Variations in seasonal solar insolation are associated with a history of suicide attempts in bipolar I disorder
Authors: Bauer Michael , Glenn Tasha , Achtyes Eric D. , Alda Martin , Agaoglu Esen , Altınbaş Kürşat , Andreassen Ole A. , Angelopoulos Elias , Ardau Raffaella , Vares Edgar Arrua , Aydin Memduha , Ayhan Yavuz , Baethge Christopher , Bauer Rita , Baune Bernhard T. , Balaban Ceylan , Becerra-Palars Claudia , Behere Aniruddh P. , Behere Prakash B. , Belete Habte , Belete Tilahun , Belizario Gabriel Okawa , Bellivier Frank , Belmaker Robert H. , Benedetti Francesco , Berk Michael , Bersudsky Yuly , Bicakci Şule , Birabwa-Oketcho Harriet , Bjella Thomas D. , Brady Conan , Cabrera Jorge , Cappucciati Marco , Castro Angela Marianne Paredes , Chen Wei-Ling , Cheung Eric Y. Wo , Chiesa Silvia , Crowe Marie , Cuomo Alessandro , Dallaspezia Sara , Del Zompo Maria , Desai Pratikkumar , Dodd Seetal , Donix Markus , Etain Bruno , Fagiolini Andrea , Fellendorf Frederike T. , Ferensztajn-Rochowiak Ewa , Fiedorowicz Jess G. , Fountoulakis Kostas N. , Frye Mark A. , Geoffroy Pierre A. , Gonzalez-Pinto Ana , Gottlieb John F. , Grof Paul , Haarman Bartholomeus C. M. , Harima Hirohiko , Hasse-Sousa Mathias , Henry Chantal , Høffding Lone , Houenou Josselin , Imbesi Massimiliano , Isometsä Erkki T. , Ivkovic Maja , Janno Sven , Johnsen Simon , Kapczinski Flávio , Karakatsoulis Gregory N. , Kardell Mathias , Kessing Lars Vedel , Kim Seong Jae , König Barbara , Kot Timur L. , Koval Michael , Kunz Mauricio , Lafer Beny , Landén Mikael , Larsen Erik R. , Lenger Melanie , Lewitzka Ute , Licht Rasmus W. , Lopez-Jaramillo Carlos , MacKenzie Alan , Madsen Helle Østergaard , Madsen Simone Alberte Kongstad A. , Mahadevan Jayant , Mahardika Agustine , Manchia Mirko , Marsh Wendy , Martinez-Cengotitabengoa Monica , Martiny Klaus , Mashima Yuki , McLoughlin Declan M. , Meesters Ybe , Melle Ingrid , Meza-Urzúa Fátima , Ming Mok Yee , Monteith Scott , Moorthy Muthukumaran , Morken Gunnar , Mosca Enrica , Mozzhegorov Anton A. , Munoz Rodrigo , Mythri Starlin V. , Nacef Fethi , Nadella Ravi K. , Nakanotani Takako , Nielsen René Ernst , O‘Donovan Claire , Omrani Adel , Osher Yamima , Ouali Uta , Pantovic-Stefanovic Maja , Pariwatcharakul Pornjira , Petite Joanne , Pfennig Andrea , Ruiz Yolanda Pica , Pilhatsch Maximilian , Pinna Marco , Pompili Maurizio , Porter Richard , Quiroz Danilo , Rabelo-da-Ponte Francisco Diego , Ramesar Raj , Rasgon Natalie , Ratta-apha Woraphat , Ratzenhofer Michaela , Redahan Maria , Reddy M. S. , Reif Andreas , Reininghaus Eva Z. , Richards Jenny Gringer , Ritter Philipp , Rybakowski Janusz K. , Sathyaputri Leela , Scippa Ângela M. , Simhandl Christian , Severus Emanuel , Smith Daniel , Smith José , Stackhouse Paul W. , Stein Dan J. , Stilwell Kellen , Strejilevich Sergio , Su Kuan-Pin , Subramaniam Mythily , Sulaiman Ahmad Hatim , Suominen Kirsi , Tanra Andi J. , Tatebayashi Yoshitaka , Teh Wen Lin , Tondo Leonardo , Torrent Carla , Tuinstra Daniel , Uchida Takahito , Vaaler Arne E. , Veeh Julia , Vieta Eduard , Viswanath Biju , Yoldi-Negrete Maria , Yalcinkaya Oguz Kaan , Young Allan H. , Zgueb Yosra , Whybrow Peter C. 
Published: September 2021

Abstract
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.