Effects of Photobiomodulation on Metabolic, Inflammatory, and Neurological Outcomes in Type 2 Diabetes: A Systematic Review and Meta-Analysis

Type 2 diabetes mellitus (T2DM) is a global health burden characterized by hyperglycemia, oxidative stress, and systemic inflammation, which leads to complications that remain insufficiently managed by standard therapies. Photobiomodulation therapy (PBMT) has been proposed to be a complementary approach, but its effects in T2DM are unclear. We conducted a systematic review and meta-analysis of randomized controlled trials to evaluate the effects of PBMT on metabolic, inflammatory, and neurological outcomes in adults with T2DM. Five databases were searched until June 2025 (PROSPERO CRD420251083550) for relevant studies. Metabolic, inflammatory, and neurological outcomes were defined a priori as primary outcomes and were synthesized narratively due to substantial heterogeneity and incomplete reporting that precluded valid quantitative pooling. Although periodontal outcomes were not predefined as primary outcomes, they were reported in multiple trials; thus, these were analyzed quantitatively as secondary outcomes where sufficient homogeneity enabled meta-analysis. The narrative synthesis of primary outcomes showed inconsistent and largely short-term effects on glycemic control, systemic inflammation, and neurological function. In contrast, meta-analysis of secondary periodontal outcomes demonstrated modest but statistically significant improvements in clinical attachment level (-0.21 mm) and probing depth (-0.25 mm), with no effect on plaque index. Overall, the certainty of the evidence was low. PBMT may offer statistically significant but small adjunctive periodontal effects in adults with T2DM. However, the certainty of evidence is low, and these effects are unlikely to be clinically meaningful in isolation. Evidence for systemic metabolic, inflammatory, and neurological outcomes is preliminary and requires confirmation in larger, standardized RCTs.