Probiotics are living microorganisms that confer health benefits when they are consumed in sufficient doses. Many of these microbes are natural inhabitants of your gastrointestinal tract. Your intestine normally harbors several hundred different species of "friendly" bacteria that help to promote healthy digestion and prevent the growth of harmful organisms. Probiotics contribute to your health in other ways, too.
The Hygiene Hypothesis
Although its origins are uncertain, the hygiene hypothesis proposes that infants who are not exposed to a sufficient number of microbes -- including probiotic organisms -- are more likely to develop immunologic conditions, such as hay fever and autoimmune diseases, later in life. More than 20 years ago, Dr. David Strachan noted that children in larger families who were exposed to more microorganisms developed fewer allergic diseases than children from small families. Strachan first published his observations in the "British Medical Journal" in 1989. When the populations of East and West Germany were reunited by the destruction of the Berlin Wall in 1999, Dr. Erika von Mutius discovered that children from the East, who had lived in poorer, dirtier conditions for many years, had fewer problems with allergies and asthma than their Western counterparts. Von Mutius summarized her impressions in the "Journal of Allergy and Clinical Immunology" in 2002.
Probiotic Benefits
In addition to maintaining a natural microbial diversity within your gut, supplemental probiotics have been shown to confer a variety of other health benefits. In a 2008 article published in "Advances in Biochemical Engineering/Biotechnology," Dr. Michael de Vrese reviewed some of these benefits, which include amelioration of viral or bacterial diarrhea, reduction of cancer-promoting enzymes and metabolites in the gut, a decrease in irritable bowel symptoms, improvement in inflammatory disorders of the intestine, alleviation of constipation, reduction of allergic disorders in infants, prevention of symptoms of lactose intolerance, treatment of urinary tract infections and prevention of respiratory infections, such as colds and flu.
Why Probiotics Work
The reasons behind probiotics' protective effects are not completely understood, but it is presumed that they exert their influence on human health by modulating the immune response. According to a 2008 article published in "Advances in Experimental Medicine and Biology," specific strains of probiotics have demonstrated the ability to stimulate and regulate both innate and acquired immune responses. This includes the induction or suppression of immune messenger molecules, the recruitment of immune cells and the modulation of antibody production. Immune cells in the lining of your respiratory and gastrointestinal tracts help to protect you from a wide array of viruses and bacteria. Because probiotics are foreign entities, they activate these cells -- macrophages, natural killer cells and lymphocytes -- to a level of function that enhances their infection-fighting capabilities. However, probiotics are not pathogenic, so they don't actually invade healthy tissues.
Probiotics for Colds and Flu
According to a 2009 review in the "International Journal of Antimicrobial Agents," probiotics have a demonstrated ability to reduce the duration and severity of respiratory infections, including colds and flu. However, the probiotic strains included in this review -- Lactobacillus, Bifidobacterium and Entercoccus faecalis -- did not reduce the incidence of such infections. In contrast, other studies have shown a decrease in the risk of upper respiratory infections when specific probiotic strains were used. For example, Lactobacillus GG demonstrated the ability to reduce both the risk and duration of colds in daycare children in a 2010 "Clinical Nutrition" study.
Recommendations
The optimal dosage and composition of probiotic supplements have not been clearly defined. Some probiotic strains have exhibited greater efficacy for specific conditions or they have simply been more extensively studied. Currently, preparations that include multiple strains and contain several hundred million to several billion viable organisms are the most popular. Pregnant women and individuals with underlying medical conditions are advised to consult their physicians before taking probiotics.
References
- "British Medical Journal"; Hay Fever, Hygiene, and Household Size; Strachan D; 1989
- "The Journal of Allergy and Clinical Immunology"; Environmental Factors Influencing the Development and Progression of Pediatric Asthma; 2002
- "Advances in Biochemical Engineering/Biotechnology"; Probiotics, Prebiotics, and Synbiotics. De Vrese M, Schrezenmeir J; 2008
- "Advances in Experimental Medicine and Biology"; Probiotics, Immunomodulation and Health Benefits; Gill H, Prasad J; 2008
- "International Journal of Antimicrobial Agents"; Probiotics for the Prevention of Respiratory Tract Infections: A Systematic Review; Vouloumanou E, et al.; 2009
- "Clinical Nutrition"; Lactobacillus GG in the Prevention of Gastrointestinal and Respiratory Tract Infections in Children Who Attend Day Care Centers: A Randomized, Double-Blind, Placebo-Controlled Trial
