Introduction New evidence suggests a physical activity (PA) health paradox, with positive health outcomes associated with high intensity leisure-time PA (LTPA), but negative health outcomes for those engaging in high intensity occupational PA (OPA). The aim of this study was to examine this paradox by systematically reviewing evidence on the association between high OPA and all-cause mortality.

Methods A systematic search of the literature was performed screening for eligible (peer-reviewed articles on prospective studies. Meta-analyses were performed assessing the association of high (compared to low) intensity OPA and all-cause mortality in males and females, estimating pooled hazard ratios (HR) with 95% confidence intervals (95% CI).

Results 2060 unique articles were screened of which 28 (from 24 studies with 2 88 264 participants) were included. We statistically pooled information from 19 studies, showing that males with high intensity OPA had a higher risk of early mortality than those with light intensity OPA (HR [95% CI]: 1.24 [1.03 1.49). Such an association was not observed for females (0.88 [0.75 1.03]).

Conclusion These findings support the PA health paradox, with levels of high intensity OPA being associated with ill-health (for males). An explanation for this finding may be the nature of OPA, involving sustained demanding tasks, causing chronically elevated blood pressure and heart rate responses. Males may be more prone than females because of gender differences in OPA, with males more likely to work in higher intensity occupations. Future research (preferably using objectively measured OPA) should further explore these potential mechanisms.