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Background Identifying modifiable lifestyle correlates of cognitive decline and risk of dementia is complex, particularly as few population-based longitudinal studies jointly model these interlinked processes. Recent methodological developments allow us to examine statistically defined sub-populations with separate cognitive trajectories and dementia risks. Methods Engagement in social, physical, or intellectual pursuits, social network size, self-perception of feeling well understood, and degree of satisfaction with social relationships were assessed in 2854 participants from the Paquid cohort (mean baseline age 77 years) and related to incident dementia and cognitive change over 20-years of follow-up. Multivariate repeated cognitive information was exploited by defining the global cognitive functioning as the latent common factor underlying the tests. In addition, three latent homogeneous sub-populations of cognitive change and dementia were identified and contrasted according to social environment variables. Results In the whole population, we found associations between increased engagement in social, physical, or intellectual pursuits and increased cognitive ability (but not decline) and decreased risk of incident dementia, and between feeling understood and slower cognitive decline. There was evidence for three sub-populations of cognitive aging: fast, medium, and no cognitive decline. The social-environment measures at baseline did not help explain the heterogeneity of cognitive decline and incident dementia diagnosis between these sub-populations. Conclusions We observed a complex series of relationships between social-environment variables and cognitive decline and dementia. In the whole population, factors such as increased engagement in social, physical, or intellectual pursuits were related to a decreased risk of dementia. However, in a sub-population analysis, the social-environment variables were not linked to the heterogeneous patterns of cognitive decline and dementia risk that defined the sub-groups. Electronic supplementary material The online version of this article (doi:10.1186/s12889-015-2426-6) contains supplementary material, which is available to authorized users.

Background Diabetes is common in the older population and is increasing. Glycated hemoglobin (HbA1c) is an indicator of average blood glucose concentration over the past three months. The HbA1c test is currently one of clinical methods used to check diabetes control. Recent studies have suggested diabetes is a risk factor for dementia, cognitive dysfunction and physical disability. In addition, there have reported the relationship between HbA1c and mortality on all cause, cardiovascular disease and cognitive function, but few studies have investigated the relationship concentrating on the older population. The aim of this study is to investigate the association between the level of HbA1c and mortality from all causes, incident cardiovascular disease, cognitive decline and physical disability in people aged 65 and over in England and Wales. Methods 1139 men and women aged 69 years and over who were participants in a ten year population based ageing multi-centre, longitudinal study who had HbA1c measurements after 5–6 years of follow up. All participants were flagged for death notification including causes at the Office of National Statistics. Information on health including vascular conditions, cognitive status, physical function and dementia were available from the study both before and after the HbA1c measurement. Survival analyses and logistic regression were conducted. Results Mortality from all causes, cardiovascular and ischaemic heart disease increased with increasing HbA1c. Participants with diagnosed diabetes or who had HbA1c≥ 7% but no self-reported diabetes had increased mortality risk from all causes and cardiovascular diseases. The respondents in the group HbA1c ≥7% who had not been diagnosed with diabetes had a significantly higher risk (odds ratio = 4.8 95% CI: 1.1 to 21.6) of developing dementia. Individuals who had self-reported diabetes but a HbA1c level 1c Conclusion The findings support previous reports that bio-markers of glucose metabolism are associated with long term outcomes, such as mortality and dementia.

Background Population ageing over the first half of this century is likely to lead to dramatic increases in the prevalence of dementia. This will affect all regions of the world, but particularly developing regions. Dementia projections have been used extensively to support policy. It is therefore important these projections are as accurate as possible. Discussion In this paper we provide a commentary on studies projecting the future prevalence of dementia for the world or for individual continents. We identify some important limitations of the methods used in published projections and provide recommendations to improve the accuracy of future projections, and allow for the checking of the accuracy of the predictions. Summary Accurate projections of dementia incidence, at both the global and local level, are essential for healthcare planners.

BACKGROUND: An association between depressive symptoms and features of built environment has been reported in the literature. A remaining research challenge is the development of methods to efficiently capture pertinent environmental features in relevant study settings. Visual streetscape images have been used to replace traditional physical audits and directly observe the built environment of communities. The aim of this work is to examine the inter-method reliability of the two audit methods for assessing community environments with a specific focus on physical features related to mental health. METHODS: Forty-eight postcodes in urban and rural areas of Cambridgeshire, England were randomly selected from an alphabetical list of streets hosted on a UK property website. The assessment was conducted in July and August 2012 by both physical and visual image audits based on the items in Residential Environment Assessment Tool (REAT), an observational instrument targeting the micro-scale environmental features related to mental health in UK postcodes. The assessor used the images of Google Street View and virtually "walked through" the streets to conduct the property and street level assessments. Gwet's AC1 coefficients and Bland-Altman plots were used to compare the concordance of two audits. RESULTS: The results of conducting the REAT by visual image audits generally correspond to direct observations. More variations were found in property level items regarding physical incivilities, with broad limits of agreement which importantly lead to most of the variation in the overall REAT score. Postcodes in urban areas had lower consistency between the two methods than rural areas. CONCLUSIONS: Google Street View has the potential to assess environmental features related to mental health with fair reliability and provide a less resource intense method of assessing community environments than physical audits.