Relationship between Work Ability and Oxidative Stress

Introduction
Work ability is a complex concept determined by several factors, including age and physical and mental fitness. The Work Ability Index (WAI) consisting of 7 items is often used for estimation of work ability. Oxidative stress is detected before occurrence of clinically significant diseases as well as mental disorders. However, no study has investigated the association between work ability and markers of oxidative stress. The present study aimed to elucidate the association between work ability and oxidative stress using data from an intervention study with a lifestyle modification program.

Methods
A lifestyle modification program consisting of aerobic exercise and diet counseling was conducted for 12 weeks in the community. Data from 19 workers were obtained during the intervention. Work ability was assessed using the WAI, and markers of oxidative stress (plasma superoxide dismutase (SOD) activity and urinary 8-iso-prostaglandin F2α (PGF2α)) were determined before and after the intervention. The oxidative stress index was calculated as the ratio of PGF2α per SOD activity.

Results
The WAI score and PGF2α were negatively correlated (r = -0.40, p = 0.09). Among the WAI items, PGF2α showed significant negative correlation with psychological resources (r = -0.49, p = 0.03). The WAI score was unchanged by lifestyle modification (p = 0.97), whereas plasma SOD activity was significantly increased (p = 0.03). Among the changes by the intervention, the reductions in PGF2α and oxidative stress index showed significant correlation with the improvement in subjective work ability in relation to the demands of the job, which is a WAI item (r = -0.59, p = 0.01; r = -0.49, p = 0.03, respectively).

Discussion
Oxidative stress is associated with the work ability; this suggests that oxidative stress is a good indicator of work ability.