Insulin sensitivity regulates cholesterol metabolism to a greater extent than obesity: lessons from the METSIM Study

Abstract

Cholesterol synthesis is upregulated and absorption downregulated in insulin resistance and in type 2 diabetes. We investigated whether alterations in cholesterol metabolism are observed across the glucose tolerance status, from normoglycemia through impaired glucose tolerance to type 2 diabetes, in 781 randomly selected men 45 to 70 years of age from a population-based Metabolic Syndrome in Men Study. Cholesterol metabolism was assayed using surrogate serum markers, squalene, and noncholesterol sterols. The study population was classified into subgroups according to glucose tolerance as follows: normoglycemia, impaired fasting glucose, impaired glucose tolerance, and type 2 diabetes. LDL cholesterol did not differ between the groups. Cholesterol synthesis markers were lowest and absorption markers highest in normoglycemia. Sitosterol was lower in subjects with impaired fasting glucose compared with normoglycemic subjects (113 +/- 7 vs. 136 +/- 3 10(2) mumol/mmol of cholesterol, P < 0.05). LDL cholesterol was not associated with lathosterol/sitosterol ratio, a marker of cholesterol metabolism. Peripheral insulin sensitivity evaluated by the Matsuda index was associated with the lathosterol/sitosterol ratio in the entire population (r = -0.457, P < 0.001) and with that of lathosterol/cholestanol independently of obesity. In conclusion, cholesterol metabolism was altered already from subjects with impaired fasting glucose. Upregulated cholesterol synthesis was associated with peripheral insulin resistance independent of obesity.

Fig. 1.

The correlation between serum lathosterol/sitosterol (10² μg/μg) reflecting cholesterol metabolism and the Matsuda index reflecting peripheral insulin sensitivity in 781 middle-aged men, aged from 45 to 70 years. r = −0.457, P < 0.001, All: y = −0.650×+2.254. NTG: y = −0.586×+2.206; IFG: y = −0.302×+1.349; IGT: y = −0.802×+2.298; DM: y = −0.534×+1.597. NGT, normal glucose tolerance; IFG, impaired fasting glucose; IGT, impaired glucose tolerance; T2D,= type 2 diabetes.