Abstract
Background Social health markers, including marital status, contact frequency, network size, and social support, have shown associations with cognition. However, the underlying mechanisms remain poorly understood. We investigated whether depressive symptoms and inflammation mediated associations between social health and subsequent cognition.
Methods In the English Longitudinal Study of Ageing (ELSA; n=7,136; aged 50+), we used four-way decomposition to examine to what extent depressive symptoms, C-reactive protein (CRP) and fibrinogen (assessed at an intermediate time point) mediated associations between social health and subsequent standardised cognition (verbal fluency, delayed and immediate recall) including cognitive change, with slopes derived from multilevel models (ELSA: 12-year slope). We examined whether findings replicated in the Swedish National Study of Aging and Care in Kungsholmen (SNAC-K; n=2,846; aged 60+; 6-year slope).
Findings We found indirect effects via depressive symptoms of network size, positive support and less negative support on subsequent verbal fluency, and positive support on subsequent immediate recall (pure indirect effect (PIE)=0.002 [0.000-0.003]). The positive support-verbal fluency mediation finding replicated in SNAC-K. Depressive symptoms partially mediated associations between less negative support and slower immediate (PIE=0.001 [0.000-0.002]) and delayed recall decline (PIE=0.001 [0.000-0.002]), and between positive support and slower immediate recall decline (PIE=0.001, [0.000-0.001]), which replicated in SNAC-K. We did not observe mediation by inflammatory biomarkers.
Interpretation Findings provide new insights into mechanisms linking social health with cognition, suggesting that associations between cognition and interactional aspects of social health in particular, such as social support, are partly underpinned by depressive symptoms.
Competing Interest Statement
The authors have declared no competing interest.
Funding Statement
This work was supported by the Social Health and Reserve in the Dementia patient journey (SHARED) SHARED Consortium, an EU Joint Programme Neurodegenerative Disease Research (JPND). The project is supported by Alzheimers Society (Ref:469) in the UK, by ZonMw/ JPND (733051082) in the Netherlands, by National Center for Research and Development in Poland, project number (NCBiR; JPND/06/2020) in Poland, by the National Health and Medical Research Council (NHMRC; APP1169489) in Australia. The English Longitudinal Study of Ageing was developed by a team of researchers based at University College London, NatCen Social Research, the Institute for Fiscal Studies, the University of Manchester, and the University of East Anglia. The data were collected by NatCen Social Research. The funding is currently provided by the National Institute on Aging (Ref: R01AG017644) and by a consortium of UK government departments: Department for Health and Social Care; Department for Transport; Department for Work and Pensions, which is coordinated by the National Institute for Health Research (NIHR, Ref: 198-1074). Funding has also been provided by the Economic and Social Research Council (ESRC). SNAC-K (http://www.snac.org) is financially supported by the Swedish Ministry of Health and Social Affairs; participating County Councils and Municipalities; the Swedish Research Council; and Swedish Research Council for Health, Working Life and Welfare. This project was funded by the Swedish Research Council for Health, Working Life, and Welfare (FORTE Grant No. 2018-01888 to AK Welmer).
Author Declarations
I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.
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ELSA data used in this study are available to download through the UK Data Service. SNAC-K data used in this study are available to researchers upon approval by the SNAC-K data management and maintenance committee. Applications for accessing these data can be submitted to Maria Wahlberg (Maria.Wahlberg@ki.se) at the Aging Research Centre, Karolinska Institutet, Stockholm, Sweden.
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Data Availability
ELSA data used in this study are available to download through the UK Data Service. SNAC-K data used in this study are available to researchers upon approval by the SNAC-K data management and maintenance committee. Applications for accessing these data can be submitted to Maria Wahlberg (Maria.Wahlberg@ki.se) at the Aging Research Centre, Karolinska Institutet, Stockholm, Sweden.