To evaluate the association between statin therapy, cardiorespiratory fitness (CRF), body mass index (BMI), and progression to insulin therapy in type 2 diabetes mellitus (T2DM).

Participants were patients with T2DM (mean age, 62.7±8.4 years; men, 178,992; women, 8360) not treated with insulin, with no evidence of uncontrolled cardiovascular disease, who completed an exercise treadmill test between October 1, 1999, and September 3, 2020. Of these, 158,578 were treated with statins and 28,774 were not. We established 5 age-specific CRF categories according to peak metabolic equivalents of task achieved during an exercise treadmill test.

During a median follow-up period of 9.0 years, 51,182 patients progressed to insulin therapy with an average annual incidence rate of 28.4 events/1000 person-years. The adjusted progression rate was 27% higher in statin-treated patients (hazard ratio [HR], 1.27; 95% CI, 1.24 to 1.31), related directly to BMI and inversely related to CRF. A progressively higher rate was noted in statin-treated vs non-statin-treated patients within all BMI categories, ranging from 23% for normal weight to 90% for those with BMI of 35 kg/m and higher. The statin-CRF interaction revealed 43% higher rate in the least-fit statin-treated patients (HR, 1.43; 95% CI, 1.35 to 1.51) and a progressive decline with increased CRF to 30% lower risk in highly fit statin-treated patients (HR, 0.70; 95% CI, 0.66 to 0.75).

In patients with T2DM, the statin-related progression to insulin therapy was associated with relatively low CRF and high BMI levels. The progression rate was mitigated by increased CRF regardless of BMI. Clinicians should foster regular exercise for patients with T2DM to enhance CRF and to lessen the rate of progression to insulin therapy.