What is vitamin C?
Vitamin C is an essential vitamin found in many foods and supplements, and it is important for many bodily functions. It is also referred to as L-ascorbic acid, and it is a water-soluble vitamin excreted through urine. This means that it is not stored in the body, so a daily supply of vitamin C is necessary to maintain optimal health.
Where is vitamin C found?
Vitamin C is abundant in many different fruits and vegetables. Some sources of vitamin C include citrus fruits, and other fruits including kiwifruit, tomatoes, strawberries, and cantaloupe. Potatoes, broccoli, red and green bell peppers, and brussels sprouts are also excellent sources of vitamin C. Enjoying these nutritious fruits and vegetables raw or stir-fried is a good way to maximize vitamin C consumption. The absorption of vitamin C is sometimes reduced with cooking and boiling foods, as it is a water-soluble vitamin that is sensitive to heat.
Vitamin C can also be found in supplements, and the most common supplemental form of vitamin C is ascorbic acid. This is a good choice for vitamin C supplements because it is inexpensive, and because its bioavailability is equivalent to that of naturally-occurring vitamin C found in food. It is also available as sodium ascorbate, calcium ascorbate, and other compounds.
Why is vitamin C important?
Vitamin C is integral to many biological processes. It is an antioxidant vitamin, which means that it neutralizes damaging free radicals in the body. Free radicals are produced in the body as a by-product of metabolism, and they can also increase in number due to many environmental factors, including cigarette smoke, pollutants, and radiation. Neutralizing some of these free radicals helps prevent oxidative stress, which could reduce the risk of its associated conditions such as cardiovascular disease and accelerated aging.
Vitamin C is also essential to the production of collagen, which is a protein that is found in connective tissue.
Vitamin C is also important for the immune system, and it increases the absorption of the iron found in plant foods.
What is the RDA for vitamin C?
The Recommended Dietary Allowance (RDA) for vitamin C is 90 milligrams (mg) daily for men, 75mg daily for women, and 85mg and 120mg daily for pregnant and lactating women, respectively. One interesting thing to note is that cigarette smokers require an additional daily 35mg compared to non-smokers.
The RDA for children is a bit different. The RDA for vitamin C is 40mg for infants under six months, 50mg for infants between seven and twelve months, 15mg for children between one and three years of age, 25mg for children between four and eight years of age, and 45mg for children between nine and thirteen years of age. Most fortified infant formulas contain vitamin C, and breast milk does too as long as the mother consumes adequate amounts of vitamin C.
These values are given by the National Institutes of Health, and the RDA represents the daily intake sufficient to meet the dietary needs of 97-98% of healthy individuals. It is easy to meet the RDA of vitamin C with a diet rich in fruits and vegetables, as either a half cup of red bell pepper or three quarters of a cup of orange juice contains over 100% of the daily RDA for vitamin C.
How much is too much?
The risk of serious toxicity from too much vitamin C is pretty low, as it is a water-soluble vitamin that is not stored in the body for long periods of time like the fat-soluble vitamins. The Upper Limit (UL) given by the National Institutes of Health is 2000mg for adults, 1800mg for adolescents, 1200mg for children between nine and thirteen years of age, 650mg for children between four and eight years of age, and 400mg for children between one and three years of age. The UL represents the maximum daily intake that is unlikely to cause negative health problems.
High intakes of vitamin C significantly above the UL may have side effects including diarrhea, nausea, and stomach cramps. Side effects of megadosing vitamin C are generally quite mild, however it can be harmful in some cases. For example, since vitamin C increases the absorption of plant-based (nonheme) iron, individuals with hemochromatosis should avoid excessive vitamin C consumption as it can increase the risk of iron overload. In addition, vitamin C supplements with large doses of vitamin C could potentially interact with other medications.
What are the benefits of vitamin C?
Some studies show that vitamin C might have certain health benefits. There is evidence to suggest that consuming more fruits and vegetables could help reduce the risk of some cancers. Vitamin C could potentially play a role in this association, because it helps regulate the immune response and reduce the risk of oxidative stress that could potentially lead to cancer. One study of 82,234 women, called the Nurses’ Health Study, found that higher intakes of vitamin C from food were associated with a decreased risk of breast cancer in premenopausal women with a family history of breast cancer. However, it is important to note that this decrease could be due to a variety of factors because it was not an experimental study.
