Voluntary Exercise Delays Type 1 Diabetes Onset Independent of Splenic T Cell Subsets and Inflammatory Cytokines in NOD Mice

Objectives: This study aimed to assess the effects of voluntary exercise on type 1 diabetes mellitus (T1D) development and splenic immunological profiles in non-obese diabetic (NOD) mice, a spontaneous model of human T1D. Methods: Prediabetic female NOD mice were randomly assigned to sedentary or exercise groups, with mice in the exercise group given 10-week wheel access and sedentary mice receiving none. Late-time mice were monitored to diabetes onset or 24 weeks of age; early-time mice were analyzed immediately post-intervention. Blood glucose, food intake, water consumption, and body mass were monitored weekly. At the endpoints, splenocyte counts, T and B cell subsets, and mitogen-stimulated cytokine production were analyzed using flow cytometry. Results: Mice in the exercise group ran an average of 20.76 ± 0.22 km/day. By the late-time endpoint, 75% of mice in the exercise group remained non-diabetic versus 35% of sedentary mice (p = 0.006). Mice in the exercise group demonstrated lower blood glucose (p = 0.015), visceral fat mass (p = 0.035), and water intake (p < 0.001) but higher food intake (p = 0.001), with no difference in body mass (p = 0.389) compared to sedentary mice. No differences were observed in splenocyte counts or Th, Tc, Treg, or B cell populations at either time point (p ≥ 0.185). Early-time point cytokines also did not differ between groups (p ≥ 0.08). Conclusions: Voluntary exercise reduces T1D incidence and mitigates hyperglycemia in NOD mice, suggesting a protective effect against disease progression. Despite the benefits, physical activity did not alter splenic Tcell subsets or inflammatory cytokines, demonstrating systemic immunomodulation may not be the primary driver of benefit. Our results indicate that voluntary exercise protects against T1D through tissue-specific or metabolic mechanisms, which warrant further mechanistic investigation.