Greece was found to have the highest seasonal suicide variation among 20 countries. The Victorian 8 and Greek 25 data have been examined previously to demonstrate the seasonality of suicides. For the daily analyses, we varied the daily sunlight exposure over 2550 sunlight exposure combinations corresponding to 1–50 days exposure window with lags of 0–50 days, allowing us to investigate previous claims that suicide and suicidal attempts were associated with lagged sunlight exposures. Briefly, we investigate within two cohorts (Greece: 1992–2001 Victoria, Australia: 1990–1998) the relationship between daily suicide rate and daily sunlight exposure, after removing seasonality via differencing. Finally, we address concerns that monthly data are too crude to disentangle such associations by attempting to validate a new publication by Vyssoki et al 26 that identified positive (ie, harmful) and negative (ie, protective) associations between daily suicide rate and sunlight. In addition, possible effect modification by season is investigated. We then examine the relationship between monthly sunlight and suicides, and observe what attenuation, if any, occurs after adjustment for month of year. We do so by investigating within three cohorts (Greece: 1992–2001 Victoria, Australia: 1990–1998 Norway: 1969–2009) the relationship between month of year (shifted for concordance between the northern and southern hemispheres) and monthly suicide rates, and what attenuation, if any, occurs after adjusting for different measures of sunlight exposure. The current study is the first to systematically attempt to disentangle the putative suicidogenic risk of seasonality from that of sunlight exposure using data from different sites with the same methodology. If such a suicidogenic relationship between sunlight and suicide were not present, then seasonality itself would remain related to suicide risk (with sunlight merely a very strong correlate of seasonality and confounder of the seasonality suicide relation). Exceptionally bright summers should, for example, be more lethal than overcast summers (and, barring any existing threshold, dark winters should be more protective than sunnier winters), and vice versa. If sunlight exposure causes suicides in susceptible persons, then a relationship should still be observable after seasonality has been taken into account. Null, 8, 14–17 beneficial, 18–23 harmful 24, 25 and mixed 26 associations have all been reported between sunlight and suicide after correcting for season. 1–7, 9 Lately, more studies apply seasonality corrections in their analyses, but still the results are inconclusive. The vast majority of older studies focusing on sunlight exposure and suicide, however, either ignore seasonality (ie, the month of the year) or adduce seasonality as evidence of a positive relationship between sunlight and suicide. 1–11 A frequent and plausible hypothesis to explain this relationship is that increased sunlight exposure alters biological mechanisms, possibly through the dysregulation of serotonin and/or melatonin production or metabolism. It has been noted broadly and frequently that suicides peak in spring and summer.
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