Abstract
Abstract Background and aims Dementia is a growing public health concern due to the increasing numbers of people affected, and the associated societal and economic impact. Dementia is related to a range of potentially modifiable risk factors including loneliness and depressive symptoms. This paper aimed to use data from the English Longitudinal Study of Ageing (ELSA) to evaluate the longitudinal relationships between loneliness, depressive symptoms and risk of dementia. Methods Data came from ELSA (waves 2-8), and the sample comprised of 5467 participants aged 50 years or over who did not have dementia at baseline. Loneliness was measured using the 3 item UCLA loneliness scale and depressive symptoms were calculated using the Center for Epidemiologic Studies Depression tool. A range of sociodemographic, physiological risk factors and health behaviours were measured at baseline. Cox Proportional Hazards Regression analyses were used to estimate longitudinal relationships. Results The main analysis found a significant relationship between depressive symptoms and risk of dementia which was attenuated after controlling for physiological risk factors and health behaviours (HR 1.03, 95% CI 0.96-1.56). The main analysis also indicated an independent relationship between loneliness and risk of dementia in a most adjusted model (HR 1.08, 95% CI 1.00-1.17), however further analyses demonstrated that the interaction between loneliness and depressive symptoms together increase risk of dementia, and loneliness was only related to an increased risk of dementia when depressive symptoms were present. Conclusions This study supports that depression is a risk factor for dementia, and that this relationship is well explained by physiological risk factors. This study also found that there is an affective component related to the increased risk of dementia associated with loneliness. This has implications in the way that loneliness is investigated and conceptualised. Further research is needed to explore pathways which might explain these relationships.