Jobs with high demands and strain increase a worker's risk of sick leave due to mental disorders, according to a recent study.

Swedish researchers found that workers with high job demands were at greater risk of sick leave due to mental disorders. Risk was also increased for workers with job strain, defined as high job demands with low control; and "iso-strain," defined as high demands and low control plus low levels of social support at work.

"Interventions to reduce sick leave due to mental disorders that focus on improving the psychosocial work environment, especially reducing high psychosocial job demands, may prove effective," Lisa Mather and coauthors wrote in the study.

For the five-year study, researchers used data from a Swedish national twin study involving nearly 12,000 workers to examine how rates of sick leave for mental health reasons are affected by psychosocial factors at work. They found that the rate of sick leave due to mental disorders was about eight percent. Three-fourths of workers with mental health sick leave were women.

They also found that workers with multiple unhealthy behaviors also had higher rates of mental health sick leave. Smoking was a significant risk factor, but alcohol use was not. High physical activity level was a protective factor.

The elevated risks associated with high job demand and job strain were unaffected by familial factors or health behaviors. Familial factors did seem to contribute to the risks associated with low job support, smoking, and unhealthy behaviors.

The study adds to previous evidence that psychosocial conditions at work affect rates of mental health sick leave -- and may suggest ways of reducing this risk.

The findings are detailed in the Journal of Occupational and Environmental Medicine.