Individuals with Sjögren’s syndrome appear to have imbalances in their oral and gut microbiota that can cause poor digestion and worsen symptoms such as reduced salivary flow leading to dry mouth. Yet, studies to date have produced variable results, meaning that some studies have found differences between individuals living with Sjögren’s and healthy controls, while others have not. A systematic review set out to synthesize existing data and support a more well-informed understanding about the link between Sjögren’s and gut health.
The review study, “Healthy Patients Are Not the Best Controls for Microbiome-Based Clinical Studies: Example of Sjögren’s Syndrome in a Systematic Review,” was published in the journal Frontiers in Immunology.
More and more research now supports the role of gut microbiota in both the immune system and brain health. Like any healthy ecosystem, the human microbiota consists of vast colonies of bacteria that live and work in harmony. That said, the health of the ecosystem depends on various factors such as one’s age, diet, exposure to microorganisms, antibiotic therapy and so forth. An imbalance in bacteria is known as dysbiosis and has been shown to trigger or worsen several health conditions, including inflammatory arthritic conditions such as Sjögren’s. However, it is unclear if microbiota imbalance is a consequence of or part of the underlying causes of Sjögren’s.
A team of researchers in France systematically reviewed published studies, from January 2000 through June 2020, that compared the oral and gut microbiota of Sjögren’s patients to a control group. These studies were primarily cohort studies, meaning that individuals with and without Sjögren’s were followed for a period of time. A total of 289 articles were retrieved from database searches, 45 studies were read in full, and 18 of them were included in the analysis. A total of 13 studies reported data on oral microbiota, four on gut microbiota, and one on both oral and gut microbiota.
Combined, the 18 included studies had a sample of 330 Sjögren’s patients with information about their oral microbiota and 120 with data on their gut/fecal microbiota. On the other hand, the control group included healthy volunteers as well as people with sicca symptoms (dry mouth), but without a Sjögren’s diagnosis. The results were rather contradictory. Several studies reporting lower bacterial diversity in both oral and gut microbiota among Sjögren’s patients, while others found no differences between Sjögren’s patients and the control group.
Possible explanations include the fact that the researcher did not account for lifestyle factors such as smoking status, medication intake, and dental hygiene. Further, the sampling methods for microbiota varied. For instance, an oral sample could have been collected through either buccal swab, oral washing, or from either unstimulated or stimulated saliva. Additionally, methods of data analysis differed among the studies, and each includes their own strengths and limitation.
Despite the challenges mentioned above, researchers noted reduced salivary secretion explained more microbial changes, suggesting that dysbiosis is a consequence of and not the underlying cause of Sjögren’s. Further, the authors noted a strength of their review which is the inclusion of sicca patients who may be a more appropriate control group to assess the effect of Sjögren’s itself on microbiota, as it eliminates the effects of lower production and flow of saliva. The team also emphasized the importance of standardized methods for assessment to allow clearer conclusions to be drawn in future.
Compiled by Ellen Wang