As shown in Table 1, the number of articles identified in the review process was not evenly distributed among the major potential risk factors. The literature search identified most abstracts for physical exertion and psychosocial factors. However, after reviewing for inclusion criteria, relevance and quality, there were 22 studies concerning exposure to psychosocial factors at work but only two concerning chemical and biological factors that remained for further analysis.
The majority of the studies that fulfilled our inclusion, relevance, and quality criteria applied a prospective cohort design with at least one year follow-up time (>5 y: eight studies, 1–4 y: eight studies and