The purpose of this study was to assess whether workplace bullying mediates between job strain, evaluated by the job demand-control model, and symptoms of depression and sleep disturbance. Methods: The subjects in this cross-sectional study were recruited from all the workers (N=2,634) at 50 organizations in Japan. Due to missing data, the numbers of subjects included in the analyses varied from 1,646 to 2,062 (response rates varied from 62.5% to 78.2%). Job strain and workplace social support, workplace bullying, depression, and sleep disturbance were assessed using the Japanese versions of the Job C o n t e n t Q u e s t i o n n a i r e , t h e N e g a t i v e A c t s Questionnaire, the Center for Epidemiologic Studies Depression Scale, and the Pittsburgh Sleep Quality Index, respectively. Mediation analysis followed the approach outlined by Baron and Kenny. We quantitatively estimated the mediation effects and tested their significance after adjustment for various combinations of demographic variables and workplace social support. Results: Total effects of job strain index on depression or sleep disturbance were all positive and significant (p<0.05) in both genders. Mediation effects of workplace bullying were also all positive and significant (p<0.05) in both genders. Even after adjustment for workplace social support, the mediation effects were decreased, especially in women, but remained significant (p<0.05). Conclusions: Workplace bullying seems to play important roles in the relationships of job strain with depression or sleep disturbance in both genders. (J Occup Health 2010; 52: 367-374)

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