Current applications of probiotics focus on prevention and/or treatment of gastrointestinal diseases and immune mediated diseases. In all clinical trials with probiotics which have been conducted to date (and listed at https://clinicaltrials.gov/ ), a total of 713 different diseases and conditions have been studied. The top 10 of conditions investigated most is dominated by gastrointestinal diseases and digestive system diseases. From these clinical studies—most of them performed on patients—the beneficial effects of probiotics for a number of gastrointestinal diseases, including diarrhoea, have been demonstrated. It is unfortunate that due to regulatory frameworks, this evidence cannot be used to substantiate health claims for probiotics in this domain. To a certain degree this also holds true for immune mediated disease.
Clinicaltrials.gov lists 86 studies on probiotics that are not recruiting yet, or are active but not recruiting yet. These include clinical trials on communicable disease, endocrine diseases, mental disorders and psychotic disorders. With an aging population, and with a growing body of evidence for the importance of the gut-brain axis, it could be expected that there also would be increased attention for the application of probiotics in neurodegenerative diseases. The number of clinical studies on potential beneficial effects of probiotics in diseases such as Parkinson and Alzheimer however is disappointingly low, with just 5 studies registered at clinicaltrials.gov. That amounts to 0.1 percent of all clinical studies for this domain. It should be added that 2 of those studies address the problem of constipation in Parkinson’s, and not the primary disease process.
The phrase ‘Que sera sera, whatever will be will be’ has a flavor of theological predestination. While it is impossible to predict the future, the future can be shaped. Investing time and effort in setting up appropriately designed and powered clinical studies with relevant endpoints can form the basis for future therapies of neurodegenerative diseases. While reversion of the disease process may be impossible, halting or slowing down progression of the disease would already be a major step forward.
The song Que sera sera was first used in the Hitchcock movie called The Man that Knew Too Much. For future applications of probiotics, we still know too little, so let the investigations begin.