|dc.description.abstract||Mental health is one important aspect of a healthy life. Emerging evidence has shown that the total ambient environment is shaping human brain health, which may further lead to adverse population mental health. In the United States (U.S.), about one in five adults are living with a mental illness and about 5.2% of all U.S. adults have been diagnosed with a serious mental illness that often requires hospitalization or advanced medical care services in the lifetime.(1) The existing mental health crisis in the U.S. society requires better research evidence to identify more related risk factors that are intervenable in the population scale. Ambient exposure may be one of them.
Although related evidence is rising, most of the existing epidemiological studies primarily focused on one specific ambient exposure, largely on particulate matter and temperature with limited follow-up periods. Much is still unknown about the impact of gaseous pollutants and other climatic conditions on population mental/psychiatric health. Most of the existing epidemiological studies used monitored air pollutants data at the city or county levels for the urban populations, leading to potential exposure measurement error for different residential geographical locations and limited generalizability. It is still not clear what underlying demographical and contextual factors drive the association heterogeneities in different sub-populations, across different age, sex, personal and community socioeconomic status. Model confounding control is often insufficient for mental health related outcomes.
This dissertation attempted to address these research gaps. We began by studying the short-term associations between increased exposure to air pollution and temperature levels, and psychiatric hospitalization risk in a case-crossover setting among the U.S. nationwide Medicare participants. This work discovered that short-term exposure to elevated levels of PM2.5, NO2 and cold season ambient temperature was significantly associated with increased risk of psychiatric hospitalization in the older adults. Moving on, in the second hospitalization study for the U.S. general population, we further investigate the impact of long-term exposure to air pollution and several key climate conditions on the risk of population psychiatric hospitalization in a U.S. general population. Consistent with what we found in the first chapter, harmful associations were observed between increased exposure to air pollution, ambient temperature increase and increased total psychiatric hospitalization risk, with the most remarkable evidence in long-term exposure to elevated levels of NO2 and risk of getting psychotic disorder-related hospital admission. In addition, the above observed associations were especially strong in economically disadvantaged areas. Last, looking into the impact of ambient exposures on psychiatric symptoms in a longitudinal setting, the third chapter of this dissertation found exposure to gaseous air pollutants was associated with higher intensity of psychiatric symptoms among a cohort of older men, particularly in the more acute time windows and in communities with lower socioeconomic conditions.
This dissertation demonstrated that harmful ambient exposures, such as air pollution and ambient temperature increase, are associated with increased psychiatric hospitalization risk in the U.S. elderly population as well as the general population. The related findings have higher generalizability compared with the existing literature due to the wide coverage and long study periods. This work adds much to the existing literature evidence on air pollution, climate change and population mental health.||