Healthy effects exerted by prebiotics, probiotics, and symbiotics with special reference to their impact on the immune system.

Pre-, pro-, and symbiotics are endowed with a broad spectrum of beneficial effects when administered to animals and humans. A series of experimental and clinical studies have clearly demonstrated that prebiotics, probiotics, or their combination are very effective in attenuating chronic inflammatory conditions such as inflammatory bowel disease or obesity. In addition, these natural products are able to prevent or arrest tumor development, acting on the intestinal microbiota as well as potentiating the immune response. Aging is characterized by a dramatic reduction of both innate and adaptive immune responses, the so-called immunosenescence. This leads to an increased incidence of infections, autoimmune diseases, and cancer in the elderly. Pre-, pro-, and symbiotic administration has been shown to ameliorate the immune response in aging. In particular, administration of a symbiotic to free-living elderly was able to potentiate the release of interleukin-8, thus increasing neutrophils in the host, perhaps explaining the reduced frequency of winter infections in the elderly