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What is Vitamin C?
Vitamin C is a water-soluble nutrient. It is naturally present in some foods and added (through fortification) to others. It is also available as a dietary supplement.
As humans, we cannot create vitamin C in the body. Most animals can synthesize the vitamin, but for humans it is an essential dietary component.
Does Vitamin C go by other names?
L-ascorbic acid, ascorbic acid, or ascorbate are other names that identify vitamin C.
What does the body use Vitamin C for?
The body uses vitamin C for many important functions, including:
Creation of collagen (collagen biosynthesis)
Neurotransmitter health
Protein metabolism
Antioxidant properties
Regenerates other antioxidants in the body, such as vitamin E
Immune function
Increases the absorption of nonheme iron (the kind found in plant-based foods)
Collagen Biosynthesis
While Vitamin C is known for its significant role in immunity, it is also required for collagen. Collagen is an essential component of connective tissue -- basically the glue that holds the body together. The component collagen also plays a crucial role in wound healing.
Antioxidant Properties
Vitamin C is also well-known for its function as an antioxidant. Antioxidants are simply compounds that help to mediate the damage effects caused by free radicals, which are basically short-lived and highly-reactive molecules in the body. The nutrient vitamin C performs its antioxidant duties so well that it is thought to even prevent or delay the development of certain types of disease, including:
Cancers
Cardiovascular disease
Other diseases caused by oxidative stress
In addition to being an antioxidant itself, vitamin C is also a nutrient that is a team player. It has been shown to regenerate other antioxidants, further decreasing the damaging effects to the body.
Immune Function
Perhaps its most famous function, vitamin c is key to running an immune system properly. Vitamin C contributes to immunity in the following ways:
Supports cellular functions - A healthy innate and adaptive immune system has a variety of cells and functions, and vitamin C helps to keep things up and running
Supports barrier function - Vitamin C helps fortify the skin and the linings of the body against pathogens and other damaging oxidant activity.
Accumulates in phagocytic cells, such as neutrophils - Phagocytic cells have a special function of ingesting foreign objects such as bacteria or damaged/dying cells. This role of vitamin C helps to decrease the concentration of harmful substances in the body. In other words, vitamin C plays a vital role in killing off the “bad” bacteria (microbes).
Decreases potential tissue damage - Vitamin C is also necessary in the “cleanup” process of an infection site in the body. By helping clear infection sites, this nutrient reduces the chances of tissue damage (necrosis).
As you can “C” (see what I did there), vitamin C is quite essential to a functioning immune system. This function is increasingly supported once you dive into the effects of a vitamin C deficiency.
Recommended Amounts
Dietary Reference Intakes (DRIs)
The recommended daily intake amount for vitamin C depends on age. Intake is based on the Adequate Intake (AI) level for those under one year old. This is the level assumed adequate to meet nutritional needs. An AI is established when there is not enough evidence for a Recommended Dietary Allowance, or RDA.
For children and adults, those one year and older, the recommended daily intake amount is based on the Recommended Dietary Allowance (RDA). This is the amount covering the needs of 97-98% of people in that specific age group or life stage (i.e. pregnancy).
Helpful terms to know
Recommended Dietary Allowance (RDA): covers the needs of 97-98% of individuals in a group; the average amount of a nutrient a healthy person should consume daily. Vary by gender, age, and whether a woman is pregnant or breastfeeding. Developed by the Food and Nutrition Board at the Institutes of Medicine (IOM) of the National Academies.
mg = milligrams
Adequate Intake (AI): recommended daily intake of a nutrient; established by Institute of Medicine (IOM) to meet or to exceed the needed amount to maintain adequate nutrition for most people in a particular stage of life or gender group; established when not enough evidence is available to determine the RDA
Deficiency
Understandably, vitamin C deficiency can lead to some serious symptoms and can make someone more susceptible to infections.
Who is at risk for a vitamin C deficiency?
Certain conditions or lifestyle choices can put you at an increased risk for vitamin C deficiency:
Smokers or those exposed to secondhand smoking
Infants fed evaporated or boiled milk (breast milk is considered an adequate source)
Food insecure individuals
Individuals with a diet that doesn’t regularly include fruits and vegetables
Individuals with chronic, intestinal, or malabsorptive diseases
Pregnant/breastfeeding women
People recovering from surgery
Burn victims
Signs & Symptoms
Common signs and symptoms of an untreated vitamin C deficiency include:
Impaired immunity
Higher susceptibility to infection
Scurvy
An acute (short-term) deficiency of vitamin C leads to scurvy. Symptoms and signs can begin to appear within one month of decreased intake (considered below 10 mg/day) and depleted body stores.
