Exploring the bidirectional associations between loneliness and cognitive functioning over 10 years: the English longitudinal study of ageing

Background: As the population ages, cognitive decline and dementia have become major health concerns in the UK. Loneliness has been linked to cognitive decline, but the reverse causality of this association remains unclear. This study aims to examine whether there is a bidirectional relationship between loneliness and cognitive function in older English adults (age 50 years and over) over a 10-year follow-up. Methods: Data came from a nationally representative sample of 5885 participants in the English Longitudinal Study of Ageing (ELSA), free of stroke or dementia and followed every 2 years up to wave 7 (2014-15). At each wave, cognitive function was measured with word recall and verbal fluency tests, and loneliness was measured with the abridged version of the revised UCLA Loneliness Scale. Bivariate dual change score models were used to assess the multivariate associations between loneliness and cognitive function, used interchangeably as exposures and outcomes. Results: Greater loneliness at baseline was associated with poorer memory [beta intercept = -0.03, standard error (SE) = 0.01, P = 0.016] and verbal fluency (beta intercept = -0.01, SE = 001, P = 0.027) at baseline, and with a stronger linear rate of decline in both memory (beta linear slope = -0.07, SE = 001, P <= 0.001) and verbal fluency (beta linear slope = -0.09, SE = 0.03, P = 0.003) over a 10-year follow-up period, although the performance on verbal fluency did not change substantially on average over this period. We also found that higher baseline memory, but not verbal fluency, predicted a slower change in loneliness (beta linear slope = -0.01, SE = 001, P = 0.004) and that a linear decline in memory was associated with an acceleration in loneliness (b quadratic slope = -0.02, SE = 001, P <= 0.001) during follow-up. Conclusions: Higher loneliness is associated with poorer cognitive function at baseline and contributes to a worsening in memory and verbal fluency over a decade. These factors seem, however, to be partially intertwined, since baseline memory and its rate of decline also contribute to an increase in loneliness over time.