According to the National Institute of Allergy and Infectious Diseases, 1 billion common colds occur annually in the United States.1 The socioeconomic cost of these noninfluenza viral respiratory tract infections is high, with direct and indirect costs of $40 billion per year.2 While many patients take OTCs for symptomatic management of colds, others use supplements such as high-dose vitamin C, zinc, and Echinacea. Recently, probiotics have also been studied to assess their potential efficacy in combating respiratory diseases, including the common cold.3 Although their mechanism of action is unknown, probiotics might influence immune responses by stimulating antibody production and improving phagocytic activity of leukocytes.
In a recent meta-analysis, the effect of probiotics, specifically Lactobacillus and Bifidobacterium strains, on the duration of respiratory infections was evaluated.3 Twenty trials were included in the meta-analysis: 10 trials on the use of probiotics in children aged 12 months to 12 years, and 10 in adults. One-half of the trials were conducted in western Europe and the remainder in various countries, including two in the United States. The duration of probiotic treatment ranged from 3 weeks to 7 months, with most trials lasting 3 months.
For inclusion into the meta-analysis, the Lactobacillus and Bifidobacterium strains could be administered at any dose; dosage forms included tablets, capsules, and liquids. Lactobacillus strains were studied in 15 trials, 7 of which evaluated the fermented milk drink Actimel, also known as DanActive in the United States. Lactobacillus strains were administered with Bifidobacterium strains in five trials. Using the Cochrane Risk of Bias tool, researchers determined that 12 studies had low risk of bias and that no trials had a high risk.3
Participants receiving a probiotic preparation were reported to have had shorter illness episodes than those taking a placebo, with a half-day to 1-day mean difference in illness duration. Absenteeism was calculated by dividing the number of days absent from day care, school, or work by the number of participants with at least one illness episode.
Twelve trials reported on absenteeism due to respiratory infections or common infectious diseases, of which 11 could be pooled in a meta-analysis. The results suggested fewer days absent compared with days absent among participants taking a placebo.3
The meta-analysis included a large number of high-quality studies that demonstrated a significant benefit from the use of probiotics on the number of days of illness per person. However, heterogeneity was present based on a subgroup analysis of six studies with a low risk of bias; studies had varied durations of illness, probiotic products, and evaluation of absenteeism. Additional studies using different formula-tions and populations are needed.
Treatment of the common cold remains symptomatic, consisting of OTC therapies and selected natural products. Probiotics are generally well tolerated, with only mild gastrointestinal adverse effects. Patients who want to decrease the number of days they are ill with a common cold might benefit from the long-term use of probiotics containing Lactobacillus and Bifidobacterium strains. Unfortunately, a specific recommendation and product are not yet available.