Seasonal Trends in Hospitalization of Attempted Suicide and Self-Inflicted Injury in United States Adults

Changes in meteorological conditions as near-term risk factors for suicide attempts

To evaluate the impact of acute meteorological changes (i.e., maximum temperature, humidity, wind speed, atmospheric pressure, cloud coverage, visibility, precipitation) as situational risk factors proximal (i.e., present in the hours directly preceding) to suicide attempts. Participants were 578 adult patients who were hospitalized within 24 h of a suicide attempt at the only Level 1 trauma hospital in the state of Mississippi. Participants completed a semi-structured interview to determine home address and exact timing of their suicide attempt. A within-person, case-crossover design was used with each patient serving as their own control. Meteorological variables were generated for the 6-hours preceding each patient's suicide attempt (case period) and corresponding hours the day prior (control period). Conditional logistic regression analyses were used to examine predictors of suicide attempts, and biological sex and season were evaluated as potential moderators. The presence of precipitation was associated with reduced odds of suicide attempts. Wind speed was marginally positively associated with suicide attempts among males, and visibility was positively associated with suicide attempts among females. Maximum temperature was positively associated with suicide attempts in the spring. Wind speed, visibility, maximum temperature, and precipitation (absence of) may represent situational risk factors for suicide attempts. Future studies should evaluate additional near-term situational risk factors and determine how to leverage this information to improve suicide risk management efforts to ultimately ameliorate the burden of suicide.

Variations in seasonal solar insolation are associated with a history of suicide attempts in bipolar I disorder

Background

Bipolar disorder is associated with circadian disruption and a high risk of suicidal behavior. In a previous exploratory study of patients with bipolar I disorder, we found that a history of suicide attempts was associated with differences between winter and summer levels of solar insolation. The purpose of this study was to confirm this finding using international data from 42% more collection sites and 25% more countries.

Methods

Data analyzed were from 71 prior and new collection sites in 40 countries at a wide range of latitudes. The analysis included 4876 patients with bipolar I disorder, 45% more data than previously analyzed. Of the patients, 1496 (30.7%) had a history of suicide attempt. Solar insolation data, the amount of the sun’s electromagnetic energy striking the surface of the earth, was obtained for each onset location (479 locations in 64 countries).

Results

This analysis confirmed the results of the exploratory study with the same best model and slightly better statistical significance. There was a significant inverse association between a history of suicide attempts and the ratio of mean winter insolation to mean summer insolation (mean winter insolation/mean summer insolation). This ratio is largest near the equator which has little change in solar insolation over the year, and smallest near the poles where the winter insolation is very small compared to the summer insolation. Other variables in the model associated with an increased risk of suicide attempts were a history of alcohol or substance abuse, female gender, and younger birth cohort. The winter/summer insolation ratio was also replaced with the ratio of minimum mean monthly insolation to the maximum mean monthly insolation to accommodate insolation patterns in the tropics, and nearly identical results were found. All estimated coefficients were significant at p < 0.01.

Conclusion

A large change in solar insolation, both between winter and summer and between the minimum and maximum monthly values, may increase the risk of suicide attempts in bipolar I disorder. With frequent circadian rhythm dysfunction and suicidal behavior in bipolar disorder, greater understanding of the optimal roles of daylight and electric lighting in circadian entrainment is needed.