Association between solar insolation and a history of suicide attempts in bipolar I disorder
Introduction
Patients with bipolar disorder have a very high risk of suicidal behavior with about 1/3 of patients attempting suicide at least once (Novick et al., 2010; Tondo et al., 2016). A complex interplay of diverse factors contribute to suicidal behavior, including cultural, socioeconomic, genetic, stressful life experiences, the course of bipolar disorder and physical health (Schaffer et al., 2015; Tondo et al., 2016). Research has also found a relation between environmental factors and suicide rates. Many international studies of the general population have reported a seasonal variation in completed suicide and suicide attempts with peak rates in spring or summer (Barker et al., 1994; Christodoulou et al., 2012; Coimbra et al., 2016; Dixon and Kalkstein, 2018; Woo et al., 2012; Galvão et al., 2018; Odagiri et al., 2011; Petridou et al., 2002). Seasonality in suicide may be associated with a prior psychiatric diagnosis (Postolache et al., 2010; Reutfors et al., 2009; Rocchi et al., 2007).
This association of suicide rates with environmental factors is of considerable concern since circadian rhythm disturbances are found in many psychiatric illnesses, including bipolar disorder (Carr et al., 2018; Jagannath et al., 2013; Jones and Benca, 2015; Logan and McClung, 2019). Although strongly linked, the relationship between circadian disruption and the development and course of bipolar disorder is complex, bidirectional and not understood (Bechtel, 2015; Harvey, 2008; Ketchesin et al., 2018; Logan and McClung, 2019; McCarthy, 2018; McCarthy and Welsh, 2012; Oliveira et al., 2018). Circadian disturbances that occur frequently in bipolar disorder include alterations to the sleep/wake cycle and daily hormonal secretion, and misalignments between external time and social activities (Abreu and Bragança, 2015; Bellivier et al., 2015; Talih et al., 2018; Wirz-Justice, 2006). While symptoms of circadian disruption are most prominent during episodes of mania or depression, many occur when patients are euthymic including sleep disturbances, irregular social rhythms, preference for evening activities, and abnormalities in melatonin secretion (Alloy et al., 2017; Melo et al., 2017; Ng et al., 2015; Soreca, 2014; Takaesu, 2018). About one-fourth of patients with bipolar disorder experience a seasonal pattern in episode type, with manic episodes peaking in spring/summer and depression in winter (Geoffroy et al., 2014, 2015). Hospitalizations for mania are more numerous in spring/summer than in winter (Aguglia et al., 2017; Geoffroy et al., 2014). Some treatments for bipolar disorder may directly or indirectly target the circadian system (Bellivier et al., 2015; McClung, 2007).
Analyzing a large global sample, we previously found a strong, inverse relation between the maximum monthly increase in solar insolation in springtime and the age of onset of bipolar I disorder (Bauer et al., 2012, 2014; 2017), where solar insolation is defined as the amount of electromagnetic energy from the Sun striking a surface area of the Earth, expressed in kilowatt hours/square meter/day (kWh/m2/day) (Stackhouse et al., 2018).
This replicated finding suggests that some patients with bipolar disorder may have difficulty adjusting to an environmental challenge to the circadian system. The purpose of this exploratory post-hoc analysis was to investigate if solar insolation was associated with a history of suicide attempts in patients with bipolar I disorder, using the data previously collected.
Section snippets
Data collection
Data were collected between 2010 and 2016 by researchers at 50 sites in 32 countries to study the effects of solar insolation on the age of onset of bipolar disorder (Bauer et al., 2017). The database contains information on 7392 patients of which 5536 patients have a diagnosis of bipolar I disorder based on DSM-IV criteria. Data were obtained by patient questioning, record review or both. Study approval, including for data collection, was obtained according to local requirements, using local
Patient demographics and locations
There were 5536 patients with a diagnosis of bipolar I disorder in the database, of which a history of suicide was available for 3897 patients. However, only 3365 patients were included in the analysis after eliminating those who did not have all five variables in the final model. All 532 patients eliminated for not having the five variables were missing only one variable. Of the 532 patients, all but 2 were missing a history of alcohol or substance abuse data. Of the 3365 patients in the final
Discussion
In this global sample, 31% of the patients with bipolar I disorder have a history of suicide attempt, similar to prior research (Tondo et al., 2016; Vieta et al., 2018). The ratio of the mean winter solar insolation/mean summer solar insolation was inversely associated with an increased risk of suicide attempts. Patients from locations with smaller differences between mean winter and summer insolation such as near the equator (high ratio) had fewer suicide attempts, while those from locations
Conclusion
In conclusion, this exploratory analysis suggests that living in locations with large changes in solar insolation between winter and summer may be associated with increased suicide attempts in patients with bipolar disorder. Given the increased recognition of the importance of sunlight on human behavior and the frequent presence of circadian rhythm dysfunction in bipolar disorder, more knowledge of the relation of solar insolation to suicide attempts is needed.
Conflicts of interest
All authors declare that they have no conflict of interest.
Contributors
All authors contributed to and approved the final manuscript. Authors MB and TG designed the study and provided a draft manuscript. Authors MA, OAA, EA, RA, YA, CB, RB, BTB, CBP, FB, RHB, MB, YB, SB, HBO, TDB, JC, EYWC, MDZ, SD, MD, BE, AF, KNF, MAF, AGP, JFG, PG, HH, CH, ETI, SJ, FK, MK, SK, SK, BK, TLK, RK, MK, BL, ML, ERL, UL, RWL, CLJ, GM, MM, WM, MMC, IM, FMU, MYM, SM, GM, EM, AAM, RM, SVM, FN, RKN, FGN, REN, CO, AO, YO, HOS, UO, YPR, MP, MP, FDRP, DQ, RR, NR, MSR, AR, PR, JKR, KS, BSR,
Role of the funding source
The funding sources had no involvement in the study design, data collection, analysis, interpretation, report writing or the decision to submit for publication.
Acknowledgement
Michael Berk is supported by an NHMRC Senior Principal Research Fellowship (APP1059660 and APP1156072). Ole A Andreassen, Thomas D Bjella and Ingrid Melle are supported by Research Council of Norway (223273) and KG Jebsen Stiftelsen. Ravi Nadella has received funding from the Accelerator program for Discovery in Brain disorders using Stem cells (ADBS), jointly funded by the Department of Biotechnology, Government of India, and the Pratiksha trust. Biju Viswanath has received funding by
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