BRIEF REPORT A Role of Sunshine in the Triggering of Suicide Eleni Petridou, 1,2 Fotios C. Papadopoulos, 1 Constantine E. Frangakis, 3 Alkistis Skalkidou, 1 and Dimitrios Trichopoulos 1,2 Abstract: Several reports indicate that suicide follows a sea- sonal pattern with a dominant peak during the month of maximum daylight. The purpose of this study was to evaluate the hypothesis that sunshine exposure may trigger suicidal behavior. We found a remarkably consistent pattern of season- ality with peak incidence around June in the northern hemi- sphere and December in the southern hemisphere. Moreover, there was a positive association between the seasonal ampli- tude of suicide (measured by relative risk) and total sunshine in the corresponding country. These findings indicate that sun- shine may have a triggering effect on suicide, and suggests further research in the field of sunshine-regulated hormones, particularly melatonin. (EPIDEMIOLOGY 2002;13:106 –109) Keywords: suicide, seasonality, sunshine, serotonin, melatonin, latitude. I t has been reported that the incidence of suicide reaches a peak during the early summer. 1,2 This find- ing has been very difficult to explain and, in fact, seems to be counterintuitive, given the impression of most people that their mood deteriorates during fall and winter. It has been suggested that sunshine exposure may affect suicide risk through regulation of serotonin 3,4 or melatonin 5 levels, but supportive empirical evidence is lacking. We have evaluated the hypothesis that sun- shine may trigger suicide by collecting data on the monthly distribution of suicide deaths in countries with reliable statistics and by estimating sunshine exposure during the corresponding months. Methods Data In order to insure reliable data, we have focused on countries-members belonging to the Organisation for Economic Co-operation and Development (OECD). A thorough Internet search was performed for each of the 29 OECD countries. No Internet site was found for Portugal and Poland. For the 27 remaining countries, e-mails were sent and on-line forms were submitted, some times more than once, to officials or webmasters responsible for the data. For four countries (Belgium, Ireland, Luxembourg, and the United Kingdom), an answer was received that the requested data were not available, whereas no answer was received from three countries (Italy, Korea, and Turkey). Thus, distribution of suicide deaths by month was sent from 20 OECD countries for a period covering 4 to 24 of the most recent years. For the calculation of sunshine during the months with the highest density of suicide deaths, we have retrieved data from two Internet sites. Daylight duration data for every country were retrieved from the Internet web site www.sunrisesunset.com. Total sunshine per month was calculated by multiplying total daylight du- ration during the particular month by the average frac- tion of time during the month that the sun was not obstructed by clouds. This fraction was derived using “WINDISP4,” a Map and Image Display and Analysis System which was downloaded from the Internet web site of the Food and Agriculture Organisation of the United Nations. All months were evaluated on an equal duration basis. Statistical Analysis Parameters of seasonality within countries were esti- mated using the Poisson regression variant of the circu- lar normal distribution 6 (appendix) which is an analog of the classic Edward’s procedure. This procedure effi- ciently estimates the month of peak suicide incidence, the relative risk of committing suicide during the month From the 1 Department of Hygiene and Epidemiology, Athens University Med- ical School, Athens, Greece; 2 Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA; and 3 Department of Biostatistics, School of Hygiene and Public Health, The Johns Hopkins University, Baltimore, MD. Address correspondence to: Dimitrios Trichopoulos, Professor of Epidemiology, Department of Epidemiology, Harvard School of Public Health, 677 Huntigton Ave, Boston, MA 02115; dtrichop@hsph.harvard.edu. Submitted November 13, 2000; final version accepted May 31, 2001. Copyright © 2001 by Lippincott Williams & Wilkins, Inc. 106