Efficacy of probiotics as an adjuvant therapy for periodontitis in patients with type 2 diabetes mellitus: an updated meta-analysis of randomized controlled trials

To assess the efficacy of probiotics as an adjunct to non-surgical periodontal therapy (NSPT) for periodontitis in patients with type 2 diabetes mellitus (T2DM). Seven electronic databases were searched from inception to February 1, 2026. Only randomized controlled trials comparing probiotics plus NSPT with NSPT alone or placebo plus NSPT were eligible. Study selection, data extraction, and risk-of-bias assessment were performed independently by two reviewers. Random-effects meta-analyses were conducted using mean differences or standardized mean differences with 95% confidence intervals. To avoid conflating short- and longer-term effects, outcomes were pooled separately according to follow-up time point. Eight RCTs reported in nine publications involving 511 participants were included in this meta-analysis, including 257 participants in the intervention groups and 254 participants in the control groups. Adjuvant probiotic therapy did not significantly improve probing depth at 30, 60, 90, or 180 days, or clinical attachment level at 90 or 180 days. Among secondary periodontal outcomes, gingival index showed statistically significant differences at 30 and 90 days in favour of the control group, but not at 60 days, whereas sulcus bleeding index favoured probiotics at 90 days. For systemic outcomes, high-sensitivity C-reactive protein was significantly reduced, whereas interleukin-6, tumour necrosis factor-alpha, and glycated haemoglobin did not differ significantly between groups. In patients with periodontitis and T2DM, current randomized evidence does not support consistent additional benefits of probiotics for the principal periodontal or metabolic endpoints. Improvements observed in selected bleeding- and inflammation-related outcomes may reflect a short-term anti-inflammatory effect, but the evidence remains too limited and heterogeneous to support routine clinical recommendation.