['Statins are effective in the primary and secondary prevention of cardiovascular events in individuals with and without diabetes. Emerging evidence, however, suggests that statins might reduce insulin sensitivity and secretion in healthy population and in type 2 diabetes.', 'We aimed to investigate the effect of statin therapy introduction on insulin sensitivity in patients with type 1 diabetes mellitus (T1DM).', 'This prospective observational 56-month long study included 832 randomly selected T1DM patients aged 25 to 61\xa0years. Uncontrolled dyslipidemia and clinician-perceived need for treatment, rather than randomization, were basis for individuals being started on either atorvastatin or simvastatin (10-40\xa0mg); N\xa0=\xa0345, 41.47%. Patients on statin treatment were compared with those unexposed to statin. Insulin sensitivity was assessed using equation derived from euglycemic-hyperinsulinemic clamp studies-estimated glucose disposal rate.', 'Patients who started statin therapy (N\xa0=\xa0345, 59.42% atorvastatin and 40.58% simvastatin) experienced a greater decrease in insulin sensitivity (19.27% vs 12.82% P\xa0<\xa0.001) and metabolic control deterioration compared with statin-free group. The risk of decrease in insulin sensitivity attributable to statin use was 36.7% (hazard ratio 1.36; 95% confidence interval 1.31-1.43) after adjustment for age, gender, disease duration, smoking status, and the concomitant antihypertensive therapy.'] Is statin treatment associated with insulin sensitivity decrease in type 1 diabetes mellitus : A prospective , observational 56-month follow-up study?