Supplements Vitamins & Minerals What Is Vitamin C? Can a daily supplement prevent colds and protect your eyes? By Cathy Wong Cathy Wong Facebook Twitter Cathy Wong is a nutritionist and wellness expert. Her work is regularly featured in media such as First For Women, Woman's World, and Natural Health. Learn about our editorial process Updated on December 03, 2021 Medically reviewed Verywell Health articles are reviewed by board-certified physicians and healthcare professionals. These medical reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates. Learn more. by Arno Kroner, DAOM, LAc Medically reviewed by Arno Kroner, DAOM, LAc Facebook LinkedIn Twitter Arno Kroner, DAOM, LAc, is a board-certified acupuncturist, as well as an herbalist and integrative medicine doctor. He operates a private practice in Santa Monica, California. Learn about our Medical Expert Board Print Verywell / Anastasia Tretiak Table of Contents View All Table of Contents Uses Side Effects Dosage Supplementation What to Look For Vitamin C, or ascorbic acid, is an important nutrient found in many foods, such as oranges, red and green peppers, and kiwi. It is also available in supplement form. Vitamin C has many important functions in the body, including: Synthesizing collagen, an important protein Healing wounds Repairing and maintaining cartilage, bones, and teeth Functioning as an antioxidant, meaning it neutralizes free radicals—unstable molecules that can damage cells at the genetic level Historically, vitamin C was used to prevent or treat scurvy, a condition caused by vitamin C deficiency. Today, vitamin C is considered an "immune booster" and is often taken as a cold remedy. There is some evidence that taking it may shorten the length and severity of a cold. This article discusses the uses of vitamin C, possible side effects, and dosage. What Is Vitamin C Used For? Vitamin C has been used to treat and prevent many conditions, including: Asthma, a chronic lung disease Bronchitis, an inflammation of the air passages in the lungs Cancer Cataracts, a condition where the lens of the eye becomes cloudy Chronic or long-term pain The common cold COVID-19 Gastritis, an inflammation of the stomach Glaucoma, a condition of the eyes Heart disease High blood pressure Osteoarthritis, a degenerative disease of the joints Parkinson's disease, a condition of the nervous system There is not much evidence to support most of these uses. There have, however, been a few promising studies. Does Vitamin C Have a Positive or Negative Effect on Arthritis? Vitamin C Deficiency An estimated 8.4% of the U.S. population does not get enough vitamin C. In severe cases, this may lead to scurvy, although the condition is rare in the United States. Symptoms of scurvy include: BruisingBleeding gumsWeaknessFatigueRash Vitamin C deficiency is treated with vitamin C supplements. Some symptoms improve within the first 24 hours of treatment. Others may take a few weeks to go away. In severe cases, the bones may be affected. When this happens, surgery may be needed. 7 Nutrient Deficiencies That Can Make You Sick Common Cold There is mixed evidence for the use of vitamin C to treat or prevent the common cold. A 2016 review found little evidence that daily vitamin C supplements can prevent colds. One exception may be in people whose bodies are under constant physical stress, such as athletes. Studies have, however, found that daily vitamin C supplements may help make colds less severe and decrease their length. Amongst the research: The 2016 review noted that vitamin C taken within the first 24 hours of cold symptoms seemed to shorten how long people were sick.A 2013 study suggested that a daily dose of 1,000 to 2,000 milligrams (mg) of vitamin C can shorten a cold by 8% in adults and 14% in children. Vision Loss Age-related macular degeneration (AMD) is an eye disorder. People with this condition have vision loss. A large 2001 study looked at vitamin C's role in the progression of AMD. Participants received daily vitamin C supplements along with vitamin E, beta-carotene, zinc, and copper. The study concluded that the supplements slowed the progression of AMD by 25%. They also helped slow the loss of visual sharpness and clarity by 15%. Unfortunately, researchers can't be sure that the vitamin C itself made a difference. Since this study, a number of other studies have not found that vitamin C alone is helpful for AMD patients. In addition to this, vitamin C has been studied as a method for preventing certain types of cataracts. A 2014 review found that 135 mg of daily vitamin C may be useful in this regard. This study also found that doses of at least 363 mg could reduce the risk of developing cataracts by 57%. High Blood Pressure Vitamin C has long been used as a treatment for high blood pressure, or hypertension. Unfortunately, research suggests it may not be as helpful as once thought. A 2012 study found that a high dose of vitamin C—around 500 mg daily—produced only small reductions in systolic blood pressure. This is the measurement of your blood pressure during a heart beat. It had minimal effect on diastolic blood pressure, or the measurement between beats. The reason for vitamin C's effect on blood pressure isn't well understood. It is thought that high doses of vitamin C may have a mild diuretic effect. That means it may help reduce water in your body, which can lower blood pressure. Heart Disease and Cancer Research suggests that vitamin C may help prevent heart disease and cancer. Antioxidants like vitamin C do seem to reduce the oxidative stress associated with these diseases. This can happen when there are too many free radicals in your body. A 2013 review found that vitamin C may help prevent stroke. This was mostly true for people who had low intake of vitamin C before treatment or were at high risk for stroke. The review only found this benefit for vitamin C from food sources, not from supplements. A 2013 review noted that high intake of vitamin