Purpose <p>multiple sclerosis is a chronic autoimmune disease that affects the central nervous system. It damages the myelin sheath that covers nerve fibers, resulting in neurological symptoms, including muscle weakness, vision problems, and difficulty with coordination and balance. Probiotic bacteria have been shown to have a potential role in managing multiple sclerosis by modulating the immune system and reducing inflammation. They modulate the immune system by increasing the production of anti-inflammatory cytokines, including IL-10, TGF-β, and IL-4, and reducing the levels of pro-inflammatory cytokines, such as IFN-γ and IL-17. Probiotics may also improve gut barrier function, which can help prevent the entry of harmful substances into the bloodstream that could trigger an immune response.</p> Methods <p>The presented double-blind, placebo-control clinical trial was conducted to investigate the effect of a novel supplement containing probiotics and vitamin D, so IL-10, TGF-b, IL-4, IL-17, and IFN-gamma cytokines, and neurofilament light chain biomarker were measured by ELISA. Also, we determined the EDSS score and quality of life for patients.</p> Results <p>the results revealed that consuming the supplement for twelve weeks can significantly reduce the concentration of NFL biomarker compared to the control group. For the first time, these valuable results demonstrate the effect of probiotic bacteria on reducing this biomarker. Also, the results showed a significant decrease in IL-17 and IFN-γ and modulatory effects on IL-4 and TGF-β. On the other hand, a considerable rise is demonstrated in the IL-10 level.</p> Conclusion <p>These findings could provide the supplement as a novel co-therapeutic strategy for multiple sclerosis.</p>