Investigation of risk factors associated with the development of depressive symptoms in healthy subjects exposed to long-term stress: A prospective study of the Japanese Antarctic research expedition wintering party.

Background: Stressors induce depression together with parenting experienced in childhood, personality traits, and sleep. In this study, we investigated factors associated with the development of depression in a long-term stressful environment, namely, the Antarctic Research Expedition wintering party, by comparing 2 groups, the depression and nondepression groups.

Methods: A self-administered questionnaire was used to survey 91 members of the Japanese Antarctic Research Expedition who spent winters in the Antarctic base. Psychological evaluations of depression, anxiety, and sleep were performed using a questionnaire every 3 months during the participants' stay in Antarctica. The primary endpoint was the occurrence of minor or major depression, as evaluated by the PHQ-9 score.

Results: Participants with a PHQ-9 score of 5 or more during their stay in Antarctica were defined as the depression group (25 subjects), and participants with a PHQ score of 4 or less were defined as the nondepression group (43 subjects). Compared with the nondepression group, the depression group had significantly higher scores for predeparture PHQ-9, state and trait anxiety, sleep disturbance, and neuroticism. Multivariable logistic regression analyses showed that higher predeparture scores of subthreshold depressive symptoms and neuroticism were found to be significant predictors of the occurrence of depression during their stay in Antarctica.

Conclusions: This study prospectively showed that subthreshold depressive symptoms and neuroticism, which were suggested as risk factors in previous studies, were confirmed to be risk factors for depression. The results of our study are expected to contribute to the understanding of depression in harsh environments.