Signs and symptoms of acute deficiency include:
Fatigue
Malaise (weakness)
Gum inflammation
Signs and symptoms of prolonged and progressive deficiency include:
Impaired collagen synthesis (weak connective tissues)
Discolored skin from bruising or bleeding underneath that may appear to look like a rash (i.e. petechiae, ecchymoses, purpura)
Joint pain
Poor wound healing
Skin irritation (hyperkeratosis)
Corkscrew hairs
Depression
Swollen, bleeding gums
Loss of teeth due to capillary fragility
Iron deficiency anemia due to prolonged bleeding and decreased nonheme iron absorption
Bone disease (children)
Historically, sailors who went on long voyages with little or no access to fresh fruits and vegetables developed scurvy. Even before ascorbic acid was proven to be the component active against scurvy, Navy surgeon Sir James Lind determined that citrus fruits and their juices could cure scurvy.
Today, luckily, in developed and undeveloped countries vitamin C deficiency is rare. In many communities, limited food variety is the main risk for this deficiency.
Toxicity
“Mega-dosing” with vitamin C does not mean increased immunity. In other words, high levels of vitamin C intake does not equal high absorption of vitamin C. In fact, studies show that absorption of vitamin C can decrease to less than 50% when taking amounts greater than 1000 mg (that is even less than the upper limit for most adolescents and adults). This is just another reason why staying within the suggested limits and trying to get vitamin C from foods first is a good idea.
High intakes may also contribute to the formation of kidney stones, although the exact role of vitamin C in this process is unclear given the current research available. Long term use of oral vitamin C at a high dose (over 2,000 mg/day) significantly increases the risk of side effects.
Signs & Symptoms
Vitamin C has a low risk of toxicity and has not been known for causing adverse effects. However, it is advised to avoid high intake levels due to common complaints that come along with unabsorbed vitamin C:
Diarrhea
Nausea
Abdominal cramps/bloating
Gastrointestinal (GI) discomfort/disturbances
Headache
Fatigue
Sleepiness or insomnia
Skin flushing
Interactions
High vitamin C levels have been shown to reduce vitamin B12 and copper levels. They also accelerate the metabolism and excretion of existing vitamin C in the body and erode dental enamel.
Other Risks
Increased levels of uric acid, which is a risk factor for gout, can occur with excessive Vitamin C intake. In rare cases, high levels of vitamin C can also cause allergic responses.
Helpful terms to know
Upper Limit (UL): also known as the Tolerable upper intake level; largest daily intake of a nutrient that is considered safe for most people; exceeding this limit is not recommended and may cause harm to the body; Set by the Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine.
Special Populations
Those with the following conditions should especially avoid high-dose or intravenous (IV) vitamin C:
Kidney disease
Hereditary conditions (i.e. hemochromatosis, glucose 6-phosphate dehydrogenase deficiency)
How To Determine Vitamin C levels
Vitamin C status is affected in states of infection or injury. Low levels have been linked to disease. Decrease in vitamin C is accelerated during illness due to the increased level of turnover in the body.
An individual's vitamin C status is typically assessed by measuring:
Plasma vitamin C levels
Other:
Leukocyte vitamin C concentration - may be more accurate indicator of tissue levels; more difficult to assess and not always reliable
These tests should be run under direct medical supervision. Ask your doctor and dietitian for more information.
Due to some of the limitations of these tests, multiple exams and clinical tests should be performed in order to establish a true deficiency. Home-testing kits are available, but I do not recommend them, unless directed so by a licensed medical expert. They are often expensive and less accurate than the tests performed by a doctor or registered dietitian.
Interactions
Be sure to tell your physician about oral supplements you are taking that contain vitamin C. These can produce or interfere with medical test results (i.e. stool tests for occult blood, glucose screening tests).
Other possible interactions between vitamin c include:
Aluminum- may increase aluminum absorption and create kidney problems)
Chemotherapy- may reduce effect of chemotherapy drugs
Estrogen- may increase levels when taken with hormone replacements or oral contraceptives
Protease inhibitors - may reduce the effect of antiviral drugs
Statins and niacin- may reduce effectiveness of these drugs that benefits people with high cholesterol
Warfarin (Jantoven) - high doses of vitamin C can reduce response to this drug (anticoagulant)
Sources of Vitamin C
Fruits and vegetables make the best sources of vitamin C.
How stable is vitamin C?
Vitamin C is considered relatively unstable. Ascorbic acid is water soluble and destroyed by heat, making it susceptible to instability during storage and cooking.
