The study also found that job burnout was the most significant risk factor for depression among the study participants.
Using specific questionnaires, Kirsi Ahola of the Finnish Institute of Occupational Health, Helsinki, and colleagues assessed burnout and job strain in a representative sample of 3,270 Finnish workers.
Workers with high scores for exhaustion and cynicism and low scores for professional effectiveness were considered to have burnout.
High job strain was defined as facing high work demands with little control over one's work. The workers also were assessed for symptoms of depression.
Twenty-eight percent of workers met the study definition of burnout, according to the researchers. Burnout was more common in older workers, those who were unmarried and those with manual occupations.
High alcohol use, physical inactivity, being overweight and having a physical or mental illness also increased the risk of burnout.
High job strain was present in 23 percent of workers, and was the most important risk factor for burnout. After adjustment for other factors, workers with high job strain were seven times more likely to be "burned out" than those with low job strain.
High job strain also was the strongest risk factor for depression, according to the researchers. Workers with high job strain were four times more likely to have depressive symptoms and 70 percent more likely to score in the "clinically depressed" range.
Study: Burnout May Be an Intermediate Step Between Job Strain and Depression
The relationship between job strain and burnout was little affected by adjustment for other factors, including indicators of physical and mental health, according to the researchers. In contrast, the association between job strain and depression all but disappeared after adjustment for burnout.
"This suggests that much of the association between job strain and depression is attributable to burnout," the researchers wrote.
Burnout and depression also were related to other categories of job strain: "active work," consisting of high job demands and high control; and "passive work," with low demands and low control.
The concept of job burnout - defined as "a state of exhaustion combined with doubts about the value of one's own work and competence" - is still debated among occupational health researchers. Previous studies have shown a close relationship between burnout, which is supposedly work-related; and depression, generally regarded as a more pervasive problem. The new study is the first to simultaneously assess all three factors in a large population representing the full range of occupations, the researchers assert.
Although the study can't prove any cause-and-effect relationship, the results suggest that burnout is an intermediate step in the relationship between job strain and depression. It also suggests that various types of job strain may contribute to burnout.