Objective: Insulin need for a given degree of glucose control varies markedly among individuals. We examined which factors determine daily insulin use in patients with Type 1 diabetes.
Methods: A cross-sectional study was performed in 416 patients. Clinical parameters, medication use, physical activity, smoking, alcohol consumption, and laboratory parameters were determined.
Results: Body mass index and waist circumference were positively related to daily insulin use (2.3 U/kg/m(2), 95% CI=1.9-2.7 and 0.8 U/cm, 95% CI=0.6-0.9, adjusted for age and sex). Age, female sex, and duration of diabetes were inversely related to daily insulin dose. There was an increase of 3.6 U of insulin per mmol/l triglycerides (95% CI=1.04-6.2) and a decrease of 5.9 U of insulin per mmol/l high-density lipoprotein cholesterol (95% CI=-10.0 to -1.8), adjusted for age, sex, and weight. For blood pressure-lowering drugs, the strongest relation was found for thiazide diuretics (difference of 7.1 U insulin/day, 95% CI=0.2-14.2, adjusted for age, sex, and weight). The use of an insulin pump and physical activity were related to lower daily insulin need: -8.7 U/day (95% CI=-11.8 to -5.5) and -1.7 U/day per activity score unit (95% CI=-3.2 to -0.2), respectively, adjusted for age, sex, and weight. Smoking was related to an increased need of 5.3 U/day (95% CI=1.5-9.0), adjusted for age, sex, and weight.
Conclusions: Our results show that components of the metabolic syndrome are positively related to daily insulin use. Also, decreased physical activity, smoking, and the use of blood pressure-lowering drugs, which influence insulin sensitivity, are associated with an increased insulin need. These findings suggest that the presence of insulin resistance in Type 1 diabetes or "double diabetes" plays a key role in determining daily insulin need.