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Vitamin C is a water-soluble vitamin found in abundance in foods such as peppers, citrus fruits, broccoli and strawberries. Most animals can synthesize vitamin C endogenously, but humans cannot. Vitamin C is known for its antioxidant properties and ability to fight free radicals. In the 1700s, scurvy was a common problem for sailors on long trips out at sea, causing symptoms such as bleeding gums, poor wound-healing, depression, seizures, and other symptoms leading to death. In 1747, a Scottish Naval surgeon, James Lind, discovered citrus fruits, high in vitamin C, can prevent scurvy.
A meta-analysis reviewed 60+ studies on the effect of vitamin C on the common cold. The six largest studies in the review concluded vitamin C does not help prevent colds in normal adults, but it may help prevent colds in people under acute physical stress. Vitamin C supplementation does have an effect on reducing the duration of colds. In the four largest studies, the duration of colds for subjects was reduced by only 5%, however, two of these studies found a 12 – 41% reduction on school or work absence, which may indicate vitamin C’s ability to reduce symptoms. Three studies showed at least 80% reduction in incidence of pneumonia from people using vitamin C.
A smaller review examined the effect of Vitamin C on patients under acute physical stress. This analysis was on three placebo-controlled studies of skiers, military troops and ultra-marathon runners. Each of the studies found a significant reduction in the incidence of the common cold. A further examination of the study on ultra-marathon runners reported 600mg of vitamin C per day resulted in a 35% decrease in incidence of colds.
Vitamin C and acute respiratory infections
Hemilä H & Douglas RM. , International Journal of Tuberculosis and Lung Disease, 1999
Vitamin C and common cold incidence- a review of studies with subjects under heavy physical stress
Hemilä H., International journal of sports medicine, 1996
Vitamin C supplementation reduces the incidence of postrace symptoms of upper-respiratory-tract infection in ultramarathon runners.
Peters EM, Goetzsche JM, Grobbelaar B, Noakes TD., The American Journal of Clinical Nutrition, 1993
Many Americans do not eat enough fruits and vegetables. The USDA recommends three to five daily servings of vegetables, and two to four servings of fruit. In fact, the 2010 Dietary Guidelines for Americans propose half of your plate at any given meal should be fruits and veggies. Fruits and vegetables are loaded with vitamin C, so if you aren’t eating enough of them, you may want to consider supplementation.
Vitamin C - Health Professional Fact Sheet
Office of Dietary Supplements, National Institutes of Health, 2016