Vitamin C

Vitamin C, otherwise known as L-ascorbic acid, is a water-soluble vitamin that is irreversibly metabolized. Due to these two factors, it needs to be continually replenished. It is also an essential nutrient – the human body cannot create this nutrient; it must be ingested by eating a varied diet of fresh fruits and vegetables or via supplementation.

There are several well-known functions of vitamin C. As a strong reducing agent, it provides antioxidant defense combating inflammation in the body. It also has a role in improving immune function – it increases the production and function of white blood cells (leukocytes). Eating sufficient quantities of vitamin C, or taking regular supplementation, has been shown to reduce the severity of cold symptoms and shorten time sick. In contrast to common belief, initiating vitamin C supplementation at the start of a cold does not have this effect. Finally, vitamin C is needed for the biosynthesis of neuropeptides (i.e., serotonin and norepinephrine), collagen, and carnitine. It is therefore important for wound healing, energy, and mood.

Recommendations for daily vitamin C intake vary by sex, exposure to environmental toxicants, and other factors. Based on substantial research reviewed by the Linus Pauling Institute, they recommend 400 mg of vitamin C per day for all adults. In contrast, the Institute of Medicine recommends 90 mg/day for men and 75 mg/day for women, which can be satisfied by a single kiwifruit that provides approximately 90 mg of vitamin C. The higher doses recommended by the Linus Pauling Institute are explained in more detail in the sections below.

Vitamin C Levels and Supplementation

Blood levels of vitamin C, called plasma concentration, is regulated by gastointestinal absorption, tissue transport, and kidney reabsorption. These controls can be saturated whereby excess vitamin C is excreted out of the body via urine and feces. Linus Pauling Institute’s research review has found that 200 mg of vitamin C can show approximately 100 percent absorption per meal or supplement. Beyond this, higher doses are not as well absorbed.

One way that these mechanisms can be bypassed is by intravenous (IV) administration. Although this is not recommended for the average person, research has shown that IV vitamin C can significantly improve outcomes from cardiac procedures, which is important for medical professionals to be aware of.

Oral supplements of vitamin C are generally safe; however, at high doses (2 g and above) individuals may experience gastrointestinal symptoms, such as diarrhea, stomach cramping, and nausea. Vitamin C supplements may interact with certain medications. Talk with your doctor before starting any supplementation to avoid interactions. Additionally, if you are susceptible to oxalate kidney stones the Linus Pauling Institute recommends against high-dose supplementation as this may increase stone formation.

Studies on oral supplemental forms of vitamin C have not shown any one form to be more bioavailable than another. Therefore any additional marketing from supplements is not worth the extra cost for consumers.

Eating a varied diet of fruit and vegetables should be sufficient to consume the recommended daily allowance (RDA) of the National Institutes of health. Below is a chart of a select number of foods and their vitamin C content compared to RDA. This is not based-on the Linus Pauling Institute’s recommendation of 400 mg/day of vitamin C. To calculate percent intake by this number, divide number of mg of vitamin C of food product divided by 400mg.

Factors Impacting Vitamin C Status

Vitamin C deficiency results in about 30 days when it is completely removed from the diet of healthy adults. Thankfully, deficiency and resulting disease are not common in the United States.

Severe vitamin C deficiency can be potentially fatal and results in a disease called scurvy. Symptoms of scurvy include bleeding beneath the skin, poor skin healing, easy bruising, hair and tooth loss, and joint pain and swelling (Linus Pauling Institute, 2022).  There have been documented cases of children and elderly who have scurvy in the United States from vitamin C deficiency due to extremely restricted diets.

In addition, individuals who smoke are more likely to be deficient in vitamin C. The general recommendation is for smokers to increase vitamin C intake by at least 35 mg/day more than the average person.

Vitamin C and Health

Vitamin C has been shown to have many beneficial health effects. See the links in the citations to the Linus Pauling Institute and National Institutes of Health webpages to see detailed information on health research related to vitamin C. See the list below for evidence-based findings on the impact of Vitamin C on your health.

Potential Benefits of Vitamin C

• Stimulates production and function of white blood cells.
• With regular supplementation prior to onset, vitamin C reduces cold severity and symptoms.
• Enhances DNA methylation, which has been shown to protect the genome.
• Lowers the risk of stroke, hypertension, and coronary artery disease.
• Reduces the risk of age-related cataracts.

Overview of Vitamin C

Below is an overview of Vitamin C created by the Linus Pauling Institute. For more detailed information, and to read an overview of the current research behind the role of vitamin C in human health, see the links to the Linus Pauling Institute listed.

Citations

Linus Pauling Institute. (2017, December). Vitamin C. Oregon State University. https://lpi.oregonstate.edu/mic/vitamins/vitamin-C

National Institutes of Health. (2021, March). Vitamin C Fact Sheet for Health Professionals. National Institutes of Health Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/vitaminC-HealthProfessional/

Disclaimer

This content is for informational and educational purposes only. It is not intended to provide medical advice or to take the place of medical advice or treatment from a personal physician. All viewers of this content are advised to consult their doctors or qualified health professionals regarding specific health questions. The publisher of this content does not take responsibility for possible health consequences of any person or persons reading or following the information in this educational content. All viewers of this content, especially those taking prescription or over-the-counter medications, should consult their physicians before beginning any nutrition, supplement, exercise or other lifestyle program.