Frailty and depression: Reciprocal influences or common causes?

Previous research demonstrated substantial associations between frailty and depression in late life, but it remains unclear whether this relationship is best explained by reciprocal influences of these variables or by common causes. This study investigated the interdependencies between frailty and depression across time by examining cross-lagged effects within individuals, while accounting for variability in baseline levels and long-term development between individuals.We modeled longitudinal data from six panel waves gathered in the Survey of Health, Ageing and Retirement in Europe, covering a time period of up to 14 years. The total sample size was N = 58,152 individuals aged 50 years or older. Frailty was based on a deficit accumulation frailty index and depressive symptoms were measured with the EURO-D scale. We used a latent curve model with structured residuals for statistical analysis.The results did not demonstrate relevant cross-lagged effects of frailty and depression at the within-person level. However, within-person increases in frailty were accompanied by within-person increases in depression at the same point in time. At the between-person level, it showed that individuals with higher levels and steeper trajectories in frailty also tend to show higher levels and steeper trajectories in depression.These findings question the notion that frailty and depression reciprocally influence each other over the course of time, but rather indicate that frailty and depression might be both affected by common causes, in both the short and the long term.