Seasonal Changes in 24-h Patterns of Suicide Rates: a Study on Train Suicides in The Netherlands

It has been suggested that day length, or total hours of sunshine has an impact on suicide rates. If these environmental factors are involved, we would expect changes in daily pattern of suicide rates to occur over the year. To test this hypothesis, the 24-h patterns of suicide rate were investigated as a function of time of year. Daily patterns in train suicides show systematic variations of 2 kinds. First, independently of time of year, suicide rates at night drop to about 10% of their daytime values. Second, there are 2 daily peaks in the patterns which shift their timing over the year, with one peak occurring shortly after sunset, & the other one consistently occurring 9-10h earlier. Both peaks shift with the 5.5-h shift in sunset time. The consistency of the patterns suggests a strong environmental influence on train suicidal behaviour. (21 refs)