Symptom-specific links between depression and functional impairment in young adults

Depression is a leading cause of functional impairment among young adults, yet little is known about which specific symptoms most disrupt daily life. This study disaggregates depression at the symptom level to identify the most impairing features and examine their day-to-day associations with functioning. We analyzed data from two samples of young adults. First, in a nationally representative U.S. sample (N = 3118; CPES), we used weighted ordinal logistic regressions to examine how individual symptoms of depression predicted functioning. Second, in a 14-day daily diary study (N = 130), we used multilevel ordinal regressions to distinguish between- and within-person effects of symptom fluctuations on functional impairment. Across both datasets, fatigue was the most consistently impairing symptom (CPES: OR = 3.74; Daily Diary Between-Person [DDBP): OR = 8.61, ps < 0.001). Those experiencing elevated fatigue reported significant functional disruptions (Daily Diary Within-Person [DDWP]: OR = 2.29, p < .001). Anhedonia (CPES: OR = 2.10; DDWP: OR = 1.55, ps < 0.001), appetite/weight disturbance (CPES: OR = 2.16; DDBP: OR = 1.30; DDWP: OR = 1.87, ps < 0.001), and guilt (CPES: OR = 1.89; DDBP: OR = 1.71; DDWP: OR = 5.09, ps < 0.001) also showed robust associations with impairment in daily and lifetime contexts. Functional impairment in depression is not uniformly driven by total symptom burden but by specific highly impairing symptoms. Targeting impairing symptoms, especially fatigue, anhedonia, and guilt, may yield disproportionate gains in functional recovery. Results have the potential to inform tailored interventions for young adults.