Background Being married is associated with healthier lifestyle behaviours and lower mortality and may reduce risk for dementia due to life-course factors. We conducted a systematic review and meta-analysis of studies of the association between marital status and the risk of developing dementia. Methods We searched medical databases and contacted experts in the field for relevant studies reporting the relationship, adjusted for age and sex, between marital status and dementia. We rated methodological quality and conducted random-effects meta-analyses to summarise relative risks of being widowed, divorced or lifelong single, compared with being married. Secondary stratified analyses with meta-regression examined the impact of clinical and social context and study methodology on findings. Results We included 15 studies with 812 047 participants. Compared with those who are married, lifelong single (relative risk=1.42 (95% CI 1.07 to 1.90)) and widowed (1.20 (1.02 to 1.41)) people have elevated risk of dementia. We did not find an association in divorced people. Further analyses showed that less education partially confounds the risk in widowhood and worse physical health the elevated risk in lifelong single people. Compared with studies that used clinical registers for ascertaining dementia diagnoses, those which clinically examined all participants found higher risk for being unmarried. Conclusions Being married is associated with reduced risk of dementia than widowed and lifelong single people, who are also underdiagnosed in routine clinical practice. Dementia prevention in unmarried people should focus on education and physical health and should consider the possible effect of social engagement as a modifiable risk factor.

Hospitalisation is often harmful for people with dementia and results in high societal costs, so avoidance of unnecessary admissions is a global priority. However, no intervention has yet reduced admissions of community-dwelling people with dementia. We therefore aimed to examine hospitalisation rates of people with dementia and whether these differ from people without dementia and to identify socio-demographic and clinical predictors of hospitalisation. We searched MEDLINE, Embase, and PsycINFO from inception to 9 May 2019. We included observational studies which (1) examined community-dwelling people with dementia of any age or dementia subtype, (2) diagnosed dementia using validated diagnostic criteria, and (3) examined all-cause general (i.e. non-psychiatric) hospital admissions. Two authors screened abstracts for inclusion and independently extracted data and assessed included studies for risk of bias. Three authors graded evidence strength using Cochrane’s GRADE approach, including assessing for evidence of publication bias using Begg’s test. We used random effects meta-analysis to pool estimates for hospitalisation risk in people with and without dementia. We included 34 studies of 277,432 people with dementia: 17 from the USA, 15 from Europe, and 2 from Asia. The pooled relative risk of hospitalisation for people with dementia compared to those without was 1.42 (95% confidence interval 1.21, 1.66) in studies adjusted for age, sex, and physical comorbidity. Hospitalisation rates in people with dementia were between 0.37 and 1.26/person-year in high-quality studies. There was strong evidence that admission is associated with older age, and moderately strong evidence that multimorbidity, polypharmacy, and lower functional ability are associated with admission. There was strong evidence that dementia severity alone is not associated. People with dementia are more frequently admitted to hospital than those without dementia, independent of physical comorbidities. Future interventions to reduce unnecessary hospitalisations should target potentially modifiable factors, such as polypharmacy and functional ability, in high-risk populations.

There is need to identify targets for preventing or delaying dementia. Social contact is a potential target for clinical and public health studies, but previous observational studies had short follow-up, making findings susceptible to reverse causation bias. We therefore examined the association of social contact with subsequent incident dementia and cognition with 28 years’ follow-up. We conducted a retrospective analysis of the Whitehall II longitudinal prospective cohort study of employees of London civil service departments, aged 35–55 at baseline assessment in 1985–1988 and followed to 2017. Social contact was measured six times through a self-report questionnaire about frequency of contact with non-cohabiting relatives and friends. Dementia status was ascertained from three linked clinical and mortality databases, and cognition was assessed five times using tests of verbal memory, verbal fluency, and reasoning. Cox regression models with inverse probability weighting to account for attrition and missingness examined the association between social contact at age 50, 60, and 70 years and subsequent incident dementia. Mixed linear models examined the association of midlife social contact between 45 and 55 years and cognitive trajectory during the subsequent 14 years. Analyses were adjusted for age, sex, ethnicity, socioeconomic status, education, health behaviours, employment status, and marital status. Of 10,308 Whitehall II study participants, 10,228 provided social contact data (mean age 44.9 years [standard deviation (SD) 6.1 years] at baseline; 33.1% female; 89.1% white ethnicity). More frequent social contact at age 60 years was associated with lower dementia risk (hazard ratio [HR] for each SD higher social contact frequency = 0.88 [95% CI 0.79, 0.98], p = 0.02); effect size of the association of social contact at 50 or 70 years with dementia was similar (0.92 [95% CI 0.83, 1.02], p = 0.13 and 0.91 [95% CI 0.78, 1.06], p = 0.23, respectively) but not statistically significant. The association between social contact and incident dementia was driven by contact with friends (HR = 0.90 [95% CI 0.81, 1.00], p = 0.05), but no association was found for contact with relatives. More frequent social contact during midlife was associated with better subsequent cognitive trajectory: global cognitive function was 0.07 (95% CI 0.03, 0.11), p = 0.002 SDs higher for those with the highest versus lowest tertile of social contact frequency, and this difference was maintained over 14 years follow-up. Results were consistent in a series of post hoc analyses, designed to assess potential biases. A limitation of our study is ascertainment of dementia status from electronic health records rather than in-person assessment of diagnostic status, with the possibility that milder dementia cases were more likely to be missed. Findings from this study suggest a protective effect of social contact against dementia and that more frequent contact confers higher cognitive reserve, although it is possible that the ability to maintain more social contact may be a marker of cognitive reserve. Future intervention studies should seek to examine whether improving social contact frequency is feasible, acceptable, and efficacious in changing cognitive outcomes.