Steaming foods with vitamin C or simply eating them in their raw form can decrease cooking losses.
Supplementation & Treatment with Vitamin C
Uses & Treatment
Infections and inflammation can have an intense impact on Vitamin C levels. Infections drive up both the inflammatory response and metabolic requirements of the body. This makes the required doses of vitamin C needed significantly higher in order to compensate.
Cancer
A recent study reported the following on vitamin C status in cancer patients:
“A significant number of patients with cancer had inadequate plasma ascorbate concentrations. Low plasma status was more prevalent in patients undergoing cancer therapy. Ascorbate status was higher in women than in men, and exercising patients had higher levels than sedentary patients. Our study may prompt increased vigilance of ascorbate status in cancer patients.”
Vitamin C has also been shown at high levels to reduce the effectiveness of chemotherapy. It is important to understand all options and consider the risks and benefits of different therapies before deciding which options to pursue.
Supplementation
Supplementation is thought to aid in the prevention of chronic disease, specifically through the powerful properties of antioxidants.
Preventing or Correcting a Vitamin C Deficiency
Luckily, supplementation has been shown to both treat and prevent infections, particularly those of a respiratory or systemic nature. Prevention of infection requires consistent dietary vitamin C intake that meets established adequate levels.
If I take vitamin C while I have a common cold, will it help me get over the infection quickly?
Vitamin C is preventative in nature, meaning it won’t have a significant effect on the cold you currently have. However, it could affect your ability to fight off infections in the future and even shorten the duration of symptoms. Studies show that the effects seem to be dose dependent.
In other words, regularly meeting your vitamin C requirements each day, not overdosing when you see symptoms, is the best way to increase your immune health. Try getting your vitamin C from food sources first, and then ask your healthcare team or a dietitian familiar with your medical history about supplementing with vitamin C in the case that your needs are not being met through food.
Intravenous (IV) Vitamin C
Vitamin C is sometimes administered in medically monitored settings through an IV. This should only be done under the proper supervision and as part of a protocol established for improving quality of life or qualified clinical studies. Close monitoring must be involved in these situations in the case that negative side effects occur.
Other Forms of Supplementation
Vitamin C can also be supplemented in the form of capsules, oral supplements, or chewable tablets. Again, physician and dietitian recommended guidelines should be followed, as well as directions on the label for correct use.
The Bottom Line
Vitamin C is an impressive nutrient -- playing crucial roles not only in collagen synthesis and immunity, but also in helping the human body get the most out of other nutrients (i.e. vitamin E, nonheme iron). Although it is generally considered safe as a supplement, excessive levels of vitamin C can cause decreased absorption in the body along with gastrointestinal distress.
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References
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Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017; 9(11):1211. https://doi.org/10.3390/nu9111211
Hart J. Eat Pretty. Chronicle Books. 2014. ISBN 978-1-4521-2366-0.
Hemilä H. Vitamin C and Infections. Nutrients. 2017 Apr; 9(4): 339. doi: 10.3390/nu9040339
Heriansyah T, Chomsy IN, Kumboyono K, Pratiwi PA, Wihastuti TA. Expression of Hypoxia-Inducible Factor-1α (HIF1A) and Lp-PLA2 in Low, Intermediate, and High Cardiovascular Disease Risk Population. Vasc Health Risk Manag. 2020;16:507-513. doi: 10.2147/VHRM.S283367
Mayo Clinic Staff. Vitamin C. Mayoclinic.org. Published November 17, 2020. https://www.mayoclinic.org/drugs-supplements-vitamin-c/art-20363932
Office of Dietary Supplements. Nutrient Recommendations: Dietary Reference Intakes (DRI). National Institutes of Health. 2021.
Office of Dietary Supplements (ODS). Vitamin C (Fact Sheet for Health Professionals). Ods.od.nih.gov. Published February 27, 2020. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
Raman R. 7 Impressive Ways Vitamin C Benefits Your Body. Healthline.com. Published February 18, 2020. https://www.healthline.com/nutrition/vitamin-c-benefits
The Nutrition Source. Vitamin C. Hsph.harvard.edu. Published March 2020. https://www.hsph.harvard.edu/nutritionsource/vitamin-c/
U.S. National Library of Medicine. Vitamin C (Also called: Ascorbic acid). Medlineplus.gov. Published September 28, 2020. https://medlineplus.gov/vitaminc.html
White R, Nonis M, Pearson JF, Burgess E, Morrin HR, et al. Low Vitamin C Status in Patients with Cancer Is Associated with Patient and Tumor Characteristics. Nutrients. 2020;12(8):2338; https://doi.org/10.3390/nu12082338