Purpose: Elevated insulin levels have been associated with cardiovascular disease, but the relationship of insulin with other risk factors and its position in the atherosclerotic pathway is uncertain. A cross-sectional study was conducted to determine whether insulin concentrations were associated with lipids and lipoproteins independently of adiposity and other cardiovascular risk factors.
Methods: Subjects included 3417 Japanese-American men from the Honolulu Heart Program who completed a follow-up examination between 1991 and 1993 and were 71-93 years of age. Men were categorized by quintiles of fasting and 2-hour insulin concentration.
Results: Age-adjusted mean high-density lipoprotein (HDL) cholesterol and triglyceride levels varied significantly across quintiles of fasting and 2-hour insulin (P < 0.001, tests for trend), but insulin was not related to total cholesterol and low-density lipoprotein (LDL) cholesterol. HDL cholesterol decreased from 59.3 to 43.7 mg/dL and triglycerides increased from 95.6 to 175.8 mg/dL comparing lowest to highest quintiles of fasting insulin, respectively. These associations were slightly stronger in lean than obese subjects and in nondiabetic versus diabetic individuals particularly for 2-hour insulin levels. Multiple linear regression analysis adjusting for several adiposity measures separately (body mass index (BMI), subscapular skinfold thickness, waist circumference, and waist/hip ratio) and other cardiovascular risk factors attenuated associations slightly but they still remained statistically significant. Estimated differences in HDL cholesterol across extreme quintiles of fasting insulin were reduced slightly from 15.6 mg/dL with adjustment for age to 12.5 mg/dL with adjustment for age and BMI, and to 11.3 mg/dL with adjustment for age, BMI, and cardiovascular risk factors.
Conclusions: Insulin concentration was strongly and independently associated with HDL cholesterol and triglycerides in this cohort of elderly Japanese-American men. Since this study was cross-sectional, further investigation is required to determine whether elevated insulin levels are causally related to dyslipidemia.