Abstract
BackgroundNearly 800,000 suicides occur worldwide annually and suicide rates are increasing faster than population growth. Unfortunately, the pathophysiology of suicide remains poorly understood, which has hindered suicide prevention efforts. However, mechanistic clues may be found by studying effects of seasonality on suicide and other mortality causes. Suicides tend to peak in spring-summer periods and nadir in fall-winter periods while circulatory system disease-related mortality tends to exhibit the opposite temporal trends. This study aimed to determine for the first time whether monthly temporal cross-correlations exist between suicide and circulatory system disease-related mortality at the population level. If so and if common biological factors moderate risks for both mortality types, such factors may be discoverable and utilized to improve suicide prevention.MethodsWe conducted time series analyses of monthly mortality data from northern (England and Wales, South Korea, United States) and southern (Australia, Brazil) hemisphere countries during the period 2009–2018 (N = 41.8 million all-cause mortality cases). We used a Poisson regression variant of the standard cosinor model to determine peak months of mortality. We also estimated cross-correlations between monthly mortality counts from suicide and from circulatory system diseases.ResultsSuicide and circulatory disease-related mortality temporal patterns were negatively correlated in Australia (− 0.32), Brazil (− 0.57), South Korea (− 0.32), and in the United States (− 0.66), but no temporal correlation was discernable in England and Wales.ConclusionsThe negative temporal cross-correlations between these mortality types we found in 4 of 5 countries studied suggest that seasonal factors broadly and inversely moderate risks for circulatory disease-related mortality and suicide, but not in all regions, indicating that the effect is not uniform. Since the seasonal factors of temperature and light exert opposite effects on suicide and circulatory disease-related mortality in several countries, we propose that physiologically-adaptive circulatory system responses to heat and light may increase risk for suicide and should be studied to determine whether they affect suicide risk. For example, heat and light increase production and release of the bioactive gas nitric oxide and reduce circulatory system disease by relaxing blood vessel tone, while elevated nitric oxide levels are associated with suicidal behavior, inverse effects that parallel the inverse temporal mortality patterns we detected.
Highlights
800,000 suicides occur worldwide annually and suicide rates are increasing faster than population growth
We report for the first time using population data from multiple countries, that negative temporal cross-correlations exist between mortality resulting from suicide and from circulatory system-related diseases in four of five countries studied
These findings suggest that seasonal factors broadly and inversely moderate temporal patterns for suicide and circulatory system disease-related mortality to different extents in each country
Summary
800,000 suicides occur worldwide annually and suicide rates are increasing faster than population growth. Important clues to better understanding suicide pathophysiology may be found by considering research on seasonal variations in mortality patterns for suicide and for circulatory system diseases, which account for 1.4 and 32%, respectively, of worldwide all-cause mortality [1]. Peaks and nadirs in suicide deaths tend to occur in spring-summer and fall-winter periods, respectively [10, 11]. Mortality peaks and nadirs for diseases of the circulatory system tend to occur in fall-winter and spring-summer periods, respectively [12, 13]. Physiological mechanisms activated by seasonal factors that moderate suicide risk, some of which could overlap with those driving circulatory system morbidity and mortality, may be discoverable and exploited to better identify those at increased risk for suicide
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