According to findings published in the journal Aging & Mental Health, depression and loneliness mutually influence each other in the short-term. But within a 6-year time lag, this reciprocal relationship is no longer significant.
Loneliness and depression tend to co-occur — people who are lonely often experience symptoms of depression and people who are depressed often feel lonely. But the nature of the relationship between the two mental states is unclear. Some studies have suggested that loneliness causes depression, others have suggested that depression causes loneliness, and still others have suggested a reciprocal relationship between the two.
Researcher Mohsen Joshanloo sought to gain insight into the relationship between loneliness and depression by employing a statistical technique called the Random-Intercept Cross-Lagged Panel Model (RI-CLPM). The RI-CLPM allows researchers to examine how two variables influence each other over time while separating between-person sources of variance from within-person sources of variance. In short, this technique would allow Joshanloo to isolate causal effects while ruling out trait-like stability in loneliness and depression.
Data was obtained from four waves of the German Ageing Survey (DEAS), a nationally representative survey of German adults over 40 years old. All waves included measures of depressive symptoms and loneliness. To explore the relationship between loneliness and depression over time, the study author tested two models. One model tested a 3-year lag and included waves 2008, 2011, and 2014. A second model tested a 6-year lag and included waves 2002, 2008, and 2014.
First, the 3-year lag model revealed an amount of within-person stability for both depression and loneliness. When a person deviated from their average levels of depression or loneliness at a given time point, they were likely to deviate from their average levels of these variables at the next time point, too. As Joshanloo reports, “if a person scores higher (or lower) than his/her expected loneliness and depression scores on one occasion, he/she is likely to score higher (or lower) than his/her expected scores on the next occasion as well.”
The 3-year lag model also revealed a reciprocal relationship between loneliness and depression, with either variable influencing the other at a later timepoint. Specifically, “if a person scores higher (or lower) than his/her expected score in one variable, he/she is likely to score higher (or lower) than his/her expected score in the other variable on the next occasion.” Since the RI-CLPM accounts for the stability of the variables, these findings suggest a reciprocal, causal relationship between loneliness and depression where “each of these variables is a risk factor for the other variable.”
However, at a 6-year lag, none of these paths were significant. There was instead a strong association between the trait-level aspects of depression and loneliness. The study author says this points to “the existence of stable genetic, developmental, and long-lasting lifestyle and situational factors that contribute to both variables.”
Joshanloo says these findings suggest that interventions that focus on long-term strategies and address stable symptoms of loneliness and depression will be more beneficial than interventions that focus on short-term changes. Since fluctuations from a person’s typical levels of loneliness and depression were not found to predict future fluctuations from that person’s typical levels of these variables beyond three years, interventions that are focused on short-term changes in depression and loneliness are unlikely to have a lasting effect on future levels of these variables.
“Making small and short-lived changes in behavior or mood is crucial but does not seem to be enough in chronic cases,” Joshanloo says. “In addition to symptom-focused and short-term interventions, interventions should also focus on stable characterological and/or contextual changes.”
The study, “The longitudinal interplay of depressive symptoms and loneliness: causal effects work in both directions and decay to zero before six years”, was authored by Mohsen Joshanloo.