Long-term temperature exposure and depression incidence in the Nurses’ Health Study II, a U.S.-based prospective cohort

Background

While short-term temperature increases (e.g., daily) have been linked to higher rates of mental health hospitalizations, associations between longer-term temperature (e.g., annual) and mental health, particularly depression, are underexplored. The objective of this study was to examine the association between annual average temperature and depression incidence in a United States cohort.

Methods

After excluding all participants in the Nurses’ Health Study II who reported clinician-diagnosed depression or antidepressant use prior to 2001, we followed 39,339 participants across the study period between 2001 and 2019. We spatially linked 800 m2 annual average temperature estimates from the PRISM model to participants’ biennially-updated residential addresses. We defined incident depression as self-report of clinician-diagnosed depression or antidepressant use. We used Cox proportional hazards models to estimate adjusted hazard ratios and 95% confidence intervals for the association between annual average temperature and incident depression. Models included demographic and lifestyle characteristics as covariates. We performed sensitivity analyses to assess the robustness of the observed association to changes in outcome definition.

Findings

In a fully adjusted model, the hazard ratio for the association between annual average temperature and incident depression was 1·06 (1·02, 1·08) per interquartile range (4·9) increase. While this estimate was mildly attenuated in sensitivity analyses considering alternative outcome definitions, the adverse association remained robust.

Interpretation and funding

Our results suggest that sustained exposure to higher temperatures is associated with chronic depression and other mental health outcomes.