Incidence and risk factors for mild cognitive impairment: a population-based three-year follow-up study of cognitively healthy elderly subjects

BACKGROUND: Mild cognitive impairment (MCI) has attracted considerable interest as a potential predictor of Alzheimer's disease (AD). Both the apolipoprotein E (ApoE) epsilon4 allele and vascular factors have been associated with a higher risk for AD, recently they have also been linked to the risk of MCI. OBJECTIVES: To estimate the incidence of MCI among cognitively healthy elderly subjects during a 3-year follow-up, and to evaluate the impact of demographic and vascular factors as well as the ApoE epsilon4 allele on the conversion to MCI. METHODS: At baseline, the cognitive abilities of 806 out of 1,150 eligible subjects (aged 60-76 years) from a population-based sample were examined. Cognitively intact subjects (n = 747) were followed for an average of 3 years. RESULTS: 66 subjects (8.8%) had converted to MCI. The global incidence rate of MCI was 25.94/1,000 person-years. Persons with higher age (OR 1.08, 95% CI 1.01-1.16), ApoE epsilon4 allele carriers (OR 2.04, 95% CI 1.15-3.64) and persons with medicated hypertension (OR 1.86, 95% CI 1.05-3.29) were more likely to convert to MCI than those individuals of lower age and without an ApoE epsilon4 allele or medicated hypertension. Persons with high education (OR 0.79, 95% CI 0.70-0.89) were less likely to convert to MCI than persons with low or no education. In subjects with both the ApoE epsilon4 allele and medicated hypertension, the crude OR for conversion was 3.92 (95% CI 1.81-8.49). In subjects with cardiovascular disease, the crude OR for conversion was 2.13 (95% CI 1.26-3.60). Gender, elevated blood pressure, diabetes or cerebrovascular disease had no significant effect on the conversion to MCI. CONCLUSION: Higher age, the presence of at least one ApoE epsilon4 allele and medicated hypertension are independent risk factors, but high education is a protective factor for MCI. The results suggest that vascular factors may have an important role in the pathogenesis of MCI.