The effects of long-term administration of ginseng to humans have not been thoroughly evaluated. However, a new study gives us some clues on the effects of ginseng extracts on various immunoglobulins in mice. Ginseng extract (from powdered 4-year-old Korean white ginseng extracted by ethanol) was orally administered to healthy female mice for 52 days at doses of 30 and 150 mg/kg per day. Levels of serum protein and immunoglobulin isotypes were tested. Serum protein and albumin levels did not change, however, gammaglobulin levels did decrease in a dose-dependent manner. There are several isotypes of gammaglobulin, and the fraction that decreased was IgG1, without any significant decrease in the other Ig isotypes. The researchers state, "As IgG1 is rarely cytotoxic and can act as a blocking antibody, it is suggested that the selective decrease in serum IgG1 induced by ginseng extract without changes in the cytotoxic antibodies such as IgG2alpha may be helpful for the prevention and inhibition of cancer."
It's premature to make a prediction of a supplement preventing or inhibiting cancer based on a 52-day study on mice. There are so many complicating factors involved in cancer formation that even if a supplement helps in one particular area of the immune system, it may have detrimental effects on another aspect. However, ginseng has had much research devoted to it, and a long history of medicinal benefit. At this time, it seems that taking small amounts on a regular basis appears to be safe.
Kim YW, Song DK, Kim WH, et al. Long-term oral administration of ginseng extract decreases serum gamma-globulin and IgG1 isotype in mice. J Ethnopharmacology 58:55-58, 1997.