Probiotics in the form of yoghurt, cheese and sauerkraut have been consumed for years without any ill effects. Due to this spotless record, probiotic supplements, which have only been popular in the last twenty years, were assumed to be safe. However, high doses of single strains of bacteria present new challenges and risks. What do you need to know about probiotics safety?
In actuality, Lactobacilli and Bifidobacteria can be the culprits during infectious endocarditis (inflammation of the inner layer of the heart) and bacteremia (the presence of bacteria in the blood). Approximately 0.05%–0.4% of patients with these diseases have infections of common milk bacteria. Reports of fungemia (infection with fungal species) are also reported for Saccharomyces cerevisiae, which is a common yeast that has some beneficial uses.
However, it is important to note that these same patients often have a severe underlying condition that makes them susceptible to infection by normally friendly bacteria. As it was mentioned in the article about probiotics, even the friendliest bacteria can become a foe if it is allowed to colonize certain areas of the body. Studies using probiotics in patients with severe pancreatitis particularly brought this point home.
A Dutch clinical trial wanted to see if probiotics could function more effectively than antibiotics in controlling bacteremia and pneumonia in acute pancreatitis patients. Pancreatitis is increasing in prevalence in Europe and is associated with fatal bacterial infections that cannot be controlled by antibiotics alone. As probiotics have a good reputation for controlling the overgrowth of “bad” bacteria, it seemed logical to try to help these patients with probiotics. However, probiotics proved to be deadly in these patients. More patients died within the probiotics treated group than in the placebo treated group (16% versus 6%) and some probiotic treated patients developed bowel ischaemia.
Bowel ischaemia is a form of colitis that develops as a result of loss of blood flow to the colon. Without enough blood, cells become starved for oxygen and nutrients. It was not clear why this particular complication developed as it was never before associated with probiotic use. The researchers speculated that the probiotic administration might have increased the demand for oxygen and nutrients so much so that the cells of the colon were eventually deprived of what they needed.
This incident is a reminder that probiotics can be dangerous in patients with extremely severe diseases. Yet, the trick is to define which situations are dangerous. Critically ill patients undergoing surgeries such as transplantation or liver surgery given beneficial bacteria actually benefitted from them. And a Finland study showed that the recent introduction of probiotic-enriched yoghurts has not increased the incidence of infections in the general population.
Because of the growing concern about the use of probiotics in clinical trials, the Agency for Healthcare Research and Quality, part of the U.S. Department of Health and Human Services, performed a study looking at reported adverse effects in clinical studies performed before 2010. They found that most studies poorly reported adverse effects, which prevented a thorough analysis. However, they cautiously stated that there appeared no increased risk in both patient and healthy control groups receiving probiotics in the trials that they examined.
Researchers and clinicians are not ignoring the issues. There are calls to introduce standardized procedures for the use of probiotics in clinical trials to better characterize side effects and efforts to fully assess the safety of all probiotics on the market. There is also now the awareness that the patient’s health status has a lot to do with probiotic safety. Although probiotic safety is now in the spotlight, real guidelines will probably not be available anytime soon. Consumers need to take the time to assess the current information and consult their healthcare providers before ingesting potentially beneficial bacteria, especially if they have severe underlying
Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment.
- Besselink, M. G. H., van Santvoort, H. C., Buskens, E., Boermeester, M. A., van Goor, H., Timmerman, H. M., et al. (2008). Probiotic prophylaxis in predicted severe acute pancreatitis: a randomised, double-blind, placebo-controlled trial. Lancet, 371(9613), 651–659. doi:10.1016/S0140-6736(08)60207-X
- Borriello, S. P., Hammes, W. P., Holzapfel, W., Marteau, P., Schrezenmeir, J., Vaara, M., & Valtonen, V. (2003). Safety of probiotics that contain lactobacilli or bifidobacteria. Clinical Infectious Diseases, 36(6), 775–780. doi:10.1086/368080
- Hempel, S., Newberry, S., Ruelaz, A., Wang, Z., Miles, J. N., Suttorp, M. J., et al. (2011). Safety of probiotics to reduce risk and prevent or treat disease.
- Sanders, M. E., Akkermans, L. M. A., Haller, D., Hammerman, C., Heimbach, J., Hörmannsperger, G., et al. (2010). Safety assessment of probiotics for human use. Gut Microbes, 1(3), 164–185. doi:10.4161/gmic.1.3.12127