Get to Know Vitamin C

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Get to Know Vitamin C

Even if you’re not up on your vitamins, you’re probably familiar with vitamin C, especially when cold and flu season rolls around. And you most likely know that citrus fruits are key sources of vitamin C. But there’s more to this vitamin than meets the eye. Curious? Keep reading!

What is vitamin C?

Vitamin C also goes by the name ascorbic acid. It’s a water-soluble vitamin, which means that it dissolves in water, but it’s not well-stored in the body. This means that we need to consume this vitamin every day through food sources or supplements (or both). Vitamin C was discovered in 1928 by Albert Szent-Gyorgyi, a Hungarian biochemist. He isolated a substance from adrenal glands that he called “hexuronic acid,” and in 1933, a man named Norman Haworth deduced the chemical structure of vitamin C, proving that this vitamin was essential and had to be obtained through the diet.

What does vitamin C do?

Vitamin C is needed to make collagen, a protein that plays a role in a number of areas of the body, such as the nervous system, the immune system, bone, cartilage, and blood. Collagen is also needed for wound healing. In addition, vitamin C is an antioxidant, helping to protect cells from damage from free radicals (free radicals are compounds formed when the body converts food into energy; free radicals are also found in cigarette smoke, air pollution, and ultraviolet light from the sun). But besides these well-known functions of vitamin C, other claims have been made about vitamin C and the ability to prevent various types of illnesses.

Vitamin C and illness prevention

Common cold

Vitamin C has long been believed to both fight off and treat the common cold, as suggested by Linus Pauling in the 1970s. However, a 2007 review, which examined placebo (inactive treatment)-controlled trials involving the use of at least 200 milligrams (mg) daily taken continuously to prevent or treat cold symptoms showed no significant decrease in the risk of getting a cold. However, in studies of marathon runners, skiers, and soldiers, vitamin C in doses from 250 mg per day to 1 gram per day reduced cold incidence by 50%. Bottom line? The use of vitamin C supplements might shorten the duration of a cold and decrease severity of symptoms, and it may be particularly helpful in people who do extreme exercise, who live in cold environments, and in populations who may have a low vitamin C status, such as the elderly and chronic smokers. Taking megadoses of vitamin C, however has not shown to be beneficial.

Chronic diseases

Some studies that have followed large groups of people over time have found a protective effect of higher intakes of vitamin C from food or supplements from heart disease and certain types of cancers, but other studies have not, according to the Office of Dietary Supplements (ODS) of the National Institutes of Health (NIH). In terms of cancer prevention, most studies indicate that modest vitamin C supplementation alone or with other nutrients don’t help to prevent cancer or heart disease.

Age-related macular degeneration (AMD) and cataracts

AMD and cataracts are two of the leading causes of vision loss in older adults. But while research doesn’t support the role of vitamin C in preventing AMD, it may help slow AMD progression, along with other antioxidants such as vitamin E, beta-carotene, zinc, and copper. And vitamin C combined with other nutrients in a multivitamin/mineral supplement may help decrease the formation of cataracts, according to one study; however, in the AREDS and AREDS 2 studies, older adults who took vitamin C along with vitamin E and beta-carotene did not have a lower risk of developing or progressing cataracts. On the other hand, a diet rich in fruits and vegetables is link with a decreased risk of cataracts.

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What foods have vitamin C?

Vitamin C is found in many foods, but primarily in fruits and vegetables. Here are some of the top vitamin C-rich foods:

  • Citrus fruits (oranges, grapefruit, lemons, limes)
  • Kiwi
  • Green peppers
  • Broccoli
  • Strawberries
  • Brussels sprouts
  • Cantaloupe
  • Cabbage
  • Cauliflower
  • Tomatoes
  • Potatoes

Vitamin C is also added to some fortified breakfast cereals.

Vitamin C is found in multivitamin/mineral supplements and in supplements that contain only vitamin C. Most supplements contain vitamin C in the form of ascorbic acid, but other forms include sodium ascorbate, calcium ascorbate, ascorbic acid with bioflavonoids, and combination products, such as Ester-C. Ascorbic acid is the preferred source, however.

How much vitamin C do you need?

The Recommended Daily Allowance for vitamin C is:

  • For men 19 years and older: 90 mg
  • For women 19 years and older: 75 mg
  • For pregnancy: 85 mg
  • For lactation: 120 mg

People who smoke need an additional 35 mg of vitamin C each day.

What are signs of vitamin C deficiency?

You might be familiar with the story of sailors who went on long ocean voyages with little or no vitamin C intake. These sailors suffered from and even died from a disease called scurvy. Then, in the mid-1700s, a British Navy surgeon, Sir James Lind, discovered that eating citrus fruits or drinking citrus juice could cure scurvy.

Scurvy is a disease that occurs due to a severe lack of vitamin C, leading to a loss of collagen. Signs of scurvy include:

Scurvy and vitamin C deficiency are rare in developed countries, but they can occur in people with a limited intake of this vitamin. If not treated, scurvy can be fatal. People at risk for vitamin C deficiency include:

  • Smokers and people exposed to secondhand smoke
  • Infants fed evaporated or boiled milk
  • People with a limited variety of food intake: elderly people, people who abuse alcohol or drugs, people with mental illness, people who follow certain fad diets
  • People with intestinal malabsorption
  • Some people with cancer
  • People receiving hemodialysis for end-stage kidney disease

What are signs of vitamin C toxicity?

Vitamin C is generally not toxic at high doses, at least, in healthy adults. That’s because once the body’s tissues become saturated with this vitamin, any excess is excreted in the urine.

However, taking megadoses of vitamin C (usually in amounts greater than 3000 mg daily) may lead to:

  • Diarrhea
  • Nausea
  • Stomach cramps
  • Increased risk of kidney stones in those who have a history of stone formation or who have kidney disease
  • Increased iron absorption and iron overload in people with hemochromatosis, a condition that causes too much iron in the blood

The ODS points out that, under certain conditions, too much vitamin C could act as a “pro-oxidant,” possibly causing oxidative damage (meaning, chromosomal and/or DNA damage), potentially increasing the risk of cancer.

The Tolerable Upper Intake Level (UL) for vitamin C is set at 2,000 mg for adults. Intakes greater than this amount increase the risk of adverse effects. In certain situations, amounts higher than the UL may be given under medical supervision.

Other things to know about vitamin C

Heat and light can destroy vitamin C. Eating fruits and vegetables in their raw form is your best bet for maximizing vitamin C intake. If you’re cooking your produce, use quick-cooking methods that use a minimal amount of water, such as steaming, microwaving, or stir-frying.

If you eat a mostly or all plant-based diet, iron from plant foods isn’t as well absorbed as from animal foods. But you can boost iron absorption from plant foods by eating a food rich in vitamin C with your meals. Skip the orange juice, however, if you have diabetes, unless your blood sugar is low.

If you are receiving chemotherapy or radiation therapy for cancer, realize that vitamin C supplements might interact with these treatments. Make sure you check with your health care provider about taking vitamin C and any other type of antioxidant supplement, especially in high doses.

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Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES on social media

A Registered Dietitian and Certified Diabetes Educator at Good Measures, LLC, where she is a CDE manager for a virtual diabetes program. Campbell is the author of Staying Healthy with Diabetes: Nutrition & Meal Planning, a co-author of 16 Myths of a Diabetic Diet, and has written for  publications including Diabetes Self-Management, Diabetes Spectrum, Clinical Diabetes, the Diabetes Research & Wellness Foundation’s newsletter,, and

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