Does Vitamin C Prevent Colds and Flu?

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Vitamin C for preventing and treating the common cold.

* Cochrane Database Syst Rev. 2000;(2):CD000980.

Douglas RM, Hemila H, D'Souza R, Chalker EB, Treacy B.
National Centre for Epidemiology and Population Health, Australia, 2614.

BACKGROUND: The role of oral vitamin C (ascorbic acid) in the prevention and treatment of the common cold has been a subject of controversy for at least sixty years. Public interest in the topic continues to be high and vitamin C continues to be widely sold and used as a preventive and therapeutic agent for this common ailment. OBJECTIVES: To discover whether oral vitamin C in doses of 200 mg or more daily, reduces the incidence, duration or severity of the common cold when used either as continuous prophylaxis or after the onset of cold symptoms. SEARCH STRATEGY: This updated review added to earlier searches, a full search of the following electronic databases: the Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2004); MEDLINE (January 1966 to June 2004); and EMBASE (1990 to June 2004). SELECTION CRITERIA: Papers were excluded if a dose less than 200 mg daily of vitamin C was used; if there was no placebo comparison; if methods of outcome assessment were inadequately described; and if the report did not record any of the three study outcomes (incidence, duration or severity) in sufficient detail to enter into the meta-analysis. Three criteria of study quality were assessed: Jadad scores, placebo distinguish-ability, and allocation concealment. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed trial quality. 'Incidence' of colds during prophylaxis was assessed as the proportion of participants experiencing one or more colds during the study period. 'Duration' was the mean days of illness of cold episodes and 'severity' of these episodes was assessed by days confined indoors, off work or school. or by symptom severity scores. MAIN RESULTS: Twenty-nine trial comparisons involving 11,077 study participants contributed to the meta-analysis on the relative risk (RR) of developing a cold while taking prophylaxis. The pooled RR was 0.96 (95% CI 0.92 to 1.00). A subgroup of six trials that involved a total of 642 marathon runners, skiers, and soldiers on sub-arctic exercises reported a pooled RR of 0.50 (95%CI 0.38 to 0.66).Thirty comparisons that involved 9,676 respiratory episodes contributed to the meta-analysis on common cold duration during prophylaxis . A consistent benefit was observed, representing a reduction in cold duration of 8% (95% CI 3% to 13%) for adult participants and 13.5% (95% CI 5% to 21%) for child participants. Fifteen trial comparisons that involved 7,045 respiratory episodes contributed to the meta-analysis of severity of episodes experienced while on prophylaxis. The pooled results revealed a difference favouring those on vitamin C when days confined to home and off work or school were taken as a measure of severity (p = 0.02), and when restricting to studies which used symptom severity scores (p = 0.16), and for the both measures of severity combined (p = 0.004).Seven trial comparisons that involved 3,294 respiratory episodes contributed to the meta-analysis of cold duration during therapy with vitamin C that was initiated after the onset of cold symptoms, and no significant difference from placebo was seen.Four trial comparisons that involved 2,753 respiratory episodes, contributed to the meta-analysis of cold severity during therapy and no significant difference from placebo was seen.In laboratory studies, differing methods of artificial transmission of virus to vitamin C or placebo treated volunteers in residential experiments gave different results. Volunteers infected by nasal installation showed small or no benefit from vitamin C, whereas a group who were infected more naturally, reported less severe symptom severity scores (p = 0.04). REVIEWERS' CONCLUSIONS: The failure of vitamin C supplementation to reduce the incidence of colds in the normal population indicates that routine mega-dose prophylaxis is not rationally justified for community use. But evidence shows that it could be justified in persons exposed to brief periods of severe physical exercise and/or cold environments. Also, the consistent and statistically significant small benefits on duration and severity for those using regular vitamin C prophylaxis indicates that vitamin C plays some role in respiratory defence mechanisms. The trials in which vitamin C was introduced at the onset of colds as therapy did not show any benefit in doses up to 4 grams daily, but one large trial reported equivocal benefit from an 8 gram therapeutic dose at onset of symptoms.

Can the administration of large doses of vitamin C be of harmful effect?

