Suicide rates rise as temperatures rise

Relation

Burke M, González F, Baylis P, et al. Higher temperatures are increasing suicide rates in the United States and Mexico. Nat Clim Chang. 2018;8(8):723-729.

Objective

To determine whether suicide, one of the leading causes of death worldwide, is systematically influenced by climatic conditions

Draft

Retrospective observational study

Participant

Documented populations of the United States and Mexico

Study parameters assessed

• Durchschnittliche monatliche Temperaturen – US-Daten, die von PRISM gesammelt wurden, einem hochauflösenden gerasterten Klimadaten; Mexikanische Daten, die aus ähnlichen gerasterten Klimadatensätzen gesammelt wurden
• Monatliche Selbstmordraten in mexikanischen und amerikanischen Bezirken – US-Raten, abgeleitet von der Multiple Cause-of-Death Mortality Database des National Vital Statistics System 23 (1968-2004); Mexikanische Daten des mexikanischen National Institute of Statistics and Geography (1990-2010)
• Prozentsatz der monatlichen Tweets mit depressiver Sprache – 622.749.655 geolokalisierte Twitter-Updates wurden auf „depressive Sprache“ gescannt; Monatlicher Prozentsatz von Tweets, die in den Untersuchungsgebieten (Landkreise und Gemeinden in den Vereinigten Staaten und Mexiko) geolokalisiert sind und Wörter enthalten, die als Ausdruck „depressiver Sprache“ gelten (z. Schläfrigkeit, Episoden, Müdigkeit, Angst, Einsamkeit, Übelkeit, Nervosität, schwere, Schlaf, Selbstmordgedanken, Selbstmord, gefangen)

Primary outcome measures

• Korrelation zwischen Änderungen der durchschnittlichen monatlichen Temperaturen (gemessen in Grad Celsius) und monatlichen Selbstmordraten
• Korrelation zwischen Änderungen der durchschnittlichen monatlichen Temperatur (gemessen in Grad Celsius) und Prozentsatz von Tweets mit depressiver Sprache

Key insights

The correlation between suicide rates and increases in ambient temperature was significant and robust. Each 1°C increase in average monthly temperature above average increased the monthly suicide rate by 0.68% (95% confidence interval [CI]: 0.53%–0.83%) in the United States (1968–2004) and 2.1% (95% CI: 1.2%–3.0%) in Mexico (1990–2010).

The correlation between depressive tweets and an increase in ambient temperature was significant.

Using 2 different methods to categorize tweets as depressive or not, there were 2 results, each significant. Each additional 1°C in monthly average temperature increased the odds of a tweet being “depressing” by 0.79% (95% CI: 0.23%-1.35%) by one method and by 0.36% (95% CI: 0.05%-0.68%). from another.

Practice implications

These statistical observational studies show a significant correlation between rising ambient temperatures and suicide rates in the United States and Mexico. Plotting “depressive language” on social media against ambient temperature over time also illuminates a possible contributing mechanism for the correlation: hotter weather correlates with individual psychological distress (depressive tweets), which is robustly associated with higher suicide rates.

Documenting a significant risk factor for suicide is important, but even more so when the risk factor is both predictable through models and continually increasing. This increased risk is non-specific, i.e. h. it affects not only those who already have mental health problems, but the entire population.

The implication for practitioners is that climate change itself, while outside the scope of treatment-based medicine, is nonetheless contributing to rising rates of mental health problems.¹Climate change poses a threat to mental health, both on large scales (displacement trauma, loss of homes and livelihoods) and on smaller scales (increased individual responsiveness to conditions according to the stress-diathesis model of mental illness).²Practitioners must be aware of the triggering effects of external conditions on the general population and those currently at risk of suicide and other mental health crises.

The study controlled for confounding parameters such as gun ownership, air conditioning ownership, baseline temperatures, gender, population size and others. Because the study results are so consistent across all socioeconomic groups in the United States, the researchers suggest that a physiological explanation for the correlation is likely. Study leader Burke explains that this “at least suggests that there is a plausible biological connection between temperature, thermoregulation, and the way the brain regulates its own emotions.”³

The implication for practitioners is that climate change itself, while outside the scope of treatment-based medicine, is nonetheless contributing to rising rates of mental health problems.

This study provides information for developing mitigation strategies for communities affected by the impacts of climate change. For a practitioner, a mitigation strategy for rising temperatures should include: 1) close monitoring of those at risk during periods of higher temperatures; 2) preventive/prophylactic treatment for people with a history of mental health problems in preparation for warmer temperatures; and 3) improved screening of the general population for mental health problems during periods of higher temperatures.

A possible intervention strategy could include the use of hydrotherapy to support the body's thermoregulation system. Hydrotherapy has been researched for mental regulation and described as a sedative and neuroleptic for schizophrenia⁴and as an antidepressant for severe depressive disorders.⁵Based on lead researcher Burke's hypothesis regarding temperature, thermoregulation and emotional state specifically related to suicide, cold exposure could help reduce symptoms and suicide risk from increasing ambient temperatures.