Association between daily environmental temperature and suicide mortality in Korea (2001–2005)
Introduction
The mortality rates associated with suicide in Korea (Republic of) have sharply increased in recent years and are higher than those of other member nations of the Organization for Economic Cooperation and Development (OECD) (Kim, 2009, Kim et al., 2010). In 2007, suicide was the fourth leading cause of death among Koreans by Korea National Statistical Office (KNSO).
Although the internal and external characteristics of individuals such as mental and physical health, personal and family experiences, and educational and community were known as factors associated with suicide (Qin et al., 2003, Kim et al., 2006, Osborn et al., 2008, Kim et al., 2010), the weather condition, especially temperature, has been considered one of the risk factors. Partonen et al., 2004, Page et al., 2007 have reported that the suicide rate is much higher in the summer season. In addition, some studies have also shown a seasonality to suicide, and temperature has been identified as an important factor (Preti and Miotto, 1998, Preti, 2000, Qi et al., 2009). However, the debate whether the temperature can be a risk factor has remained understudied and continued (Ajdacic-Gross et al., 2007, Ajdacic-Gross et al., 2010).
To prove the hypothesis that the temperature effect may exist as a risk factor of suicide, studies with respect to the association between the temperature and suicide have been conducted mainly in Western countries (Partonen et al., 2004, Ajdacic-Gross et al., 2007, Page et al., 2007, Reutfors et al., 2009). In Asia, there have been few studies to examine the association between suicide and temperature except the studies in Taiwan (Lee et al., 2006, Tsai, 2010). The climate of Korea, located in the south of the Korean Peninsula (latitude 37°00′N and longitude 127°30′E) on the eastern Asia northern hemisphere is distinctly seasonal, i.e., temperature and relative humidity are high in summer, and winters are cold and dry, promoting an increased interest in the association between temperature and suicide.
Meanwhile, several studies demonstrated the different effects of temperature according to gender and age (Preti et al., 2007, Christodoulou et al., 2009). Preti (2000) found different seasonal trends in suicide between males and females. In addition, Kim and Joh (2006) suggested that the association between mortality and temperature may be more prevalent among elderly people with low incomes than among the general low-income population. These studies indicate that the association between temperature and suicide may differ according to gender and age.
Suicide rates and weather conditions vary across areas and regions of the world, and the association between temperature and suicide may depend on the applied modelling method and adjusted factors related weather variables (Deisenhammer, 2003, Ajdacic-Gross et al., 2010). Time-series regression approach applying generalized additive model (GAM) has been typically used in many studies for the association between temperature and mortality or air pollution and mortality (Schwartz, 1999, Curriero et al., 2002, O'Neill et al., 2003, Hu et al., 2008, Ren et al., 2008, Ha et al., 2009). This statistical model can control unmeasured time-varying potential confounders by using a smooth function of time. Many studies concerning the association between temperature and suicide have not applied the time-series regression approach using daily set (Preti and Miotto, 1998, Marion et al., 1999, Qi et al., 2009, Reutfors et al., 2009), although this methodology is more appropriate for examining the association between these two variables (Deisenhammer, 2003, Page et al., 2007, Ajdacic-Gross et al., 2010).
Therefore, the present study had two objectives: to examine the association between temperature and suicide, and to investigate whether the association differs with gender, age, or level of education.
Section snippets
Mortality data
The data on daily mortality counts associated with suicide among Koreans were derived from the Korea National Statistical Office (KNSO) for the period from 1 January 2001 through 31 December 2005. The X60–X84 codes from the International Classification of Diseases-10 (ICD-10), which include intentional self-poisoning and self-harm, were used for the analysis. The Y87.0, sequelae of intentional self-harm, were excluded from this analysis, because the association between immediate suicide and
Results
The annual suicide counts and suicide rates by gender, age, and education level are given in Table 1. The total number of suicides from 2001 to 2005 was 49,451, and the average number of suicides per year during the same period was 9890. Moreover, the yearly average suicide rate calculated from the population projection in 2003 was 20.9 per 100,000. The Korean suicide rate increased steadily from 2001 (count 6836; rate 14.6 per 100,000) to 2005 (count 11,989; rate 25.0 per 100,000) regardless
Discussion
This study aimed to examine the association between temperature and suicide and to investigate whether the association differed according to gender, age, or education level. Time-series regression analysis of suicide among the populations of Korea from 2001 to 2005 shows increases in all groups of suicide, such as gender, age, and level of education, with temperature levels on lag 0 day. However, the association between two issues was different by gender, age, and level of education, and the
Acknowledgement
This study was supported by the Ministry of Environment, Republic of Korea (Eco-Technopia 21 Project #091-071-057 and Graduate school program specialized on climate change).
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