Purpose: Few studies have analyzed the association between ambient temperature/air pollutants and inpatient admissions for major depressive disorder (MDD). The aim of this population-based study was to investigate the association between inpatient admissions due to MDD and ambient temperature/air pollutants over a period of 7 years. Methods: Among 185,689 patients identified from the Psychiatric Inpatient Medical Claim dataset of Taiwan from 2000 to 2005, 41,312 MDD patients were included in this study. Any psychiatric hospitalization of these patients from January 1, 2006 to September 30, 2012 was recorded. Meteorological and air pollutant data were collected from the databases of the Central Weather Bureau and Environmental Protection Administration, respectively. Results: Females had higher odds of MDD admission. Admission rates proportionally increased with elevated ambient temperature, PM_(2.5) levels, and NO_x levels for same-day, 7-day lagged, and 14-day lagged exposures. Higher NO_x was positively associated with admission rate. Compared with lower levels of PM_(2.5), higher levels of PM_(2.5) had a protective effect on MDD admissions for 7-day and 14-day lagged exposures. There was a positive relationship between the interactions of both high levels of PM_(2.5) and NO_x and MDD admissions after controlling for other factors. Conclusion: More research is needed to identify potential environmental risks to decrease MDD admissions.
