The effect of heat waves on mental health in a temperate Australian city

Abstract

Objective: The goal of this study was to identify mental, behavioral, and cognitive disorders that may be triggered or exacerbated during heat waves, predisposing individuals to heat-related morbidity and mortality.

Design: Using health outcome data from Adelaide, South Australia, for 1993-2006, we estimated the effect of heat waves on hospital admissions and mortalities attributed to mental, behavioral, and cognitive disorders. We analyzed data using Poisson regression accounting for overdispersion and controlling for season and long-term trend, and we performed threshold analysis using hockey stick regression.

Results: Above a threshold of 26.7 degrees C, we observed a positive association between ambient temperature and hospital admissions for mental and behavioral disorders. Compared with non-heat-wave periods, hospital admissions increased by 7.3% during heat waves. Specific illnesses for which admissions increased included organic illnesses, including symptomatic mental disorders; dementia; mood (affective) disorders; neurotic, stress related, and somatoform disorders; disorders of psychological development; and senility. Mortalities attributed to mental and behavioral disorders increased during heat waves in the 65- to 74-year age group and in persons with schizophrenia, schizotypal, and delusional disorders. Dementia deaths increased in those up to 65 years of age.

Conclusion: Our results suggest that episodes of extreme heat pose a salient risk to the health and well-being of the mentally ill.

Relevance to clinical or professional practice: Improvements in the management and care of the mentally ill need to be addressed to avoid an increase in psychiatric morbidity and mortality as heat waves become more frequent.

Keywords: dementia; heat waves; mental health; psychiatric; schizophrenia; temperature; weather.

Figure 1

Calculated point estimates (IRRs and 95% CIs) of the risk during heat waves compared with non-heat-wave periods, of hospital admission for mental, behavioral, and cognitive disorders. Abbreviations: Alzh, Alzheimer’s disease; Child, behavioral and emotional disorders with onset usually occurring in childhood and adolescence; Dem, dementia; Dev, disorders of psychological development; Mood, mood (affective) disorders; Neur, neurotic, stress-related, and somatoform disorders; Org, organic, including symptomatic, mental disorders; Pers, disorders of adult personality and behavior; Phys, behavioral syndromes associated with physiological disturbances and physical factors; Ret, mental retardation; Schiz, schizophrenia, schizotypal, and delusional disorders; Sen, senility; Subst, disorders due to psychoactive substance use.

Figure 2

Exposure–response relationships between T_max and hospital admissions for mental disorders for (A) All MBDs; (B) organic, including symptomatic, mental disorders; (C) dementia; (D) neurotic, stress-related, and somatoform disorders; (E) disorders of psychological development; and (F) senility. Data were smoothed using a lowess smoother, bandwidth = 0.8.