Seasonality of hospitalization for schizophrenia and mood disorders: A single-center cross-sectional study in China.

BACKGROUND: Seasonal patterns exist in many disorders and even serve as potential drivers of some disorders, but in schizophrenia and affective disorders, there is no uniform conclusion on the seasonal pattern.

METHODS: A total of 100,621 inpatients were surveyed in this study over 16 years, and 21,668 inpatients were ultimately included in the count after standard exclusion criteria were applied.

RESULTS: There was an uneven seasonal distribution of mental illness admissions (χ2 = 48.299, df = 18, P < .001). The peak of schizophrenia admissions occurred in the winter and the trough in the spring (52.6 % vs 50 %, P < .05). The peaks for depression and bipolar disorder were in the fall and spring, respectively, while the troughs were in the winter and fall, respectively (24.7 % vs 21.7 %, P < .05; 15.2 % vs 13.2 %, P < .05). Admissions for childhood mood disorders peaked in the fall (P < .05). We also found that the length of stay was also correlated with the season of admission, and that this seasonal fluctuation was not consistent across male and female populations.

LIMITATIONS: To avoid the effect of repeated hospitalizations, we maintained a registry of each patient's first admission only, which also resulted in our inability to explore the seasonal pattern of each disease recurrence at the individual level.

CONCLUSIONS: We found that the seasonal distribution of psychiatric admissions was not uniform. And there was also an uneven seasonal distribution of length of stay for patients admitted in different seasons. This may imply that certain environmental factors that vary with the seasons are potential drivers of mental illness.