What is vitamin C?
Vitamin C: Overview, Benefits, and Food Sources
Vitamin C, also known as ascorbic acid, is a water-soluble micronutrient found in some foods. It plays several important roles in the body, including:
- Keeping cells safe from free radical damage
- Helping to regulate the body’s natural inflammatory response
- Building collagen, which keeps joints and skin healthy
- Increasing how much iron the body can absorb from food
Not getting enough vitamin C can lead to scurvy, a serious medical condition that causes weakness and bleeding.
Vitamin C: Sources and supplements
Most people get enough vitamin C in their diets. Natural sources of vitamin C include:
- Citrus fruits (oranges, tangerines, grapefruit, pomelo, lime, lemon)
- Red and green peppers
Vitamin C supplements are sold as pills, tablets, and other forms that you take by mouth. Vitamin C is also called ascorbic acid, so supplements may be sold under this name.
Vitamin C supplement dosing
Dosing can vary. But the recommended dose of vitamin C for adults is 75 mg to 90 mg per day based on body size. Children and adolescents usually need less vitamin C than adults each day because of their smaller body sizes.
Some people may need more vitamin C, including those:
- Who are pregnant or breastfeeding
- Smoke cigarettes
- With medical conditions that affect the small bowel
Common uses for vitamin C supplements
Vitamin C supplements are important for people who don’t get enough vitamin C in their diets or who don’t absorb enough vitamin C from their food. This includes people who:
- Have intestinal malabsorption from inflammatory bowel disease
- Are malnourished
- Have limited diets because of food access or medical conditions like autism
Vitamin C supplements may also help:
- Shorten common cold symptoms
- Prevent macular degeneration from getting worse
However, vitamin C supplements do not seem to be effective at preventing:
- Cardiovascular disease
- Macular degeneration
- Viral illnesses
The science behind vitamin C
One of the most popular reasons to use vitamin C is to fight off illnesses and colds. But there’s not a lot of science to support this practice.
Some studies have shown that people who get 200 mg of vitamin C each day may get over colds faster than those who get less vitamin C. But taking vitamin C doesn’t keep you from getting sick in the first place. Taking vitamin C once you get sick doesn’t help you get better faster, either. However, researchers are quick to point out that vitamin C supplements may help on a case-by-case basis when it comes to colds.
Many studies have also looked at whether vitamin C supplements can prevent cancer. However, a couple of large studies didn’t show any benefit.
People who get more vitamin C in their diets are less likely to develop cardiovascular disease. But scientists aren’t sure if this is because of vitamin C or something else in these people’s diets or other habits. Large studies in male participants showed that vitamin C supplements didn’t prevent cardiovascular diseases like strokes.
Finally, research shows that vitamin C supplements don’t prevent macular degeneration or cataracts. But people who already had macular degeneration and took vitamin C supplements had less severe symptoms.
Vitamin C supplement interactions
Like all medications and supplements, vitamin C has a few potential drug interactions. The severity of these interactions depends on how you take the medication (by mouth or as an injection) and your dose.
Vitamin C may interact with:
- Certain attention deficit-hyperactivity disorder (ADHD) medications, like Adderall (amphetamine salts) and Vyvanse (lisdexamfetamine)
- Certain cancer medications, like gemcitabine (Gemzar) and bortezomib (Velcade)
- Aluminum hydroxide
- Copper supplements
- Cyclosporine (Sandimmune)
Estrogen-containing medications, such as certain birth control pills
- Simvastatin (FloLipid, Zocor)
- Warfarin (Coumadin)
Vitamin C supplement side effects
When used at recommended doses, over-the-counter (OTC) vitamin C supplements don’t have many side effects.
But when vitamin C is taken at high doses or is injected into your body by a healthcare professional, side effects are more likely. These include:
- Nausea and vomiting
- Stomach cramps
More serious risks are outlined in the next section.
Safety of vitamin C supplements
High doses of vitamin C can be risky. Adults should never get more than 2,000 mg (2 g) of vitamin C per day from all sources. This includes vitamin C supplements and vitamin C from your diet. Maximum amounts are lower for children, but the specific amount varies by age.
If you take too much vitamin C, it’s possible to develop symptoms like diarrhea, severe nausea, and other stomach-related problems.
A number of people also shouldn’t take vitamin C supplements at all, such as:
- People with thalassemia: Thalassemia is a blood disorder that causes anemia.
- People with glucose-6-phosphate dehydrogenase (G6PD) deficiency: G6PD deficiency is a blood disorder in which red blood cells are broken down more easily.
- People with sickle cell disease: Sickle cell disease is when red blood cells are crescent-shaped, so less oxygen is carried throughout the body.
- People with iron overload: Iron overload (hemochromatosis) is when there’s too much iron in your body.
However, vitamin C supplements are safe for women who are pregnant or nursing.
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Written by Patricia Pinto-Garcia, MD, MPH | Reviewed by Joshua Murdock, PharmD