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Vitamin C and the common cold

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For the book by Linus Pauling, see Vitamin C and the Common Cold (book).

The common cold is caused by several strains of viruses including the rhinovirus and the coronavirus. 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.[1] It may be helpful for highly active people training in stressful conditions.[2][3]

The clementine, a citrus fruit, is a good dietary source of vitamin C.

History

In the 1970s, Linus Pauling argued that vitamin C 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.[4] 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.[5]

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.[6] Overall, however, no significant reduction in the risk of developing colds has been observed. 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, but highly physically active people training in stressful conditions (e.g. soldiers training in the Arctic) may benefit from supplementation.[2][3]

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.[7][8][9] 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.[10]

Sources of Vitamin C

Main article: 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.[11] 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.[12]

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.[13] These values are based on maximal absorption with minimal urinary excretion since it is a water soluble 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.[14] Popular vitamin C supplementation products, such as Airborne 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.[15]

See also

References

  1. ^ Kimball, Chad T., ed. (2001). "The common cold". Colds, flu, and other common ailments sourcebook: basic consumer health information about common ailments and injuries. Omnigraphics. pp. 4–9. ISBN 978-0-7808-0435-7. {{cite book}}: |access-date= requires |url= (help)
  2. ^ a b Douglas RM, Hemilä H (2005). "Vitamin C for Preventing and Treating the Common Cold". PLoS Medicine. 2 (6): e168, quiz e217. doi:10.1371/journal.pmed.0020168. PMC 1160577. PMID 15971944. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: unflagged free DOI (link)
  3. ^ a b Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 17636648, please use {{cite journal}} with |pmid=17636648 instead.
  4. ^ "The Difference Between Dr. Linus Pauling's Recommendations and the Linus Pauling Institute's Recommendation for Vitamin C Intake". January 27, 2004. Retrieved November 1, 2010.
  5. ^ Gorton, HC (1999). "The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections". Journal of manipulative and physiological therapeutics. 22 (8): 530–3. doi:10.1016/S0161-4754(99)70005-9. PMID 10543583. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  6. ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 19432914, please use {{cite journal}} with |pmid= 19432914 instead.
  7. ^ Chalmers, TC (1975). "Effects of ascorbic acid on the common cold. An evaluation of the evidence". The American Journal of Medicine. 58 (4): 532–6. doi:10.1016/0002-9343(75)90127-8. PMID 1092164. {{cite journal}}: Unknown parameter |month= ignored (help)
  8. ^ Truswell, AS (11). "Ascorbic Acid". New England Journal of Medicine. 315 (11): 708–710. doi:10.1056/NEJM198609113151113. PMID 3748077. Retrieved 2011-06-13. {{cite journal}}: Check date values in: |date= and |year= / |date= mismatch (help); Unknown parameter |month= ignored (help)
  9. ^ Dykes, MH (1975-03-10). "Ascorbic acid and the common cold. Evaluation of its efficacy and toxicity". JAMA: the Journal of the American Medical Association. 231 (10): 1073–9. doi:10.1001/jama.231.10.1073. PMID 1089817. Retrieved 2011-06-13. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ Brody, Jane E. (April 9, 1998). "Taking Too Much Vitamin C Can Be Dangerous, Study Finds". New York Times. Retrieved 2008-10-19.
  11. ^ GF Ball. Vitamins: their role in the human body. Blackwell Science. pp. 395–415.
  12. ^ D Garriguet (2006). "The effect of supplement on vitamin C intake". Health Reports. 21 (1): 57–62. PMID 20426227. {{cite journal}}: Unknown parameter |month= ignored (help)
  13. ^ Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (2000). Food and Nutrition Board, Institute of Medicine, Washington D.C.; National Academy Press. Published 2000. Accessed 15 May 2011.
  14. ^ GFM Ball (2004). Vitamins in the Human Body. Blackwell Science. pp. 393–415. {{cite book}}: |access-date= requires |url= (help)
  15. ^ "FAQs: How to Use". Retrieved November 1, 2010.
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