Feasibility of Multi-Wavelength LED Irradiation on the Skull and Preliminary Glycemic Outcomes in Individuals with Type 2 Diabetes: A Prospective Pilot Study

Background: Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by impaired glucose homeostasis, insulin resistance, and progressive β-cell dysfunction. Increasing evidence suggests that glucose homeostasis is regulated not only by peripheral metabolic organs but also by central nervous system and autonomic pathways. Photobiomodulation (PBM) has been reported to modulate mitochondrial function, oxidative stress, vascular responses, and neural activity; however, its potential influence on glycemic outcomes remains largely unexplored. Objective: This prospective pilot study aimed to evaluate the feasibility of applying multi-wavelength LED irradiation to a predefined cranial region and to explore preliminary glycemic outcomes in individuals with T2DM. Methods: Seven participants with physician-diagnosed T2DM receiving stable antidiabetic medication regimens were enrolled. Multi-wavelength LED irradiation (660, 850, and 940 nm) was applied bilaterally to the predefined S3 region of the skull. Irradiation parameters included an irradiance of 5 mW/cm2 (0.005 W/cm2), an energy density of 4.5 J/cm2, and an exposure duration of 900 s per session. Treatments were administered three times weekly for four weeks (12 sessions). Primary outcome measures included fasting blood glucose (Glucose AC) and glycated hemoglobin (HbA1c). Secondary outcomes included mean blood glucose, fasting insulin, C-peptide, homeostasis model assessment of insulin resistance (HOMA-IR), lipid profile, and C-reactive protein (CRP). Exploratory paired statistical analyses were performed following assessment of data normality using the Shapiro–Wilk test. Results: Following the four-week intervention, fasting blood glucose and mean blood glucose were significantly reduced (p = 0.026 and p = 0.044, respectively), whereas HbA1c demonstrated a borderline reduction (p = 0.051). Changes in fasting insulin, C-peptide, HOMA-IR, lipid profile, and CRP were variable and did not reach statistical significance. No intervention-related adverse events were observed, and all participants completed the study protocol. Conclusions: Multi-wavelength LED irradiation applied to the predefined S3 region of the skull was feasible, safe, and well tolerated in individuals with T2DM. The observed preliminary glycemic outcomes support the feasibility of further investigation in larger randomized controlled trials. However, because of the small sample size, absence of a control group, and exploratory study design, the present findings should be interpreted cautiously and should not be considered evidence of clinical efficacy or causal effects.