Sex differences in the association between proinsulin and intact insulin with coronary heart disease in nondiabetic older adults: the Rancho Bernardo Study.

BACKGROUND Insulin or insulin resistance is considered a coronary heart disease (CHD) risk factor, but proinsulin may have a stronger association with CHD than insulin. The role of sex differences in this association is unclear. We examined the cross-sectional association of proinsulin and insulin with CHD in older men and women without diabetes. METHODS AND RESULTS A cross-sectional study of community-dwelling men (n=554) and women (n=902), 50 to 97 years of age, without diabetes by history or oral glucose tolerance test, was done between 1992 and 1996; plasma levels of intact insulin, proinsulin, and C-peptide were measured by radioimmunoassay. Based on questionnaire, medical history, or ECG abnormalities, 25% of men (n=136) and 24% of women (n=214) had prevalent CHD. All insulin variables were positively correlated with CHD risk factors. Compared with those without CHD, men and women with CHD had significantly higher levels of proinsulin. Women but not men with CHD also had higher levels of C-peptide and fasting and postchallenge insulin. Only proinsulin was significantly and independently associated with prevalent CHD in both men (OR=2.41, 1.42 to 4.11) and women (OR=1.80, 1.22 to 2.64) (adjusted for age, body mass index, systolic blood pressure, and HDL cholesterol). Similar analyses for fasting and postchallenge intact insulin and for C-peptide showed that among these three variables, only postchallenge insulin was significantly associated with CHD, and only in women. CONCLUSIONS In older nondiabetic men and women, proinsulin was more strongly and consistently associated with CHD than was intact insulin.