Probiotics are defined as living microorganisms which when administered in adequate amounts confer a health benefit to those taking them. Health benefits can be attributed to an ability to assist the natural microflora, either to re-establish itself following imbalance or to upregulate (meaning an increase in cellular response to a molecular stimulus due to increase in the number of receptors on the cell surface) vital metabolic functions of the bacteria.
Only a few select cultures have actually been proven to be beneficial and justifiably be called ‘Probiotics’ and include certain strains of Lactic Acid Bacteria (including Lactobacilli and Bifidobacteria) which have conclusive health benefits when taken.
Gut microbiota play an important role in:
-Maintenance of appropriate gut pH
-Digestive function through enzyme activity
-Modulation of immune function
-Production of antimicrobial substances, thus defending against invaders and maintaining a balance of microflora
-Synthesis of certain vitamins
-Production of amino acids and recylcing of nitrogen
-Synthesis of short chain fatty acids
-Detoxification and transformation of many substances
There is also growing evidence that probiotic supplements may be helpful in some specific conditions, notably side effects of antibiotics, irritable bowel syndrome, general immune support, allergy and upper respiratory tract infection.
Given these potential benefits, there is interest in the use of probiotics specifically in athletes to help maintain overall general health, enhance immune function or reduce URTI incidence and symptom severity/duration.
To date, most studies of probiotic interventions in athletes have been relatively small scale, but there is growing evidence pointing to a benefit in a number of areas which will be of interest to athletes in terms of their ability to maintain and/or boosting immune function through well understood mechanisms of action.
Source: http://www.ncbi.nlm.nih.gov/pubmed/24159152