Associations between social connections and cognition: a global collaborative individual participant data meta-analysis

Background Poor social connections (eg, small networks, infrequent interactions, and loneliness) are modifiable risk factors for cognitive decline. Existing meta-analyses are limited by reporting aggregate responses, a focus on global cognition, and combining social measures into single constructs. We aimed to investigate the association between social connection markers and the rate of annual change in cognition (ie, global and domain-specific), as well as sex differences, using an individual participant data meta-analysis. Methods We harmonised data from 13 longitudinal cohort studies of ageing in North America, South America, Europe, Africa, Asia, and Australia. Studies were eligible for inclusion if they had baseline data for social connection markers and at least two waves of cognitive scores. Follow-up periods ranged from 0 years to 15 years across cohorts. We included participants with cognitive data for at least two waves and social connection data for at least one wave. We then identified and excluded people with dementia at baseline. Primary outcomes were annual rates of change in global cognition and cognitive domain scores over time until final follow-up within each cohort study analysed by use of an individual participant data meta-analysis. Linear mixed models within cohorts used baseline social connection markers as predictors of the primary outcomes. Effects were pooled in two stages using random-effects meta-analyses. We assessed the primary outcomes in the main (partially adjusted) and fully adjusted models. Partially adjusted models controlled for age, sex, and education; fully adjusted models additionally controlled for diabetes, hypertension, smoking, cardiovascular risk, and depression. Findings Of the 40 006 participants in the 13 cohort studies, we excluded 1392 people with dementia at baseline. 38 614 individual participants were included in our analyses. For the main models, being in a relationship or married predicted slower global cognitive decline (b=0 center dot 010, 95% CI 0 center dot 000-0 center dot 019) than did being single or never married; living with others predicted slower global cognitive (b=0 center dot 007, 0 center dot 002-0 center dot 012), memory (b=0 center dot 017, 0 center dot 006-0 center dot 028), and language (b=0 center dot 008, 0 center dot 000-0 center dot 015) decline than did living alone; and weekly interactions with family and friends (b=0 center dot 016, 0 center dot 006-0 center dot 026) and weekly community group engagement (b=0 center dot 030, 0 center dot 007-0 center dot 052) predicted slower memory decline than did no interactions and no engagement. Never feeling lonely predicted slower global cognitive (b=0 center dot 047, 95% CI 0 center dot 018-0 center dot 075) and executive function (b=0 center dot 047, 0 center dot 017-0 center dot 077) decline than did often feeling lonely. Degree of social support, having a confidante, and relationship satisfaction did not predict cognitive decline across global cognition or cognitive domains. Heterogeneity was low (I-2=0 center dot 00-15 center dot 11%) for all but two of the significant findings (association between slower memory decline and living with others [I-2=58 center dot 33%] and community group engagement, I-2=37 center dot 54-72 center dot 19%), suggesting robust results across studies. Interpretation Good social connections (ie, living with others, weekly community group engagement, interacting weekly with family and friends, and never feeling lonely) are associated with slower cognitive decline. Copyright (c) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 license.

Automated summary

This study found that good social connections, including living with others, weekly community group engagement, weekly interaction with family and friends, and rarely feeling lonely, are associated with slower cognitive decline.