My research examines the association between the altitude of the participant's residence and the presence of an actively depressed mood, explicitly examining whether individuals experienced a depressed mood during the four weeks before an interview assessment during a population-based epidemiological survey. I explore this association at the community and individual levels. Additionally, I investigated whether using coca leaves might moderate the observed relationship between altitude and depressed mood. In this dissertation, my epidemiological estimates are from nine yearly cross-sectional epidemiological studies conducted in Peru. These studies encompassed 15 regions in Peru and included community residents in areas situated at different altitudes above sea level. The main results of my dissertation can be summarized as follows: Study 1: At the community level (i.e., district level), those populations located at higher altitudes also had higher estimated prevalence proportions of depressed mood. These estimates are from a comparison of direct estimates of survey data analysis, using standardized estimates (i.e., with direct adjustment for age and sex), and finally using estimators corresponding to the Small Area Estimation methodology (i.e., Fay-Herriot model). Study 2: Estimated at the individual level, an association between altitude and depressed mood was found and remained stable after logistic regression models adjusted for other covariates of interest (i.e., age, sex, mother tongue, marital status, and length of residency). By stratifying the analysis according to the length of stay in the current community, the findings suggested a causal possibility. The estimated effect of high altitude on a person's mood may be more pronounced after a minimum of two years of residing at such heights. Study 3: In assessing coca-leaf consumption as a moderator of the altitude-depression association, I found an absence of evidence that coca-leaf product use in the month before the survey modifies the relationship between altitude and depressed mood. In fact, if anything, individuals who use coca might be more likely to experience active depressive moods, even at higher altitudes. However, the study's cross-sectional nature prevents the evaluation of the temporal aspect of this association. As for limitations, the cross-sectional character of the data, with no specification of the age of onset of depressed mood relative to the time of residency at the altitude of the current dwelling, is a crucial limitation. Also, this study did not evaluate other community characteristics that might be covarying with the altitude-depression relationship. This new evidence on the altitude-depression association draws attention to a need for more research along these lines. The research might gain increased importance during the 21st century intervals of global warming and associated climate change. Given that an estimated 500 million individuals reside in high-altitude regions around the globe, the association that links altitude and the occurrence of depressed mood deserves continuing attention in our epidemiological research projects.
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