Pol Merkuriusz Lek (Polish Medical Journal) 2005 Oct;19(112):600-3.
Wroblewski K. Klinika Chorob Wewnetrznych, Nefrologii i Dializoterapii Uniwersyteckiego Szpitala Klinicznego nr 2 w Lodzi.

Vitamin C in its pure form or as a component of multivitamin and combined drugs belongs to the over-the-counter drugs that are available not only at the chemist's but in retail shops as well. Intensive promotion of the advantages of vitamin C as the compound that augments immunity to all sorts of infections, accelerates recovery, eliminates the symptoms of common cold and flu-like diseases, and contributes to general well-being, is of great importance to its intake in quantities far exceeding the recommended dietary allowance. Moreover, the subjects who simultaneously take several anti-common cold drugs are not aware of the fact that almost each of them contains ascorbic acid. Among numerous reports concerning positive effect of vitamin C as antioxidant and free radicals scavenger, there are also those pointing at its potentially pernicious effect. Vitamin C, especially in the doses exceeding daily recommended dietary allowance may result in oxalate crystallization, formation of advanced glycation end products and even exert prooxidant effect.

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Echinacea tea blend shortens duration of cold symptoms

In a double-blind, placebo-controlled clinical study of 95 people, treatment with an echinacea tea preparation (Echinacea Plus®, Traditional Medicinals) early in the course of a cold or flu was significantly more effective in relieving symptoms than a placebo tea. For the 90-day study, participants reported for assignment to one of two treatment groups at the first onset of cold and flu symptoms (scratchy throat, runny nose, fever, etc.). The subjects drank 5 to 6 cups a day of echinacea or placebo tea on the first day of symptoms, reducing the dosage to 1 cup per day for the next five days. Results were assessed with a questionnaire that measured symptom relief, duration of symptoms, and time before subjects noticed a difference in symptoms. The echinacea tea was significantly more effective than placebo in all parameters measured. No side effects were reported in either group. Echinacea Plus is a proprietary blend of E. purpurea and E. angustifolia leaves, flowers, and stems, a water soluble dry extract of E. purpurea root, and flavoring herbs. Eater's Digest® (Traditional Medicinals) was selected as the placebo tea because it was not expected to have a significant effect on cold or flu symptoms at the dosages used in this study. Among other herbs, Eater's Digest contains cinnamon, ginger, and peppermint. Lindenmuth GF, Lindenmuth EB.

The efficacy of echinacea compound herbal tea preparation on the severity and duration of upper respiratory and flu symptoms: a randomized, double-blind placebo-controlled study.

This article originally appeared in The Journal of Alternative and Complementary Medicine 2000; 6(4): 327-334.

Nasal irrigation is effective in improving symptoms and the health status of patients with sinus infections.

Clinical study and literature review of nasal irrigation. School of Medicine, University of California San Diego, USA.

OBJECTIVES/HYPOTHESIS: Nasal disease, including chronic rhinosinusitis and allergic rhinitis, is a significant source of morbidity. Nasal irrigation has been used as an adjunctive treatment of sinonasal disease. However, despite an abundance of anecdotal reports, there has been little statistical evidence to support its efficacy. The objective of this study was to determine the efficacy of the use of pulsatile hypertonic saline nasal irrigation in the treatment of sinonasal disease. Study DESIGN: A prospective controlled clinical study. METHODS: Two hundred eleven patients from the University of California, San Diego (San Diego, CA) Nasal Dysfunction Clinic with sinonasal disease (including allergic rhinitis, aging rhinitis, atrophic rhinitis, and postnasal drip) and 20 disease-free control subjects were enrolled. Patients irrigated their nasal cavities using hypertonic saline delivered by a Water Pik device using a commercially available nasal adapter twice daily for 3 to 6 weeks. Patients rated nasal disease-specific symptoms and completed a self-administered quality of well-being questionnaire before intervention and at follow-up. RESULTS: Patients who used nasal irrigation for the treatment of sinonasal disease experienced statistically significant improvements in 23 of the 30 nasal symptoms queried. Improvement was also measured in the global assessment of health status using the Quality of Well-Being scale. CONCLUSIONS: Nasal irrigation is effective in improving symptoms and the health status of patients with sinonasal disease.

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