Contrary to previous reports, head trauma was not a risk factor for AD, and smoking did not protect against AD. The association of family history with the risk of AD is weaker than previously estimated on the basis of cross-sectional studies. Female gender may modify the risk of AD, whether it be via biological or behavioral factors.

Dementia, a syndrome of cognitive decline severe enough to interfere with daily functioning and independent living, has been the subject of increasing focus for policymakers, civil organisations and multidisciplinary researchers. A substantial body of the most recent descriptive epidemiological research on dementia is allowing investigation of how prevalence and incidence might be changing across time. To establish clear trends, such comparisons need to be based on population-based studies using similar diagnostic and research methods over time. This review synthesises findings from nine prevalence trend studies and five incidence trend studies from western European countries (Sweden, Spain, UK, the Netherlands and France), the US, Japan and Nigeria. These population-based studies, apart from the Japanese study, have reported stable or declining prevalence and incidence and evidence of both inconsistent and similar changes in men and women within and across countries. No single risk or protective factor has been identified to fully explain these trends, but major societal changes in western societies and improvement in factors potentially associated with risk and protecting such as living conditions, higher education attainment and wider availability of healthcare might have favourably influenced multiple factors related to physical, mental and cognitive health across the lifecourse and could be responsible for this reduced risk of dementia in later life. Analytical epidemiologic approaches combined with translational neuroscientific research may provide a unique opportunity to explore underlying mechanisms of neuropathology and dementia in the general population. The findings from these studies provide robust evidence for developing fruitful avenues for prevention, diagnosis and treatment.

Compared with men, women have an increased risk for AD. There are no gender differences in risk for vascular dementia.

To obtain age- and gender-specific estimates of the prevalence of dementia in Europe and to study differences in prevalence across countries, we pooled and re-analysed original data of prevalence studies of dementia carried out in some European countries between 1980 and 1990. The study followed these steps: census of existing datasets, collection of data in a standardized format, selection of datasets suitable for comparison, comparison of age and gender patterns. From the 23 datasets of European surveys considered, 12 were selected for comparison. Only population-based studies in which dementia was defined by DSM-III or equivalent criteria and in which all subjects were examined personally were included. Studies in which institutionalized subjects were not investigated were excluded. Age- and gender-specific prevalences were compared within and across studies and overall prevalences were computed. Although prevalence estimates differed across studies, the general age- and gender-distribution was similar for all studies. The overall European prevalences for the five-year age groups from 60 to 94 years, were 1.0, 1.4, 4.1, 5.7, 13.0, 21.6 and 32.2%, respectively. In subjects under 75 years the prevalence of dementia was slightly higher in men than in women; in those aged 75 years or over the prevalence was higher in women. The prevalence figures nearly doubled with every five years of increase in age.