Background: Links between fatigue and depressive symptoms in medically ill patients are well-documented; however, few studies controlled for illness severity. Obstructive sleep apnea (OSA) is a common, frequently devastating disease that often includes daytime sleepiness and fatigue. Fatigue is also a hallmark depressive symptom. We previously reported that depressive symptoms explained ten times the variance in fatigue in OSA patients as did OSA severity itself (respiratory disturbance index, oxyhemoglobin saturation). OSA severity explained 4.2% of variance in fatigue while depressive symptoms explained an additional 42.3%. Here, we report a replication of these findings in a new, independent sample.
Methods: 56 untreated OSA patients had their sleep monitored with polysomnography on the UCSD GCRC. Participants completed the Center for Epidemiologic Studies-Depression (CESD), Profile of Mood States (POMS) and Medical Outcomes Studies (MOS) surveys. Data were analyzed using hierarchical linear regression.
Results: OSA severity explained 13.4% (p=0.022) of variance in POMS fatigue while CESD scores explained an additional 24.5% (p<0.001). Results were robust to changes in the scales used to measure these constructs.
Limitations: Cross-sectional design precludes determination of direction of causality. Assessment of depressive symptoms and fatigue was based on validated self-report measures.
Conclusions: These results reaffirm that depressive symptoms are dramatically and independently associated with worse fatigue in OSA patients. While the independent contribution of OSA severity varied between studies, depressive symptoms were the strongest predictor of fatigue in both studies. Assessment and treatment of mood symptoms-not just treatment of OSA itself-might reduce fatigue in these patients.