Fatigue or excessive daytime sleepiness: which is more closely related to depression?

This study investigated fatigue and excessive daytime sleepiness to determine which was more closely related to depression in the general population.

Participants were investigated across 15 South Korean districts. Excessive daytime sleepiness, fatigue, and depression were evaluated using the Epworth Sleepiness Scale (ESS), Fatigue Severity Scale (FSS), and Patient Health Questionnaire-9 (PHQ-9), respectively. Depression was defined as PHQ-9 ≥ 10. The authors classified the combination of excessive daytime sleepiness and fatigue as excessive daytime sleepiness with fatigue (E⁺F⁺, ESS ≥ 11, FSS ≥ 36), fatigue without excessive daytime sleepiness (E^-F⁺, ESS < 11, FSS ≥ 36), excessive daytime sleepiness without fatigue (E⁺F^-, ESS ≥ 11, FSS < 36), and no fatigue and excessive daytime sleepiness (E^-F^-, ESS < 11, FSS < 36).

Among 2,493 participants (1,257 women), mean age was 47.9 ± 0.3 years. The prevalence of depression, fatigue, and excessive daytime sleepiness was 8.4% (n = 210), 30.8% (n = 767), and 15.3% (n = 382), respectively. The frequency of the four categories with depression (vs. controls) was as follows.: E⁺F⁺ (n = 67, 31.9% vs. 7.3%) (P < 0.001), E^-F⁺ (n = 71, 33.8% vs. 20.3%) (P < 0.001), E⁺F^-( n = 16, 7.6% vs. 5.8%) (P = 0.294), and E^-F^- (n = 56, 26.7% vs. 66.6%) (P < 0.001). After adjusting for covariates, depression was associated with E⁺F⁺ (odds ratio, OR 8.804, 95% confidence interval (CI) 5.818-13.132), E^-F⁺ (OR 3.942, 95% CI 2.704-5.747), E⁺F^- (OR 2.812, 95% CI 1.542-5.131), and E^-F^- (reference). Additionally, we performed logistic regression according to two categories. There was no significant difference in the association of depression between E⁺F^- (reference) and E^-F⁺ (OR 1.399, 95% CI 0.760-2.575).

Although fatigue and excessive daytime sleepiness were associated with depression regardless of the presence of each other, we could not clarify which was more closely related to depression.