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Meta-analysis: Elderberry Reduces Upper Respiratory Symptoms


Reviewed: Hawkins J, Baker C, Cherry L, Dunne E. Black elderberry (Sambucus nigra) supplementation effectively treats upper respiratory symptoms: A meta-analysis of randomized, controlled clinical trials. Complement Ther Med. February 2019;42:361-365. doi: 10.1016/j.ctim.2018.12.004.

The common cold and influenza (flu) viruses often cause upper respiratory symptoms such as runny nose, nasal congestion, sore throat, and cough. Over-the-counter medications can help reduce symptoms, and prescription pharmaceuticals may be used in documented cases of flu, but there are concerns about the safety and effectiveness of these drugs for treating viral infections, especially when used in children. Antibiotics may also be prescribed, even though antibiotics are considered ineffective for viral infections, and misuse of antibiotics contributes to antibiotic-resistant pathogens. Elderberry (Sambucus nigra, Adoxaceae) fruit has been used traditionally to treat the common cold and flu. Elderberries contain anthocyanins that have antiviral and immune-stimulating effects. This meta-analysis was conducted to quantify the statistical strength of the relationship (i.e., the effect size) between elderberry supplementation and reduction of upper respiratory symptoms caused by cold and flu infections.

PubMed, Google Scholar, and ScienceDirect databases were searched from inception to September 2018. Search terms included “elderberry,” “sambucus,” “influenza,” “flu,” “respiratory,” “cough,” and “cold.” No limitations were applied to the search. Studies were included if they were randomized, placebo-controlled clinical trials that used elderberry supplementation as the intervention and assessed upper respiratory symptoms as the primary outcome. Trials were excluded if elderberry was combined with another substance or if the primary outcome measures were cytokine production or anti-inflammatory activity.

A total of 137 citations were identified. After screening, four trials met the eligibility criteria and were included in the meta-analysis. The trials were published from 1995 to 2016 and included a total of 180 patients, with 89 in the elderberry groups and 91 in the placebo groups.

In all four studies, upper respiratory symptoms were self-reported. The trials tested “commercially prepared products,” but no additional information was provided about the elderberry products or doses used. Two trials identified laboratory-confirmed flu as the cause of symptoms in patients. One trial evaluated symptoms that were consistent with a diagnosis of flu, and another trial evaluated symptoms that were consistent with the common cold. Two trials excluded patients who had received the flu vaccine, and two trials only excluded patients who had received the vaccine just before the start of the trial. Moderator analysis (i.e., determination if a third variable affects the relation between two other variables) was conducted to determine if the cause of the symptoms (cold versus flu) and flu vaccine status influenced the results.

Elderberry supplementation was associated with a significantly reduced duration of upper respiratory symptoms compared to placebo. The weighted effect size was large (P < 0.001), and heterogeneity was high among the four trials. Moderator analysis found that elderberry supplementation correlated with reduced symptoms caused by both cold flu infections. Elderberry was more effective for reducing symptoms caused by flu (P < 0.001) than for symptoms caused by the common cold (P = 0.087). Moderator analysis found that flu vaccination status did not influence the effects of elderberry supplementation. No publication bias was found, and the risk of bias within studies was rated as low using the Downs and Black checklist.

This meta-analysis provides evidence that elderberry supplementation can reduce the duration and severity of upper respiratory symptoms in people with colds and flu. Elderberry supplementation had a greater effect on symptoms caused by flu than on symptoms caused by colds. The authors point out that this finding should be interpreted with caution because only one of the four trials enrolled people with colds.

According to the authors, future trials should enroll more patients with cold virus infections and involve larger sample sizes. The authors concluded: “These findings present [elderberry preparations as] an alternative to antibiotic misuse for upper respiratory symptoms due to viral infections and a potentially safer alternative to prescription drugs for routine cases of the common cold and influenza.”