Natural killer cells are a type of white blood cell that can kill cancer cells or virus-infected cells by triggering a number of cell-destroying pathways. Some foods may confer immune-enhancing benefits by increasing numbers and activity of natural killer cells. Check with your doctor, however, before using foods to prevent or treat a medical condition.
Maitake and other medicinal mushrooms enhance the activity of natural killer cells, according to Peter C.K. Cheung, author of the book "Mushrooms as Functional Foods." A study published in the February 2010 issue of the "Journal of Medicinal Food" found that maitake mushrooms increased natural killer cell activity and inhibited colon cancer in laboratory animals.
Probiotics, the good bacteria found in yogurt and other fermented foods, stimulate production of a component of the immune system which, in turn, stimulates natural killer cell activity, according to Edward R. Farnworth, editor of the "Handbook of Fermented Functional Foods." People with low levels of natural killer cells experience greater benefits of probiotic supplementation than people who already have high levels of natural killer cells. In a study of colorectal cancer patients published in the November 2010 issue of the journal "Hepatogastroenterology," those who consumed probiotics showed significantly higher natural killer cell activity, implying that these patients had lower-than-average levels of natural killer cells at the start of the study.
Panax ginseng contains a polysaccharide called ginsan that stimulates natural killer cell activity, according to a study published in the August 2011 issue of the journal "Immunology Letters." Part of the effect of increased natural killer cell activity is to control your immune response to prevent excessive immune activity. When natural killer cell levels are low, the immune system can malfunction and attack body cells, leading to an autoimmune condition. Panax ginseng exhibits this type of immune regulation and may be beneficial as a therapy for multiple sclerosis and other autoimmune conditions.
Compounds in soybeans, known as saponins, inhibit herpes and other viruses by increasing natural killer activity, according to KeShun Liu, editor of the book "Soybeans as Functional Foods and Ingredients." Researchers at the Division of Immunoregulation, Institute for Genetic Medicine, at Hokkaido University in Japan found that a variety of Japanese soybean activated natural killer cell activity, suggesting that soybean may be a useful immune-enhancing food.