High plasma insulin is associated with lower LDL cholesterol in elderly individuals

To investigate possible relationships between plasma low density lipoprotein (LDL) cholesterol and fasting plasma insulin in the elderly, cross-sectional random samples of age cohorts (65, 75, 80 and 85 years, n = 1188, M/F 38/62 percent) were studied in the neighbouring cities of Helsinki and Vantaa, Finland. Plasma total and high density lipoprotein (HDL) cholesterol, plasma triglycerides, blood glucose and plasma insulin were measured after an overnight fast. LDL cholesterol was calculated using the Friedewald equation. Statistical analyses were performed separately in subjects with non-insulin-dependent diabetes mellitus (NIDDM, n = 219) and non-diabetic subjects (n = 969). Comparison of lipid levels by insulin quartile (I < 7.4 IU/1, II 7.4-10.0, III 10.1-15.0, IV > 15.0) showed that total and LDL cholesterol decreased in the highest insulin quartile (P = 0.003). This trend prevailed after adjustments for age, gender, body mass index, blood glucose and serum triglycerides, and it was significant also in normotriglyceridemic (serum triglycerides <2.3 mmol/l) subjects. Furthermore, the association between high insulin and lower cholesterol was seen in normoglycemic (fasting blood glucose <6.7 mmol/l) and diabetic subjects. Lower LDL cholesterol in elderly subjects with higher fasting insulin may reflect poor health or a 'harvesting' effect, but the results may also be due to effects of insulin on LDL catabolism and/or cholesterol absorption.