Low fasting serum insulin and dementia in nondiabetic women followed for 34 years

Objective: A previous study reported a U-shaped association between fasting insulin and dementia in a 5-year follow-up of a male cohort, which was now re-investigated in a representative population of women followed over 34 years, and taking into account the incidence of diabetes. Methods: Fasting values for insulin and glucose were obtained from serum samples in 1212 non-diabetic women aged 38-60 at the 1968 baseline. Risk of dementia was assessed by Cox proportional hazard regression adjusting for insulin, glucose, and other covariates, and, in a second model, after censoring for incident cases of diabetes. Incident diabetes was considered as a third endpoint, for comparison with dementia. Results: Over 34 years, we observed 142 incident cases of dementia. The low tertile of insulin displayed excess risk for dementia, hazard ratio (HR) = 2.34, 95% confidence interval = (1.52, 3.58), compared to the medium tertile, but the high tertile of insulin did not, HR = 1.28 (0.81, 2.03). These...