Insulin sensitivity modifies the relationship between thyroid function and lipid profile in euthyroid type 1 diabetic patients.

It has been suggested that association between hypothyroidism with dyslipidemia might be present already at the stage of normal thyroid function through altered insulin sensitivity. We analyzed the role of insulin sensitivity as a mediator of thyroid-induced lipid changes in euthyroid type 1 diabetic patients. Study included 304 patients with type 1 diabetes and normal thyroid function. Insulin sensitivity was measured with estimated glucose disposal rate calculated using the equation: eGDR = 24.31 - (12.22 × WHR) - (3.29 × HT) - (0.57 × HbA1c); WHR = waist-to-hip ratio, HT = hypertension. TSH, FT4, FT3, and serum lipids were measured. Correlations and multiple linear regressions analysis were performed to identify relationships between thyroid status and serum lipid parameters after stratifying patients in quartiles of eGDR. After adjustment for age, sex, BMI, duration of diabetes and insulin dose TSH, FT3, and FT4 was not significantly associated with serum lipids in all patients, independently of level of insulin sensitivity. However, after stratifying patients for the degree of insulin sensitivity in subjects in the lowest quartile of insulin sensitivity TSH was independently associated with LDL cholesterol (β = 0.210, p = 0.02). The independent relation of eGDR with TSH and LDL cholesterol suggests that the influence of thyroid function on lipid metabolism might extend into euthyroid range through altered insulin sensitivity.