Certain bacteria, specifically probiotic strains such as Lactobacillus and Bifidobacterium, have been investigated for their potential role in supporting or treating arthritis, particularly rheumatoid arthritis (RA). The rationale for their use stems from increasing evidence that the gut microbiome can influence systemic inflammation and immune modulation, both of which are relevant to autoimmune forms of arthritis. Several small-scale clinical trials and animal studies have suggested that supplementation with specific probiotic strains may help reduce inflammatory markers, improve gut barrier function, and alleviate some symptoms in people with RA. For example, a 2014 double-blind, placebo-controlled trial found that Lactobacillus casei supplementation for 8 weeks led to significant reductions in disease activity scores in RA patients compared to placebo. Other studies have shown improvements in inflammatory cytokine profiles and some symptom relief, although the magnitude of benefit tends to be modest.

However, while there is scientific interest and some promising preliminary data, the overall evidence base is still limited in size and quality. Most studies are small, short-term, and use varying strains and dosages, making comparisons difficult. Systematic reviews and meta-analyses conclude that probiotics may offer a mild adjunctive benefit, but they are not a replacement for standard medical therapies. The use of bacteria for osteoarthritis is much less studied and not well supported. Thus, while there is scientific validation for the use of certain bacteria in supporting arthritis management, the evidence is moderate and further research is needed to clarify efficacy and optimal protocols.