Vitamin C is thought to slow the progression of age-related macular degeneration (AMD). One study called the Age-Related Eye Disease Study found that patients with intermediate AMD taking an antioxidant supplement containing vitamins C, A, E, zinc, and copper had a 28% decreased risk of developing advanced AMD compared to those that did not.
Other evidence suggests that vitamin C can benefit eye health by reducing the risk of cataracts. A cohort study of 30,000 adults found that increased vitamin C intake from food was associated with a lower risk of developing cataracts. However, this same effect was not observed in those taking high-dose vitamin C supplements.
A few studies suggest that vitamin C could help reduce the severity of the common cold. One review showed that vitamin C slightly reduced the duration of colds by 8% in adults and 13.6% in children. This effect was only observed when vitamin C supplements were used prior to the onset of symptoms of the common cold.
Vitamin C deficiency
Vitamin C deficiency is relatively rare nowadays, however some groups are more at risk for vitamin C deficiency than others. Smokers have been shown to have lower vitamin C levels than non-smokers, and this effect could be partially due to the increased oxidative stress from cigarette smoke exposure. People with conditions that cause them to not absorb vitamin C as well are also at risk. These people should make sure that they are consuming adequate vitamin C levels, either through food or supplements.
Another at-risk group for vitamin C deficiency are individuals who have extremely restricted diets, perhaps due to either eating disorders, illicit drug use, or certain fad diets lacking fruits and vegetables.
Vitamin C deficiency, also known as scurvy, can occur within a month of severely restricted vitamin C intake. Scurvy was a condition that was common in 18th century sailors who went on long trips without eating any fresh fruits and vegetables, resulting in a severe lack of vitamin C. The symptoms of scurvy include joint pain, brittle hair, and weak connective tissues due to a lack of collagen production. Scurvy can also result in depression, oral health problems, and iron deficiency anemia due to decreased nonheme iron absorption.
Vitamin C supplementation
Fortunately, vitamin C deficiency can be easily treated by consuming adequate amounts of fruits and vegetables or taking vitamin C supplements. Relief of scurvy symptoms can happen in as little as two days of treatment, and many scurvy patients recover within two weeks.
If you think you are deficient in vitamin C or are at risk for deficiency, consider getting your blood levels tested. As always, consult your doctor before you begin taking any vitamin or mineral supplement, to make sure your medications or health conditions don’t make it a serious risk.
References:
A Randomized, Placebo-Controlled, Clinical Trial of High-Dose Supplementation With Vitamins C and E, Beta Carotene, and Zinc for Age-Related Macular Degeneration and Vision Loss: AREDS Report No. 8. (2001). Arch Opthalmol, 119(10), 1417–1436. doi: 10.1001/archopht.119.10.1417
Douglas, R. M., Hemilia, H., Chalker, E., & Treacy, B. (2007). Vitamin C for Preventing and Treating the Common Cold. Cochrane Database Syst Review, 18(3). doi: 10.1002/14651858.CD000980.pub3
Lobo, V., Patil, A., Phatak, A., & Chandra, N. (2010). Free radicals, antioxidants, and functional foods: impact on human health. Pharmacognosy Review, 4(8), 118–126. doi: 10.4103/0973-7847.70902
Office of Dietary Supplements – Vitamin C. (2020, February 27). Retrieved June 17, 2020, from https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
Scurvy. (2017, September 15). Retrieved June 17, 2020, from https://www.nhs.uk/conditions/scurvy/
Sperduto, R. D., Hu, T. S., & Milton, R. C. (1993). The Linxian Cataract Studies. Two Nutrition Intervention Trials. Arch Ophthalmol, 111(9), 1246–1253. doi: 10.1001/archopht.1993.01090090098027
Vitamin C. (2019, October 23). Retrieved June 17, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK544628/
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Zhang, S., Hunter, D. J., Forman, M. R., et al (1999). Dietary Carotenoids and Vitamins A, C, and E and Risk of Breast Cancer. Journal of the National Cancer Institute, 91(6), 547–556. doi: 10.1093/jnci/91.6.547
