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Preventing and Treating Influenza With Natural Medicines

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Vaccinations and antiviral drugs are not the only options available for preventing and treating influenza. This article discusses the scientific evidence that that certain nutrients and herbs may also be useful.


Sambucol, a proprietary preparation that contains extracts of black elderberries (Sambucus nigra L.) and raspberries (Rubus idaeus L.) inhibited the replication of influenza virus in the test tube. In addition, an extract of Sambucus nigra L. decreased the infectivity of human influenza virus H1N1 (the type that causes swine flu) in the test tube.[1] In clinical trials, treatment with Sambucol decreased the duration of illness in people suffering from influenza.

In a double-blind study, 40 patients who had flu-like symptoms during an influenza outbreak were randomly assigned to receive Sambucol or placebo. Children received 30 milliliters (two tablespoons) per day and adults received 60 milliliters (four tablespoons) per day for three days. After two days of treatment, a higher proportion of patients in the Sambucol group than in the placebo group reported significant improvement in symptoms (93 percent vs. 25 percent). Symptoms resolved completely after three days in 87 percent of patients receiving Sambucol and in 33 percent of those receiving placebo.[2]

In another double-blind trial, 60 patients with influenza-like symptoms for 48 hours or less were randomly assigned to receive Sambucol (15 milliliters, four times per day during meals) or placebo for five days. The mean time until symptoms had completely or almost completely resolved was 56 percent shorter in the Sambucol group than in the placebo group (3.1 vs. 7.1 days). No side effects occurred.[3]


Oxidative stress appears to contribute to the lung damage that may result from influenza infection. N-acetylcysteine (NAC) is an antioxidant and is also a precursor to glutathione, which is one of the major antioxidants that occur naturally in lung tissue.

In a double-blind study, 262 mostly elderly individuals were randomly assigned to receive NAC (600 milligrams twice a day) or placebo for six months, beginning in October or November. Compared with placebo, NAC reduced by 43 percent the proportion of subjects who experienced at least one episode of influenza (30 percent vs. 52 percent). The percentage of episodes that were mild was significantly higher in the NAC group than in the placebo group (72 percent vs. 48 percent). The mean time in bed per episode was 61 percent less in the NAC group than in the placebo group. The frequency of laboratory-documented influenza infection was similar in the two groups, but fewer infected subjects in the NAC group than in the placebo group developed symptoms (25 percent vs. 79 percent). During NAC treatment, certain parameters of immune function improved.[4] The results of this study demonstrate that NAC can decrease the frequency and severity of influenza episodes by decreasing the number of infections that cause symptoms.

Vitamin C

Vitamin C has been shown to inactivate influenza virus in test tubes. According to one practitioner, supplementing with massive doses of vitamin C can relieve symptoms and enhance recovery in patients with influenza. Vitamin C was usually given six to 15 times per day in amounts just below the dose that produced diarrhea (i.e., the bowel-tolerance dose). Increasing the frequency of administration increased the amount of vitamin C tolerated. The best results were achieved when patients reached at least 80 to 90 percent of their bowel-tolerance dose. The amount of vitamin C a patient could take without diarrhea increased with increasing disease severity. Some patients were able to tolerate up to 150 grams per day when suffering from influenza, but as they improved, the amount of vitamin C they could tolerate decreased. Symptoms recurred in some cases if bowel-tolerance doses were discontinued before the patient was completely well.[5],[6]

Green and Black Tea

Green tea extract inhibited the growth of influenza virus in the test tube. This effect appeared to be due at least in part to (-)epigallocatechin, one of the major catechin molecules in green tea. In a study of elderly nursing home residents, gargling with a solution of green tea catechins three times per day reduced the incidence of influenza by 87 percent.[7]

In a double-blind trial, 197 adults received capsules providing daily 378 milligrams of green tea catechins and 210 milligrams of theanine (a constituent of black tea) or a placebo for five months, from November to April. The incidence of influenza infection was significantly lower, by 69 percent, in the group receiving the tea compounds than in the placebo group (4.1 percent vs. 13.1 percent).[8]

Vitamin D

Vitamin D plays a role in immune function. It has been suggested that the decline in vitamin D levels that occurs during the winter months might explain the higher incidence of influenza in the winter than at other times.[9] In a double-blind trial, 430 children (mean age 10 years) received 1,200 IU per day of vitamin D or a placebo for 15 to 17 weeks, between December and March. The incidence of laboratory-documented influenza was significantly lower, by 42 percent, in the vitamin D group than in the placebo group (10.8 percent vs. 18.6 percent). The reduction in risk was restricted entirely to children who had not been taking other vitamin D supplements. Among that group, the risk reduction compared with placebo was 64 percent.[10]

However, a more recent study found that taking vitamin D did not decrease the risk of developing flu-like symptoms.[11] Because the results of research are conflicting, the value of vitamin D for preventing the flu remains uncertain.

Note: The information provided in this article is for educational purposes only, and should not be construed as personal medical advice or instruction. No action should be taken based solely on the contents of this article. Readers should consult appropriate health professionals on any matter relating to their health and well-being.

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1 Roschek B Jr, et al. Elderberry flavonoids bind to and prevent H1N1 infection in vitro. Phytochemistry 2009;70:1255-1261.

2 Zakay-Rones Z, et al. Inhibition of several strains of influenza virus in vitro and reduction of symptoms by an elderberry extract (Sambucus nigra L.) during an outbreak of influenza B Panama. J Altern Complement Med 1995;1:361-369.

3 Zakay-Rones Z, et al. Randomized study of the efficacy and safety of oral elderberry extract in the treatment of influenza A and B virus infections. J Int Med Res 2004;32:132-140.

4 De Flora S, et al. Attenuation of influenza-like symptomatology and improvement of cell-mediated immunity with long-term N-acetylcysteine treatment. Eur Respir J 1997;10:1535-1541.

5 Cathcart RF. Vitamin C: the nontoxic, nonrate-limited, antioxidant free radical scavenger. Med Hypotheses 1985;18:61-77.

6 Cathcart RF III. Vitamin C, titrating to bowel tolerance, anascorbemia, and acute induced scurvy. Med Hypotheses 1981;7:1359-1376.

7 Yamada H, et al. Gargling with tea catechin extracts for the prevention of influenza infection in elderly nursing home residents: a prospective clinical study. J Altern Complement Med 2006;12:669-672.

8 Matsumoto K, et al. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial. BMC Complement Altern Med 2011;11:15.

9 Cannell JJ, et al. Epidemic influenza and vitamin D. Epidemiol Infect 2006;134:1129-1140.

10 Urashima M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr 2010;91:1255-1260.

11 Jorde R, et al. Vitamin D supplementation did not prevent influenza-like illness as diagnosed retrospectively by questionnaires in subjects participating in randomized clinical trials. Scand J Infect Dis 2012;44:126-132.