What exactly does your study show?
Ana Vicedo: Our study indicates that ambient temperature could influence the risk of hospitalizations due to mental disorders. We were able to show that higher ambient temperatures are associated with an increased risk of hospitalization due to mental disorders. The study is based on daily admission figures of the University Psychiatric Hospital of Bern between 1973 and 2017, with a total number of nearly 90’000 hospitalizations. We combined this 45-year data series with high-resolution local temperature data.
Is the link between rising temperatures and the incidence of mental illness a new observation?
Marvin Bundo: Yes, recent epidemiological studies indicate that elevated ambient temperatures are associated with a higher risk of mental health outcomes such as hospitalizations, emergency room visits, and suicide. However, this study included nearly 90,000 mental health hospitalizations over a longer period of time compared to previous studies. To our knowledge, this is the first study to investigate this association in Europe and in a country with a temperate climate such as Switzerland.
What does medicine already know about the link between heat stress and mental illness?
Thomas Müller: We know that people with mental disorders are fundamentally more vulnerable to various stressors. They are less able to cope with heat, and there are also indications that patients with psychoses, for example, are more sensitive to heat on the one hand due to their illness, but also due to the medication they take. All in all, this leads to an increased risk of new episodes of the disease or a worsening of the condition.
There also seems to be a connection between rising temperatures and the frequency of suicides ...
Thomas Müller: Yes. There is evidence from some studies that the risk of suicide or suicide attempts increases during periods of unusual heat. One of these studies was able to demonstrate this influence in suicides in different countries and cities, including 8 cities in Switzerland. Other studies give indications of an increased risk of suicide attempts. And our own, but yet unpublished study, also find an indication of this in Switzerland.
Your study states that heat does not have the same negative effect on all mental illnesses ...
Marvin Bundo: The association seems to be influenced by the psychiatric sub diagnosis. Patients with developmental disorders and schizophrenia seemed to be most affected in this study. This finding can be explained, for example, due to the fact that many patients with developmental disorders – for example autism - can be hyposensitive to external environmental hazards such as extreme temperatures. Furthermore, heat has been shown to inhibit learning in schools and could, therefore, worsen further the condition of children with learning disabilities.
Couldn't other reasons than rising temperatures be responsible for the increase in admissions of psychiatric patients?
Ana Vicedo: We used the state-of-the-art methods in climate change epidemiology to provide robust conclusions on the role of ambient temperature. In particular, factors changing in time at a slower peace such as changes in hospitalization rates would not affect our estimates since their influence is removed by the design of the study. Likewise, we argue that our findings are not biased by other environmental factors, such as other weather conditions or air pollution, since in our analysis these variables seemed to not confound the association.
You call for psychiatric patients, as a vulnerable population group, to be better protected from the consequences of climate change. What does that mean in concrete terms?
Thomas Müller: Patients with mental illnesses are, as already mentioned, more vulnerable. They have fewer resources to protect themselves against stressors. We must therefore ensure that people with these illnesses in particular can be better protected during heat waves. Nowadays, the focus during heat waves is on the elderly. We need to extend this to people with mental illnesses. And we need to study the link between this vulnerability and mental disorders more specifically and intensively.
What is new about your study is not least that it was carried out in cooperation between climatologists and experts in epidemiology, psychiatry. How exactly did this cooperation take place?
Thomas Müller: The collaboration was exciting in every respect. It arose from my observation of conspicuous accumulations in connection with unusual weather patterns of admissions or empty beds in the University Psychiatric Services in Bern. Ultimately, this led to contact with the team of climatologists and epidemiologists. A truly translational approach with a view beyond one's own disciplines ...
Ana Vicedo: ... The collaboration was exciting in every respect. It arose from my observation of conspicuous accumulations in connection with unusual weather patterns of admissions or empty beds in the University Psychiatric Services in Bern. Ultimately, this led to contact with the team of climatologists and epidemiologists. A truly translational approach with a view beyond one's own disciplines.
About the interviewees
Dr. Ana M. Vicedo-Cabrera is an environmental epidemiologist who leads the research group on Climate Change and Health, jointly established by the OCCR and the Institute for Social and Preventive Medicine at the University of Bern.
Marvin Bundo is a Ph.D. student in the research group on Climate Change and Health. His doctoral thesis focuses on the effects of climate change on mental health in Switzerland.
Prof. Dr. med. Thomas Mülleris a Professor of Psychiatry at the Medical faculty of the University of Bern. He was the head of Outpatient Department of the University Hospital of Psychiatry and is now the Medical Director at Privatklinik Meiringen.
Ambient temperature and mental health hospitalizations in Bern, Switzerland: A 45- year time-series study, PLoS ONE 16(10): e0258302. https://doi.org/10.1371/journal.pone.0258302