Evidence for complementary therapies for upper respiratory tract infection

Infection of the upper respiratory tract is a common acute illness and is responsible for a considerable amount of absence from work or school. Infections can be caused by viruses, bacteria or other microscopic organisms affecting the airways in the nose, ears and throat. They are usually mild, self-limiting and harmless, but can be complicated by secondary bacterial infections such as sinusitis and otitis media. No effective treatments exist, but some symptomatic relief can be obtained from decongestants and analgesics. Several forms of complementary and alternative medicine have been investigated for their effects in preventing or treating upper respiratory tract infections.

Herbal medicine

A Cochrane review of the effects of echinacea (Echinacea angustifolia, Echinacea purpurea and Echinacea pallida) in preventing or treating the common cold was published in 1998.¹ It included 16 randomised controlled trials (RCTs) with a total of 3396 patients. Most trials reported results in favour of echinacea preparations for preventing and treating symptoms. However, inconsistencies in the evidence along with methodological weaknesses and suspected publication bias prevented the authors from making clinical recommendations. Two other reviews have reached similarly favourable but cautious verdicts.²,³ Findings from more recently published trials provide support for the efficacy of echinacea in the early treatment of acute symptoms,⁴–7 but not for preventive effects.⁸,⁹ Data from clinical trials suggest that oral echinacea preparations are well tolerated.

Encouraging evidence has been emerging for the herb Andrographis paniculata, for which anti-inflammatory and immunostimulatory activity has been demonstrated in vitro. At least four placebo-controlled, randomised trials have suggested that when taken during the early stages of a cold, extracts of the herb reduce severity and duration of symptoms.¹⁰–13 In a further placebo-controlled, randomised trial, prolonged use of the herb resulted in a lower incidence of colds.¹⁴ Tolerability appeared to be good in all these trials.

A review of controlled trials of Chinese herbs included 10 relating to upper respiratory tract infections.¹⁵ Most trials reported superiority over antibiotics but, according to reviewers, poor methodological quality rendered the evidence unconvincing. Few trials provided any data on the safety of these herbs.

There is little evidence for other herbs. A placebo-controlled, randomised trial with 227 men and women given an influenza vaccine, reported that Panax ginseng taken for 12 weeks increased immune activity and reduced the frequency of colds and influenza.¹⁶ Steam inhalation of German chamomile (Matricaria recutita) was reported to reduce common cold symptoms in a dose-dependent manner in a placebo-controlled trial,¹⁷ while a mistletoe preparation given subcutaneously for 12 weeks showed a non-significant trend towards reduced frequency and duration of common colds in a small, placebo-controlled, randomised trial.¹⁸

Homoeopathy

A Cochrane review has been published on the efficacy of homoeopathic Oscillococcinum for preventing and treating influenza-like syndromes.¹⁹ Based on the results of three randomised, placebo-controlled prevention trials (n = 2265) the relative risk of developing influenza-like syndrome was 0.64 [95% confidence interval (CI) 0.28, 1.43] which was not statistically significant. The data from four randomised, placebo-controlled treatment trials (n = 1194) indicated several outcomes in favour of the homoeopathic intervention. Time taken to recover was reduced by 0.26 days (95% CI 0.47, 0.05) from a control mean of 4.9 days and return to work was reduced by 0.49 days (95% CI 0.89, 0.08) from a control mean of 4.1. The authors concluded that although the evidence was not strong enough for general recommendations, homoeopathic Oscillococcinum probably reduces the duration of illness but does not prevent influenza-like syndrome. Randomised trials of other homoeopathic preparations have suggested that they perform at least as well as aspirin (acetylsalicylic acid) on measures of symptom severity and absence from work.²⁰,²¹ Placebo-controlled trials have produced conflicting findings.²²,²³

Supplements

A Cochrane review was published in 1997 of the efficacy of high-dose vitamin C (ascorbic acid) in preventing and treating the common cold.²⁴ Thirty placebo-controlled trials were included with more than 8000 adults and children, reported in 19 papers; nine studies were conducted by the same research group. The prophylactic trials consistently indicated that long-term high-dose (> 1 g) vitamin C does not lower the incidence of colds. Therapeutic trials suggested that taking vitamin C at the onset of a cold was effective in decreasing the duration of symptoms. The size of the effect ranged from –0.07% to 39%, with a weighted mean difference of 8–9%. This represented approximately a reduction of half a day per episode of sickness. The methodological quality of trials was variable, with larger effects derived from less rigorous trials. Some trials also suggested that vitamin C reduced the severity as well as duration of symptoms. No clear differences were demonstrated with varying regimes or doses and no adverse effects of high-dose vitamin C were reported.

A Cochrane review of the efficacy of zinc supplements for treating the common cold included seven placebo-controlled, randomised trials with a total of 754 patients.²⁵ The majority of trials were of moderate to good methodological rigor. Although the results of two studies suggested that zinc lozenges reduced the duration and severity of symptoms, the bulk of the evidence did not favour zinc over placebo. Coupled with the adverse effects reported for zinc lozenges in most trials, the reviewers were unable to recommend zinc as a treatment for the common cold. Two other systematic reviews of the evidence reached similar conclusions²⁶,²⁷ and negative findings were reported from a subsequent RCT involving 249 children.²⁸ However, another trial of 50 adults reported a shorter duration of colds with zinc than placebo.²⁹ In a recent placebo-controlled trial with 213 patients, zinc nasal gel shortened the duration of symptoms by more than 6 days.³⁰ However, in a further trial of 160 patients, zinc nasal spray did not reduce symptoms compared with an isotonic placebo spray.³¹

The preventative effect of mineral and vitamin supplementation was tested in a 2-year, placebo-controlled, randomised trial with 725 elderly institutionalised men and women.³² A lower incidence of respiratory tract infections was reported for trace elements (zinc and selenium) compared with placebo, but not for vitamins (β-carotene, vitamin C and vitamin E).

Exercise

Although not a complementary therapy in this context, exercise is worth mentioning because of its potential role in preventing upper respiratory tract infections. Epidemiological studies have identified a J-shaped curve for the relationship between intensity and volume of physical activity and risk of infection. Regular exercise of moderate intensity is associated with a low risk of upper respiratory tract infections, while there is a moderate risk with inactivity and increased risk with the frequent and high intensity exercise of athletes in training.³³ Randomised trials have also demonstrated that adopting a programme of regular moderate exercise (brisk walking) results in fewer³⁴ or shorter duration of symptoms.³⁵,³⁶

Conclusion

Given the difficulty in treating upper respiratory tract infections by conventional means, it is not surprising that there is little evidence that any complementary therapy offers effective relief. The evidence for echinacea is by no means as favourable as its reputation, but is nonetheless encouraging. Another herb, Andrographis paniculata, may offer symptomatic relief. High-dose vitamin C may shorten the duration of a cold. For prevention, there is some evidence in support of echinacea and engaging in regular exercise reduces the risk of infection.

References

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