The common cold

Common cold

The common cold is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever...

 is caused by several strains of viruses including the rhinovirus

Rhinovirus

Human rhinoviruses are the most common viral infective agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35 °C , and this may be why it occurs primarily in the nose...

 and the coronavirus

Coronavirus

Coronaviruses are species in the genera of virus belonging to the subfamily Coronavirinae in the family Coronaviridae. Coronaviruses are enveloped viruses with a positive-sense single-stranded RNA genome and a helical symmetry. The genomic size of coronaviruses ranges from approximately 16 to 31...

. Colds are the leading cause of doctor's visits and the number one reason for absences from work and school. However, vitamin C does not prevent the common cold or decrease the severity of symptoms.

History

In the 1970s, Linus Pauling

Linus Pauling

Linus Carl Pauling was an American chemist, biochemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists of the 20th century...

 argued that vitamin C

Vitamin C

Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species. In living organisms ascorbate acts as an antioxidant by protecting the body against oxidative stress...

 could significantly decrease the incidence of the common cold, which spurred a widespread belief that consuming more vitamin C will reduce the risk of catching a cold and reduce its severity. A prospective, controlled study of 715 students in a technical training facility came to a similar conclusion, finding that vitamin C in megadoses administered before or after the appearance of cold and flu symptoms relieved and prevented the symptoms in the test population compared with the control group.

In the past 30 years, numerous placebo-controlled trials have examined the effect of vitamin C supplementation on the prevention and treatment of colds. More than 30 clinical trials with over 10,000 participants have examined the effects of taking daily vitamin C in doses up to 2 g/day. A review of Cochrane, PubMed, Natural Standard, and the National Center for Complementary and Alternative Medicine databases, for example, found that regular vitamin C consumption may reduce the duration of cold symptoms in both adults and children, but it does not decrease the severity of cold symptoms.

Overall, however, no significant reduction in the risk of developing colds has been observed. When observing those individuals who developed the common cold while taking vitamin C, no significant difference in severity of symptoms was noticed within the study overall. Although an extremely small significant reduction in the duration of colds has been reported, the decrease cannot be significantly linked to vitamin C intake. However, in a subgroup of marathon runners, skiers, and soldiers training in the Arctic doses ranging from 250 mg/day to 1 g/day decreased the incidence of colds by 50%. Therefore, the majority of studies of non-athletic people, when looked at collectively, led researchers to conclude that vitamin C does not prevent or treat the common cold.

Criticism

Claims of vitamin C's efficacy in treating the common cold have been criticized by many researchers. The most-cited reviews of the subject have concluded that there are no beneficial effects beyond a placebo. Aside from research showing vitamin C to be ineffectual and unsuccessful against a cold, concerns have also been raised about the dangerous effects vitamin C can have when taken inappropriately.

Sources of Vitamin C

See Sources of Vitamin C.

Generally, nutrients have more bioavailability in naturally occurring food sources. However, ascorbic acid’s bioavailability is as equal in natural sources as it is in supplemental sources. Therefore, while it is better to consume natural foods such as red peppers, oranges, strawberries and grapefruit, because they offer other nutrients that are likely to have a higher bioavailability, it is acceptable to consume vitamin C from a supplement and still maintain adequate intake levels.

Dosage

The recommended daily allowance for vitamin C in the United States is 75 mg per day for women and 90 mg per day for men, but with higher intakes being advised for smokers, pregnancy and breastfeeding. These values are based on maximal absorption with minimal urinary excretion since it is a water soluble

Vitamin

A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...

 vitamin. It has been suggested that taking doses above the RDA may have healthful benefits. Typically 70-90% of vitamin C is absorbed in the body, but when taken in doses higher than 1 g, absorption decreases to 75% and further decreases to merely 16% after a 12 g dose. Popular vitamin C supplementation products, such as Airborne

Airborne (dietary supplement)

Airborne is a dietary supplement containing herbal extracts, amino acids, antioxidants, electrolytes, synthetic vitamins, and other ingredients. It was created by Victoria Knight-McDowell in the early 1990s. It is offered for sale over-the-counter in many U.S. retail stores in three different...

 or Emergen-C, contain much higher doses of vitamins than necessary. Typically these products have 1 g of vitamin C as ascorbic acid, however the directions suggest taking the product up to three times per day. Since the body can only absorb a certain amount of vitamin C in a day, this dosage would flood the body and as research suggests, likely decrease the absorption.