Relationship between serum insulin-like growth factor-1 levels and Alzheimer's disease and vascular dementia

Objectives: To determine whether decreased serum insulin-like growth factor-1 (IGF-1) levels could be a risk factor for dementia in older people. Design: Case control study. Setting: Showa University Karasuyama Hospital, Tokyo, Japan. Participants: A total of 436 Japanese elderly subjects: 106 patients with Alzheimer's disease (AD), 103 patients with vascular dementia (VaD), and 227 age-matched controls without dementia. Mesurements: Serum concentrations of IGF-1 and atherogenic lipoproteins, carotid artery intima-media thickness (IMT), and plaques were determined. Results: Mini-Mental State Examination (MMSE) scores were positively correlated with serum IGF-1 concentrations as well as mean blood pressure or body mass index and were negatively correlated with age, serum low-density lipoprotein cholesterol and lipoprotein(a) concentrations, and carotid IMT. Serum IGF-1 concentrations had a significant inverse correlation with carotid IMT. Analysis across the IGF-1 quartiles revealed a threshold effect of low IGF-1 on MMSE score in subjects with the IGF-1 levels of 140 ng/mL or less (50% percentile) versus those with IGF-1 levels greater than 140 ng/mL. Multiple logistic regression concerning AD and VaD retained serum IGF-1 concentrations of 140 ng/mL or less and carotid IMT of 0.9 mm or more. Patients with AD and VaD had significantly lower IGF-1 concentrations and greater mean IMT than nondemented controls. Conclusion: These results suggest that decreased serum IGF-1 level and the progression of carotid atherosclerosis could play a role as independent risk factors for dementia.