Dr. Hans Knoblauch and Dipl.-Psych. Monika Stöhr, ZfP Südwürttemberg, Clinic for Psychiatry and Psychotherapy I at the University of Ulm, Department of General Psychiatry Wangen and Working Group on Climate Change and Mental Health: Heat waves affect people with mental illness in various ways. People with mental illness are actually a particularly vulnerable group, meaning they are more sensitive to heat and have difficulty regulating their body temperature. Certain mental illnesses, particularly schizophrenia, are associated with impaired thermoregulation. It is not yet clear what causes this impaired thermoregulation, but people with schizophrenia often have difficulty responding appropriately to heat and protecting themselves from it. This increases the risk of suffering from heat-related illnesses or dying in a heat wave.

The administration of psychotropic drugs such as antidepressants and antipsychotics further interferes with patients' thermoregulation. This occurs, for example, in the Hypothalamus of the brain or in the vascular tone, i.e., the width of the blood vessels. Psychotropic drugs interfere intensively with these systems and influence the body's ability to adapt to heat. Some psychotropic drugs also increase the photosensitivity of the skin, which can lead to skin damage occurring more quickly.

Various studies have found that suicides increase during heat waves, although the exact reason for this is not yet clear. People in a Manic episode, who have increased drive and are less critical during this phase, can overexert themselves during heat waves, not drink enough, and thus “overheat.” The same applies to people with dementia, who often drink too little anyway. This makes dehydration more likely and can lead to delirium, i.e., a severe state of confusion.

However, heat poses a health risk even for healthy people, especially those who work or exercise outdoors and are therefore particularly exposed. Even in healthy people, heat has a negative effect on various organ functions, including the brain. Studies have shown that concentration, memory, problem-solving, and decision-making abilities are reduced in hot weather. The exact effects of heat on the brain are currently being researched, with evidence suggesting, among other things, a disruption of the Blood-brain barrier and increased inflammatory processes.

Heat waves increase mortality, i.e., excess deaths due to heat compared to a reference period. In 2003, when Europe experienced an extreme heat wave, approximately 70,000 people died as a result of the heat. This was the largest natural disaster with the most deaths in Europe since 1908, the year of the Messina earthquake. It is now possible to calculate this increased mortality due to heat waves for each year. In 2022, there were approximately 60,000 heat-related deaths in Europe.

Heat waves are characterized by hot weather lasting not just a single day, but several days in a row. This period brings with it so-called tropical nights, during which it does not cool down properly and many people are unable to get the sleep and rest they need, which has a particularly adverse effect on people with mental illness.

The development of many mental illnesses is based on a vulnerability-stress explanatory model. This means that if a certain level of vulnerability is combined with sufficient stress, a new episode of mental illness can be triggered. Heat waves are a conceivable stress factor that increases psychological stress. However, there is still a great need for research on these issues.

The increased heat waves we are experiencing as a result of man-made climate change are also a cause of climate anxiety, climate concerns, or other climate-related emotions for people who have not previously suffered from mental illness. Solastalgia, or the painful longing for the home as it used to be, also plays a role here and can affect people of all ages.

Recorded by Stefanie Flunkert