Research reportExploring lag and duration effect of sunshine in triggering suicide
Introduction
Sunshine is considered to have a beneficial impact on mood and annual total sunshine has been shown to correlate with decreased suicide rates within countries, even after adjusting for confounding factors, such as sociodemographic factors (Nishimura et al., 2004, Preti, 1998, Souetre et al., 1990, Terao et al., 2002). The underlying pathophysiological mechanisms have not been elucidated, but sunshine has been reported to regulate specific hormonal and neurotransmitter levels, such as those of melatonin (Thalen et al., 1997), serotonin (Lambert et al., 2002) and cortisol (Wehr, 1998).
Interestingly, it has been consistently found that the incidence of suicide reaches a peak during spring or early summer (Bazas et al., 1979, Chew and McCleary, 1995, Kevan, 1980, Koskinen et al., 2002, Lambert et al., 2003, Lester and Frank, 1988, Partonen et al., 2004, Petridou et al., 2002, Preti and Miotto, 1998, Souetre et al., 1987). This finding is consistent across countries of both the northern and the southern hemisphere. Moreover, the magnitude of the suicide seasonality pattern, as expressed by the relative risk of committing suicide during the month of maximum versus minimum suicide frequency, is larger in countries with longer sunshine duration during the month of peak suicide incidence (Petridou et al., 2002). A most striking confirmation of this relation was evident in Greece, the country with the longest sunshine duration during the month of peak suicide incidence, which also exhibited the highest relative risk for committing suicide, a 50% increase during June (the month of peak suicide incidence) compared to December (Petridou et al., 2002).
Motivated by this finding, we have focused in this paper on Greek daily suicide and sunshine data, in order to: 1) explore the pattern of sunshine and suicide risk in a time frame of up to nine days before the suicide event, and investigate possible lag and duration parameters of sunshine in the triggering of the suicide, and 2) examine if the indicated pattern of sunshine and suicide risk can explain the monthly suicide variation.
Section snippets
Methods
Greek daily suicide data (ICD9: E950-E959) by gender for a ten-year period (1992–2001) was provided by the National Statistical Service of Greece, whereas daily data on solar radiance and temperature, for the same period, was acquired by the National Observatory of Athens. Given that Greece is a relatively small country with a total surface area of 134,000 km2, we used the latter data as a reasonable approximation of the solar radiance and temperature for the whole country. A total of 3717
Results
Fig. 1 presents daily frequency of suicide in the period 1992–2001 along with the variation of solar radiance and temperature during the same period. Both sunshine and temperature track in time with suicide, and thus controlling for temperature was necessary while performing the analyses. The average solar radiance for the years 1992–2001 peaked in June (26.87 MW/m2), while temperature in August (28.34 °C).
The risk of committing suicide was not associated with the solar radiance during the same
Discussion
Using daily solar radiance data, we found no association between sunshine and suicide risk during the same day of the suicide event. However, the past solar radiance on average was found to be related to an increased risk of suicide, indicating that the possible role of sunshine in the triggering of suicide is mediated through a mechanism with specific lag and duration effect.
Looking at both genders' risk of suicide, the sunshine exposure during the four days before the suicide event induced
Acknowledgments
The authors would like to thank the employees and organizations that provided the data used in this study and in particular the National Statistical Service of Greece and the National Observatory of Athens, as well as Professor George Chrousos and Professor Constantine Lyketsos for valuable comments on the manuscript.
Additional support by grant ES11659 from the National Institute for Environmental Health Sciences to Dr. Stevens and by grant EY 014314-01 from the National Eye Institute to Dr.
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