Ginseng, the root of the plant Panax ginseng, is one of the most commonly used herbal medicines and is often sold as an over-the-counter remedy for fatigue. Although it has been used by humans for thousands of years, more recent research has begun to investigate therapeutic and pharmacological uses including anti-allergy and anti-inflammatory properties. It is also known to act on the immune system and to affect viral replication. And it may also be a very effective way of preventing the flu.
The findings of a recent study we carried out suggest that normal consumption of Korean red ginseng extract by healthy individuals could prevent infections by different flu virus strains. And studies in mice suggest that long-term ginseng intake could confer and prepare immune systems with better resistance to fight future pathogens.
The effect that ginseng has on flu virus infections regardless of strain makes it different from the strain-specific protection from annual vaccinations (often given to those most at risk such as the elderly and pregnant women, and determined by the strains in most circulation in a given year) and prescribed antiviral drugs such as Tamiflu – which recently came under fire over its effectiveness as a treatment against severe flu.
Korean red ginseng extracts are produced by steaming and drying the fresh roots of six-year-old Panax ginseng plants. These are then boiled in water and the supernatants – or liquids above the settled material – are concentrated. It is this preparation that can be designated as “red ginseng extract.” Because of its prominent biological effects, extracts from this particular plant have been used in animal studies. Despite known beneficial effects on human health and its action on viral infection, the mechanism for how it does this remains largely unknown.
In previous studies, we investigated the effects of ginseng given orally in mice – the most common way that healthy people take ginseng as a supplement. We found that this gave the mice a moderate but significant resistance to infection with the 2009 pandemic flu virus strain – on the whole it didn’t prevent illness, which was shown by them losing weight, but it did result in better survival.
Protection from ginseng given before infection wasn’t strong because the mice still became ill but we also found that treating them with ginseng after infection gave even less protection.
However most human adults who consume ginseng already have some immunity to the flu, either through previous contact with the virus or vaccination. So we tried giving ginseng instead to vaccinated mice instead through oral doses and found that it significantly improved how well the mice were able to fight different strains of flu viruses through cross-protection.
Infection of mice with a mixture of influenza virus and ginseng extract resulted in better clearance of lung viral levels and lower levels of inflammatory cytokines, the small proteins that are important in helping cells to send signals. But it also led to higher levels of antiviral cytokines. From these lab tests we know that Korean red ginseng extract may inhibit the flu virus growing. The extract appears to have multiple mechanisms against fighting infectious diseases, which might be beneficial if taken in healthy mice with previous exposure and prior to infections.
Our more recent study, published in Nutrients found that ginseng improved the survival of human lung epithelial cells (tissue cells that line cavities in the lung) when someone is infected with the flu virus. Also, ginseng treatment reduced the expression of pro-inflammatory genes, probably in part by interfering with chemically reactive molecules that contain oxygen and which are formed by the flu virus.
Taking ginseng for a longer term (around 60 days) showed multiple effects on the immune system of mice such as stimulating anti-viral protein production after flu virus infection. Ginseng also inhibited the infiltration of inflammatory cells into the lungs in mice. So ginseng might have potential beneficial effects in preventing flu virus infections by acting on the immune system in multiple ways.
Small doses of ginseng have been taken in humans for many years with no major side effects. But while ginseng looks like a promising way to help prevent flu, results only relate to healthy individuals taking normal doses. Based on animal studies it also has shown no or only minimal protective beneficial effects if treated after the onset of symptoms.
Sang-Moo Kang has received funding from NIH/NIAID grants and the Korean Ginseng Corporation for his research
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