C does seem to be associated with a lower risk of certain cancers. It also noted that intravenous vitamin C has been shown to improve outcomes for cancer patients. Many experimental cancer therapies include using vitamin C along with other treatments, however. This makes it hard to know how much of an impact vitamin C has on its own. Recap There is some evidence that vitamin C can help shorten the length and severity of a cold. In some people, it may also help prevent stroke and certain cancers. Possible Side Effects Vitamin C is generally considered safe. High doses, though, can cause side effects. These may include: Heartburn Nausea Headaches Stomach cramps Diarrhea Kidney stones Doses over 2,000 mg are considered extreme. These doses may increase the risk of severe diarrhea and kidney stones. You can safely take lower doses of vitamin C during pregnancy. A dose of 85 to 120 mg per day is a common recommendation. Excessive use may cause harm to your unborn baby. Vitamin C can also raise your blood sugar. Use vitamin C with caution if you have diabetes. In older women with diabetes, doses of more than 300 mg daily may increase the risk of death from heart disease. Drug Interactions If you take estrogen or estrogen-based contraceptives, vitamin C may increase the risk of hormonal side effects. This is because vitamin C may slow the rate at which estrogen leaves your body. Vitamin C may also interact with the antipsychotic drug Prolixin (fluphenazine) and reduce the concentration of the drug in your bloodstream. This may make the drug less effective. Vitamin C supplements can also make certain chemotherapy drugs less effective. Let your doctor know if you are taking or planning to take vitamin C with any of these types of medications. Recap When taken in large doses, vitamin C may have side effects. These include stomach problems and headache. Vitamin C may also interact with certain medications. Verywell / Anastasia Tretiak Dosage and Preparation The recommended dietary allowance (RDA) of vitamin C is as follows: Age Daily Vitamin C Dose* 0 to 6 months 40 mg 7 to 12 months 50 mg 1 to 3 years 15 mg 4 and 8 years 25 mg 9 to 13 years 45 mg 14 to 18 years (females) 65 mg 14 to 18 years (males) 75 mg 14 to 18 years (during pregnancy) 80 mg 14 to 18 years (breastfeeding) 115 mg 19 years and over (females) 75 mg 19 years and over (males) 90 mg 19 years and over (during pregnancy) 85 mg 19 years and over (breastfeeding) 120 mg *There are two important caveats to these recommendations: People who smoke should take an additional 35 mg per day.If you've been diagnosed with a vitamin C deficiency, you need to take between 100 to 200 milligrams per day until a blood test shows normal levels of vitamin C. Vitamin supplements are available in the following forms: TabletsCapsulesChewable tabletsGummiesDissolving powders and tablets You may also see different types of vitamin C, including: L-ascorbic acid, typically derived from corn Supplements that combine vitamin C with minerals such as sodium or calcium Citrus bioflavonoids Rose hips No one form is more effective than another. There are also no differences between the effectiveness of the different types of vitamin C. Recap Vitamin C should be taken at the recommended doses. The amount you need depends on your age, sex, whether you are pregnant or breastfeeding, whether or not you smoke, and your current vitamin C levels. Are Vitamin C Supplements Necessary? It is always best to get your nutrients from food rather than supplements. Fruits and vegetables, especially citrus fruits, are good sources. Foods naturally rich in vitamin C include: Raw red peppers: 95 mg per 1/2-cup servingOrange juice: 90 mg per 3/4-cup servingOrange: 70 mg per one medium fruitKiwi: 64 mg per one medium fruitRaw green peppers: 60 mg per 1/2-cup servingCooked broccoli: 51 mg per 1/2-cup servingStrawberries: 49 mg per 1/2-cup servingCooked Brussels sprouts: 48 mg per 1/2-cup servingTomato juice: 33 mg per 1/2-cup servingCantaloupe: 29 mg per 1/2-cup serving If you don't get enough vitamin C from what you eat, a supplement can help get you to the right levels. Recap Taking a daily supplement of vitamin C can help you get the right amount of this nutrient. That said, it is always best to get your vitamins from the foods you eat. What to Look For All supplements should be purchased with caution. You can make sure you're getting a safe, high-quality supplement by choosing products that have been tested and certified by a third party. Look for products certified by an independent certifying body like U.S. Pharmacopeia, ConsumerLab, or NSF International. An ordinary L-ascorbic acid supplement may be a better value than supplements that contain other ingredients. Recap Always look for supplements that have been independently tested for safety and quality. Summary Vitamin C has been used to treat many conditions. It is the best treatment for vitamin C deficiency. It may also help shorten the length and severity of the common cold. Other uses have less conclusive supporting evidence. Food is the best source, but a supplement can help you meet your goals if needed. Speak to your doctor before taking one. The right dosage depends on several factors, and vitamin C can interact with certain drugs. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit 16 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. NIH Office of Dietary Supplements. Vitamin C. Holford P, Carr AC, Zawari M, Vizcaychipi MP. Vitamin C intervention for critical COVID-19: a pragmatic review of the current level of evidence. Life. 2021;11(11):1166. doi:10.3390/life11111166 Quinn J, Gerber B, Fouche R, Kenyon K, Blom Z, Muthukanagaraj P. Effect of high-dose vitamin C infusion in a glucose-6-phosphate dehydrogenase-deficient patient. Case Rep Med. 2017;2017:5202606. doi:10.1155/2017/5202606 Rowe S, Carr AC. Global vitamin C status and prevalence of deficiency: a cause for concern? 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