What it is
Astragalus, a member of the pea family, has been used for more than 2,000 years in Traditional Chinese Medicine (TCM) as a popular tonic for strengthening qi (vitality) and resistance to disease. Today, researchers in the East and West are investigating astragalus for enhancing immune function, for treating viral diseases ranging from the common cold to hepatitis, and as a supportive therapy to bolster immune function in people undergoing cancer treatment.

Astragalus ups production of compounds such as immunoglobulin, which helps the immune system to resist infections and cancer.

How it works
No single compound in astragalus has been identified as the one that helps immune function. To date, most of the research has focused on the role of polysaccharides—large, complex sugar molecules that are found in a variety of plants and boost immunity.

Polysaccharides trigger the bone marrow and lymphatic tissue to create immune cells. They also prompt increased activity in these cells, which include T-cells, natural killer cells, and macrophages (large white blood cells that consume viruses and potentially cancerous cells). In addition, astragalus ups production of compounds such as immunoglobulin, which helps the immune system resist infections and cancer. Finally, polysaccharides (along with natural detergents called saponins and antioxidant flavonoids) may shield cells against damage from toxins, radiation, and other free radicals thought to contribute to cancer and other degenerative diseases.

3 more immune enhancers>>

1: Echinacea (Echinacea spp)
Boosts immune activity and fights infection; best taken at the first sign of a cold or flu.

2: Maitake (Grifola frondosa)
This medicinal mushroom contains polysaccharides that strengthen immunity; best taken regularly.

3: Shiitake (Lentinus edodes)
This medicinal mushroom has additional polysaccharides; best taken regularly.

To date, researchers have conducted most studies in the laboratory or on animals. Nonetheless, the results are promising. For example, in a 1997 Japanese study, researchers found that giving astragalus to elderly mice restored immune function to more robust levels, comparable to those found in 10-week-old mice (Biological and Pharmaceutical Bulletin, 1997, vol. 20, no. 11). In a 1995 Chinese clinical trial (yet to be published in English), researchers gave up to 30 grams of a concentrated astragalus extract daily to 115 people suffering from leucopenia (chronic low white blood cell count). After eight weeks of treatment, white blood cell counts increased significantly. TCM practitioners often give astragalus to reduce the negative side effects of cancer treatments, including reduced immune function. They usually prescribe astragalus in combination with other Chinese herbs and interferon, a drug that mimics proteins made by the immune system to fight viruses, bacteria, and cancer cells. In China, researchers are studying other uses of astragalus, including treatment of a variety of viral infections, such as HIV. Although results look promising, more ambitious clinical studies on humans are needed.

Side effects
Astragalus has no known side effects. In TCM, astragalus is never taken during the acute stage of an illness with fever, such as a cold or flu, because it is thought to exacerbate symptoms. Some American herbalists, however, cite a lack of research supporting this proscription.

How to take it
You can buy astragalus in many forms, including dried slices or shredded root, capsules, and liquid extracts. TCM practitioners often make astragalus tea or simmer root slices in soup. Preparations vary in potency; follow directions for best results.

Dried astragalus root costs approximately $2 per ounce; commercial preparations start at $8 for 100 capsules and $15 for 2 ounces of liquid extract.

Herbalist and author Laurel Vukovic lives in Ashland, Oregon and has published nine books, including Herbal Healing Secrets for Women (Prentice Hall, 2000).