Impact of social network on cognitive performances and age-related cognitive decline across a 20-year follow-up

Background: The objective of this study was to investigate the relationship between social network and cognitive decline, taking into account the potential bias of reverse causality. Methods: The study sample comprised 2055 elderly participants without dementia. We assessed baseline social functioning across four variables: size of social network, satisfaction with relationships, perception of being understood, and participation in social activities. A neuropsychological battery was proposed at baseline and repeated throughout follow-up. Linear mixed models were used to investigate the relationship between social network and baseline cognitive performances and cognitive decline during the 20-year follow-up. Results: When controlling for the reverse causality bias by excluding participants who developed dementia during the study follow-up and after adjusting for covariates, the results showed that better social functioning at baseline was associated with better initial performances in the Isaacs Set Test and the Wechsler Paired Associate Test. However, there was no significant association with further cognitive decline. By contrast, when the bias of reverse causality was not controlled for (i.e. no exclusion of participants who developed dementia), the association between social network and global cognitive decline measured by MMSE was found to be statistically significant. Conclusion: With the opportunity to exclude participants who developed dementia, and the particularly long follow-up of participants, we were able to investigate the relationship between social networks and age-related cognitive decline with a minimization of reverse causality bias. The results suggest that even though higher social functioning is concomitantly associated with better cognitive performances, it may not prevent subsequent decline.