People who consume a diet rich in fruits and vegetables typically have high levels of vitamin C. But low vitamin C levels are associated with certain diseases and conditions, including some cancers and heart disease.

Evidence suggests that dietary supplements of vitamin C can reduce the risk for cataracts and age-related macular degeneration. It can also lower the risk of stroke and protect against some cancers.

Vitamin C Basics

Vitamin C, also known as ascorbic acid, is an essential water-soluble nutrient needed for human growth and development. It is found naturally in many foods and as a dietary supplement. Unlike most animals, humans cannot synthesize vitamin C endogenously and must therefore obtain it through dietary sources. It is best known for its role in immunity and skin care.

Like other antioxidants, it is a nutrient that protects the body’s cells from damage caused by free radicals. Free radicals are unstable molecules that can cause oxidative stress, accelerate aging and contribute to diseases such as cancer, heart disease and arthritis.

While the benefits of consuming plenty of vitamin C are well-known, researchers have yet to pinpoint an optimum amount for optimal health. Some recent studies suggest that high doses of vitamin C might help ward off a common cold, but more research is needed. Vitamin C is a cofactor for a wide range of biosynthetic and gene regulatory enzymes. It is also a powerful non-enzymatic antioxidant in living organisms and can protect indispensable molecules, including proteins, lipids (fats), carbohydrates, and nucleic acids (DNA and RNA) from oxidation. It also participates in redox recycling of other antioxidants, such as vitamin E.[205]

Health Roles

As a water-soluble vitamin, vitamin C is an essential cofactor in many metabolism reactions. It also plays a key role in the immune system, helping to support and strengthen the body's defenses against disease.

It is involved in the formation of certain neurotransmitters, steroid hormones and prostaglandins (hormone-like compounds that regulate blood pressure). Vitamin C also protects indispensable molecules, such as proteins, lipids and carbohydrates, from damage by free radicals produced during normal metabolism or exposure to environmental pollutants and toxins. In addition, it is known to regenerate other antioxidants in the body, including alpha-tocopherol (vitamin E).

Registered dietitian Devon Peart says vitamin C's most well-known health benefits are fighting off colds and improving immune function. But she cautions that taking high doses of the vitamin -- more than 400 mg a day, or more than what's found in 12 to 24 oranges -- may be harmful.

Because humans can't synthesize vitamin C endogenously, they require a daily allowance in the form of foods. A wide range of dietary sources provide enough vitamin C to prevent overt deficiency. However, some groups of people have a greater risk of not obtaining sufficient amounts of the nutrient, including elderly people who live alone; people with limited food variety; those who abuse alcohol or drugs; and those who follow diets that eliminate whole grains and fruits.

Key Benefits

Vitamin C is an antioxidant that donates electrons to decrease levels of reactive oxygen species that can damage proteins, lipids, and DNA. In addition, it plays an important role in collagen synthesis, which is needed for the growth and health of skin, teeth, gums, tendons, and blood vessels. It has also been shown to protect against oxidative stress, and is involved in the production of hormones and metabolic energy.

People who are ill have increased needs for antioxidants, including vitamin C. This is because ill people have more inflammation and thus higher levels of intracellular and extracellular reactive oxygen species. The resulting imbalance of oxidative versus reduced species can lead to a rise in the Sequential Organ Failure Assessment (SOFA) and Acute Physiologic Assessment Chronic Health Evaluation II scores, which are used to estimate organ function and risk of death.

In a series of small randomized controlled trials, vitamin C intake has been shown to reduce the length and severity of the common cold. It may also help protect against eye health and slow the progression of age-related macular degeneration (AMD) and cataracts. It has also been suggested that vitamin C might be beneficial in preventing or treating cancer, but further research is needed to determine whether this benefit exists.