Suicide and occupation: further supportive evidence for their relevance Mariko Nishimura a , Takeshi Terao a, * , Shuji Soeda a , Jun Nakamura a , Noboru Iwata b , Kaoru Sakamoto c a Department of Psychiatry, University of Occupational and Environmental Health School of Medicine, Yahatanishi-ku, Kitakyushu 807-8555, Japan b Division of Health Science, University of East Asia, Shimonoseki, Japan c Department of Psychiatry, Tokyo Women’s Medical University, Tokyo, Japan Accepted 17 September 2003 Abstract In recent years, the relationship between occupation and suicide has been extensively investigated, but few definite conclusions regarding the nature of the relationship have been established. In the present study, this relationship was investigated by examining Japanese governmental statistics. First, correlations of suicide rate relative to industry categories were examined individually for primary industry (farmers, fishermen, and forest workers), secondary industry (construction workers, manufacture works, and miners), and tertiary industry (indoor workers) for all of the 47 prefectures of Japan. Second, in the industries that showed a significant correlation with suicide rate, the relationship to other factors was adjusted using possibly confounding factors. As a result, suicide rate was positively correlated with primary industry percentage, but not with secondary or tertiary industry percentages. Multiple regression analysis showed that suicide rate was positively associated with primary industry percentage with significant tendency while it was significantly and negatively associated with annual total sunshine. Limitations are that individual suicide rates according to occupational types were not available and direct correlations with the above variables could not be investigated. The present findings suggest a possibility that occupational factors associated with primary industry may be relevant to suicide, and that, additionally, annual total sunshine may affect suicide independently. Since workers with primary industry are likely to be exposed to sunshine than other workers, they may tend to be more affected by the decrease of annual total sunshine. D 2003 Elsevier Inc. All rights reserved. Keywords: Farmers; Fishermen; Forest workers; Primary industry; Suicide; Sunshine 1. Introduction Over recent years, there have been a number of investigations examining the relationship between occupa- tion and suicide both in terms of suicide rates within various occupations, and with regard to the job-related factors that influence suicide. One example is that of farmers in England and Wales who have a high rate of suicide compared to other occupations (Hawton et al., 1998; Malmberg et al., 1999). Also in Japan, workers of primary industry occupation had the highest rate of suicide (41.4 per 100,000 population in 1995) than any other occupation. Koskinen et al. (2002) showed that farmers were signif- icantly older at the time of suicide than construction or indoor workers and used more violent methods than the other occupational groups. Furthermore, suicide in farmers peaked significantly in the spring, whereas indoor workers had a significant peak of suicides in the summer (Koskinen et al., 2002). In addition, Malmberg et al. (1999) indicated that farmers are likely to be exposed to financial problems, although it does not mean that farmers are more likely to be exposed to financial problems than other occupational groups. Thus, rates of suicide may be influenced by occu- pational, environmental, and economic factors and are expected to differ from country to country. With regard to the relationship of season and suicide, Petridou et al. (2002) found a remarkably consistent pattern of seasonality with peak incidence of suicide around June in the northern hemisphere and December in the southern hemisphere, suggesting that sunshine may have a triggering effect on suicide (i.e., more sunshine, increased suicide). However, while previous studies, including those mentioned above, investigated monthly or seasonal changes of sun- 0278-5846/$ – see front matter D 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.pnpbp.2003.09.023 * Corresponding author. Tel.: +81-93-691-7253; fax: +81-93-692- 4894. E-mail address: t-terao@med.uoeh-u.ac.jp (T. Terao). www.elsevier.com/locate/pnpbp Progress in Neuro-Psychopharmacology & Biological Psychiatry 28 (2004) 83 – 87