Review articleDo suicide attempts occur more frequently in the spring too? A systematic review and rhythmic analysis
Introduction
The World Health Organization estimates that 11.4 per 100.000 people (15.0 for males and 8.0 for females) committed suicide around the world in 2012 (WHO, 2014). For every completed suicide there are many more people who attempt suicide every day. Despite sharing the main feature which is the choice of taking their own lives, some studies have described differences between individuals who committed suicide and those who attempted suicide (Dejong et al., 2010, Fushimi et al., 2006, Giner et al., 2013, Malone et al., 2007, Parra Uribe et al., 2013, Younes et al., 2015). Persons who completed suicides were more likely to be male, older, less impulsive, have used more lethal methods, leave a suicide note and tended to be more depressed than low-lethality attempters. Suicide attempters predominantly self-poison, while completed suicides tended to perform hanging and use drugs or firearms. In despite of the proportion of completed suicides be twice higher in men than women, the rate of suicide attempts are more prevalent in women, particularly for young people (Hawton et al., 1998, Iribarren et al., 2000, Parra Uribe et al., 2013, Younes et al., 2015).
It is known that several risk factors act cumulatively to increase vulnerability to suicidal behavior. Some of them are associated with the health system and society, including difficulties in accessing health care, easy access to a mean of suicide such as pesticides or firearms and inappropriate media reporting that sensationalizes suicide. Many other risk factors were reported such as war and disasters, discrimination, sense of isolation, abuse, violence, conflicting relationships, previous suicide attempts, economic crisis, unemployment, chronic pain and a family history of suicide (WHO, 2014).
In despite of many variables that contribute to suicide, a seasonal pattern has been described. In fact, seasonality in completed suicide is a well-known phenomenon and an important topic in epidemiological studies (Ajdacic-Gross et al., 2010, Bridges et al., 2005, Christodoulou et al., 2012, Rasanen et al., 2002, Woo et al., 2012). Interestingly, studies report a higher frequency of suicide in spring and summer (Chew and McCleary, 1995, Christodoulou et al., 2012, Massing and Angermeyer, 1985, Partonen et al., 2004, Petridou et al., 2002, Preti and Miotto, 1998, Rocchi et al., 2007). In a worldwide cross-sectional data from 28 countries, a high frequency of suicides in spring was found (Chew and McCleary, 1995). In some studies, seasonal differences between males and females also have been found: males showing a single peak on spring, while females two peaks, in spring and autumn (Lester and Frank, 1988, Meares et al., 1981, Micciolo et al., 1989, Yip et al., 2000). The reason for this seasonal variation in completed suicides remains unclear.
Seasonal variation does not exist only in completed suicides. A similar pattern was also reported in attempted suicides (Yip and Yang, 2004). However, some studies described attempted suicide peaks in autumn and/or winter (Chien et al., 2013, Elisei et al., 2012, Pajoumand et al., 2012, Wenz, 1977a). Moreover, studies suggest that this seasonality might be a sex-specific phenomenon (Barker et al., 1994, Masterton, 1991, Mergl et al., 2010). Some researchers showed evidences of seasonality only in women (Barker et al., 1994, Jessen et al., 1999, Masterton, 1991). The reasons for this sex difference also remain unknown, but a possible explanation could be associated with the choice of the method used (Rock et al., 2005, Yip and Yang, 2004). There is no consensus in studies regarding seasonality of suicide attempts and, to our knowledge, no systematic review in this topic has been published.
The research question of this study was to know whether suicide attempts occur more frequently in the spring, such as already described for completed suicides. Thus, a systematic review of articles reporting suicide attempts over the year, in many countries, was conducted to investigate which season presents the higher incidence, considering potential interfering variables, such as sex, type of method used and source of data. Also, we performed a statistical analysis for seasonality with the collected data using applicable methods for rhythmic phenomena. The identification of a global seasonal profile in suicide attempts would provide knowledge to guide governments and public health organizations to develop strategies that can prevent suicide effectively.
Section snippets
Material and methods
The guidelines provided by the PRISMA statement (Moher et al., 2009) were closely applied. The searches were conducted in the following databases: Medline (Medical Analysis and Retrieval System Online) via PubMed (1966 to September 2014), ISI Web of Science (1945 to September 2014), LILACS (Literatura Latino-Americana e do Caribe em Ciências da Saúde) (1982 to September 2014) and Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library (Issue 8, 2014). The searches were
Results
The electronic searches yielded 208 potentially relevant studies that were selected for titles and abstracts reading. A flow chart demonstrating the process for selecting relevant articles is showed in Fig. 1. After examining the titles and abstracts, 156 articles were excluded (02 in Polish and 02 in German). Twenty-three articles did not deal with seasonality or differentiate attempted suicide and suicide. Only 29 studies satisfied all criteria and were extensively analyzed (Table 1).
As shown
Discussion
The current review included mostly retrospective cross-section studies published in the last four decades and investigating the seasonal pattern of suicide attempts. The majority (23/29) reported a higher peak in suicide attempts in spring or summer. Only three articles did not find seasonality in suicide attempts (Aydin et al., 2013, Nakamura et al., 1994, Saadat, 2005). However, the study of Saadat (2005) was restricted to evaluate self-inflicted injuries from burns and the sample size was
Conclusion
We described in this systematic review that seasonal variation is an important epidemiological observation also for suicide attempts. To our knowledge this is the first systematic review on this topic. An overall pattern was observed for a peak in spring, independent of sex, region and type of method used. This tendency for a higher incidence of suicide behavior in spring could be a consequence of the increasing photoperiod and light intensity in this season. However, further studies are
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