, so an additional 35 mg beyond the RDA is suggested for smokers. The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health; for Vitamin C, this is 2000mg daily. Despite this, because the intestines have a limited ability to absorb Vitamin C, studies have shown that absorption of vitamin C decreases to less than 50% when taking amounts greater than 1000mg.

In humans, Vitamin C deficiency may lead to:

• Scurvy. Scurvy is characterized by spots on and bleeding under the skin, spongy gums, 'corkscrew' hair growth, and poor wound healing.
• Impaired Collagen Synthesis, contributing to the more severe symptoms of scurvy.
• Fatigue, malaise.
• Iron-deficiency anaemia due to decreased absorption of non-heme iron.

Overall, Vitamin C distributes readily in high concentrations into immune cells, has antimicrobial and natural killer cell activities, promotes lymphocyte proliferation, and is consumed quickly during infections, effects indicating a prominent role in immune system regulation.

There is some evidence that regular use of supplements may reduce the duration of the common cold, but it does not appear to prevent infection.

Vitamin C affects cells on the inside and outside of the body and its antioxidant properties can be beneficial when it comes to aging, such as a lower likelihood of a wrinkled appearance, dryness of the skin, and an overall better skin-aging appearance.

Side Effects

• Large doses, more than two to three grams, may cause indigestion, particularly when taken on an empty stomach.
• Large doses may cause nausea, abdominal cramps and diarrhoea.
• Large doses may cause gastrointestinal discomfort, flatulence, headache, trouble sleeping, and flushing of the skin.

Background

Vitamin C was discovered in 1912 and isolated in 1928. In 1933, it was the first vitamin to be chemically produced. Vitamin C is listed in the World Health Organization's List of Essential Medicines. Partly for its discovery, Albert Szent-Györgyi and Walter Norman Haworth were awarded the 1937 Nobel Prizes in Physiology and Medicine and Chemistry, respectively.