Seasonality and suicide in Italy: Amplitude is positively related to suicide rates

BackgroundRecent studies have reported changes in the time patterns of suicide, with conflicting findings regarding the direction of these changes: data from Italy were investigated to evaluate the influence of recent social and medicine-related changes on the seasonality of suicides in the country.MethodsA total of 71 227 male suicides and 26 466 female suicides occurring in Italy from 1974 to 2003 were investigated with harmonic spectral analysis to extract their monthly seasonal dispersion by five-year intervals.ResultsThe suicide rates of both males and females showed a rising trend, with an evident peak in the 1987-1994 period and a decrease thereafter. Seasonality of suicides, with a clear peak in spring as against the other seasons, accounted for a statistically significant proportion of total variance: around 40% among males and 39% among females. Seasonality did not change across time in a relevant way; however, an anticipation of the peak was observed in both males and females over time, with amplitude increasing or decreasing as a function of yearly suicide rates.LimitationsData could not be analysed according to age or to the method of suicide, since this information was not available across the whole time interval.ConclusionThe seasonal effect on mortality by suicide is positively related to suicide rates, so much that changes in suicide rates over time correspond to changes in suicide seasonality.