Hypercholesterolemia in diabetics with clinically unrecognised primary thyroid failure.

Forty-nine diabetics with primary thyroid failure, as indicated by an elevated TSH concentration (TSH 38.0 +/- 5.4 mU/L, T4 63.0 +/- 4.0 nmol/L), without overt clinical evidence of hypothyroidism, had a higher (p less than 0.025) mean plasma cholesterol concentration (6.8 +/- 0.2 nmol/L vs 6.0 +/- 0.2 nmol/L) than 49 euthyroid diabetics (TSH 3.16 +/- 0.2 mU/L, T4 99.1 +/- 2.81 nmol/L) of equivalent age, sex, weight, diabetic treatment and duration of diabetes. No significant difference in triglyceride concentration was observed between the two groups of diabetics. Thyroxine replacement therapy in 18 diabetics with subnormal T4 concentrations was associated with a reduction (p less 0.01) in mean plasma cholesterol concentration to 5.8 +/- 0.3 nmol/L, but no significant change in triglyceride concentration. Clinically unrecognised thyroid failure may contribute to the high mortality from ischaemic heart disease observed in diabetics by virtue of accompanying, reversible hypercholesterolemia.