Background: Suicide rates vary with important cycles in life, according to scientific findings and sometimes only according to lay beliefs. This paper reviews empirical studies on the association between suicides and a selection of cycles in life (the course of day, week, year, and life, menstrual cycle, and the moon phases).
Methods: Non-systematic review with a selection of key-papers and recent reviews, and analyses of Austrian daily suicide data from 1970-2017.
Results: For the time of day, suicides occur slightly more frequently from morning to mid-day. However, among people awake, suicides peak during nighttime. For the course of the week, suicide rates increase on Mondays and decrease on weekends. Similarly, there are more suicides after major holidays. For the course of the year, suicide rates increase in spring/summer, decrease in December, are lowest on Christmas, peak on New Year's Day, and go back to about the yearly average thereafter. With respect to the life cycle, suicide rates are lowest in children and highest in elderly people, especially in men. Suicide rates increase during menstruation but not in the pre-menstruation phase. Suicide rates do not vary with moon-phases.
Conclusions: There is robust evidence that suicide rates vary with some cycles in human life, such as day of the week, seasons and holidays, and there is some evidence that suicides vary with time of day and the menstrual cycle. Some of the associations seem counter-intuitive but can be explained with theories of suicides and related psychosocial mechanisms (e.g., the Broken Promise Effect). Since the effects are mostly small, findings cannot easily be translated into clinical practice but they enhance our understanding of suicides nonetheless.