Social class and the risk of dementia: A systematic review and meta-analysis of the prospective longitudinal studies.

Background: The association between belonging to a disadvantaged socio-economic status or social class and health outcomes has been consistently documented during recent decades. However, a meta-analysis quantifying the association between belonging to a lower social class and the risk of dementia has yet to be performed. In the present work, we sought to summarise the results of prospective, longitudinal studies on this topic.

Methods: We conducted a systematic review and meta-analysis of prospective, longitudinal studies measuring the association between indicators of social class and the risk of all-cause/Alzheimer's dementia. The search was conducted in four databases (Medline, Embase, Web of Science and PsychInfo). Inclusion criteria for this systematic review and meta-analysis were: (a) longitudinal prospective study, (b) aged ⩾60 years at baseline, (c) issued from the general population, (d) no dementia at baseline and (e) mention of social class as exposure. Exclusion criteria were: (a) study of rare dementia types (e.g. frontotemporal dementia), (b) abstract-only papers and (c) articles without full text available. The Newcastle-Ottawa scale was used to assess the risk of bias in individual studies. We calculated the overall pooled relative risk of dementia for different social class indicators, both crude and adjusted for sex, age and the year of the cohort start.

Results: Out of 4548 screened abstracts, 15 were included in the final analysis (76,561 participants, mean follow-up 6.7 years (2.4-25 years), mean age at baseline 75.1 years (70.6-82.1 years), mean percentage of women 58%). Social class was operationalised as levels of education, occupational class, income level, neighbourhood disadvantage and wealth. Education (relative risk (RR)=2.48; confidence interval (CI) 1.71-3.59) and occupational class (RR=2.09; CI 1.18-3.69) but not income (RR=1.28; CI 0.81-2.04) were significantly associated with the risk of dementia in the adjusted model. Some of the limitations of this study are the inclusion of studies predominantly conducted in high-income countries and the exclusion of social mobility in our analysis.

Conclusions: