Frailty Components as Moderators of the Subjective Cognitive Decline–Depressive Symptoms Association: A Sex-Stratified Population-Based Study

Background/Objective: Subjective cognitive decline (SCD) and depressive symptoms are among the most prevalent mental health concerns in older populations, and SCD has been consistently associated with depressive symptoms. However, whether individual Fried Frailty Phenotype (FFP) components modify the association between SCD and depressive symptoms, and whether these moderating patterns differ across sex, has yet to be empirically examined. This study aimed to examine whether individual FFP components moderate the association between SCD and depressive symptoms in older adults, using sex-stratified analyses. Methods: Using data from the Korea National Health and Nutrition Examination Survey, complex sample general linear models were applied to 1404 adults aged 65 years and older. Five FFP components were tested as moderators separately for men and women. Results: SCD was positively associated with depressive symptoms in both sexes. Unintentional weight loss (B = 0.43, p = 0.009) and exhaustion (B = 0.18, p = 0.037) were significant moderators in men. Among women, muscle weakness (B = −0.26, p = 0.002), slowness (B = 0.18, p = 0.020), and unintentional weight loss (B = −0.34, p = 0.022) were identified as significant moderators. Additionally, a formal interaction test indicated a statistically significant sex difference only for unintentional weight loss. Conclusions: The findings underscore the value of examining frailty at the individual-component level, rather than as a single construct, offering a more nuanced understanding of the association between SCD and depressive symptoms through sex-stratified analyses.