The cross-interaction between global and age-comparative self-rated health on depressive symptoms-considering both the individual and combined effects

Background: Numerous studies suggesting the relation between self-rated health (SRH) and depression have been reported using different measures. Therefore, we attempted to determine the difference in a depressive scale based on the different ways of measuring health between global SRH (SRH-global) and age-comparative SRH (SRH-age). Then, the combined effect of SRH-global and SRH-age on depressive symptoms was further investigated. Methods: Data from the Korean Longitudinal Study of Ageing (KLoSA) from 2008 to 2012 were analyzed. We divided the SRH-global and SRH-age into three levels-high, middle, and low-and combined each into nine new categories (SRH-combi). The Center for Epidemiologic Studies Depression Scale-10 Korean edition was used as the dependent variable. Results: A total of 8621 participant were enrolled at baseline. Individuals with lower SRHs-age compared to SRH-global tended to be more vulnerable to depressive symptoms. Low SRH-global with low (b = 0.654, p < 0.001) and middle SRH-age (b = 0.210, p = 0.003) showed association with higher CESD scores. Participants with high SRH-global × low SRH-age also had higher scores (b = 0.536, p < 0.001) compared to the "middle SRH-global × middle SRH-age" reference group. In contrast, among the middle (b = -0.696, p < 0.001) and high SRH-global (b = -0.545, p < 0.001) groups, participants with superior SRH-age had statistically lower CESD scores than the reference group. Conclusions: Although a sole general SRH has historically been widely used, it has been suggested that use of both general and age-comparative SRH would be more powerful and easy when we consider analyzing depression in old age.