Scientists caution against long-term probiotic use, finding rare adverse health risks

20 May 2024 --- Japanese researchers linked the probiotic strain Clostridium butyricum with the prevalence of bacteremia — a condition where bacteria circulate in the bloodstream. The team from Osaka University cautions that while probiotics provide various health benefits, the study shows that even such agents can present with severe but rare adverse events.

The researchers studied the genetic materials of bacteria in hospitalized patients with bacteremia who were admitted to Osaka University Hospital between September 2011 and February 2023. Among the 6,576 patients with positive blood cultures for bacteria, the team found five (0.08%) cases of C. butyricum bacteremia. 

All five patients consumed C. butyricum probiotics, commonly prescribed in Asia. The researchers confirmed that all bacteremia strains were probiotic derivatives. 

Most patients had compromised immune systems, with common symptoms being fever and abdominal distress. One patient died within 90 days after the bacteremia diagnosis. 

“We hope that by raising awareness that probiotics are not harmless entities and can, albeit rarely, cause diseases such as bacteremia, unnecessary use of probiotics can be avoided,” Ryuichi Minoda Sada, MD, the study’s lead author, tells Nutrition Insight.

“This research can communicate that probiotics are not necessarily harmless for consumers and patients. Accurately assessing these results requires studies using multicenter prospective observational trials among probiotic users or research utilizing blood culture databases to determine the frequency of probiotic-related bacteremia.” 

Bacteremia health risk  
In two of the five cases of bacteremia, the researchers could not find a clear reason for the probiotic prescription. Four of the people with the condition were taking prescribed MIYA-BM probiotics at least a week before their hospitalization and stopped taking the product after their diagnosis. The results were published in Emerging Infectious Diseases. 

“This research can provide insights into which patients might be at risk for probiotic-related bacteremia,” comments Sada.

The researchers caution clinicians to avoid long-term, inappropriate prescription of probiotics for hospitalized patients.“Our findings indicate that all cases involved hospitalized patients, many of whom were immunocompromised, suggesting that such conditions may be risk factors.” 

In addition, the research team found a consistent pattern of antibiotic susceptibility in all clinical strains, consistent with previous reports on the strain. They note that C. butyricum is susceptible to antibiotics such as penicillin, ampicillin and cefmetazole. 

Probiotic use 
The researchers note that reports on probiotic-related bacteremia are scarce, adding that studies have yet to evaluate the genetic similarities among these reports. 

Sada adds that, at present, “it is not possible to answer the risk of developing bacteremia from other probiotics.” More research is needed to elucidate this. 

According to the authors, multicenter studies are needed to clarify the prevalence of C. butyricum bacteremia and the genetic origin of the strains. Moreover, the duration of probiotic use was based on information from medical records, while the precise durations were not always apparent. 

The study cautions: “Clinicians must avoid long-term, inappropriate prescription of probiotics for hospitalized patients with multiple comorbidities, including immunosuppressive treatment and intra-abdominal problems, to prevent bacteremia caused by probiotics.”

Meanwhile, the health benefits of probiotics are increasingly subscribed to by both research and the nutrition industry. Research links probiotics to blocking mercury absorption in the gut and reducing weight in obese dogs. 

A probiotic strain by Novonesis was recently approved for gut and brain health, while Kaneka Probiotics was authorized to sell a probiotic for gut and skin health. 

By Jolanda van Hal