What mediates the inverse association between education and occupational disability from back pain?--A prospective cohort study from the Nord-Trøndelag health study in Norway

Low education is consistently associated with an increased risk of back pain disability, but the underlying mechanisms for this relationship are poorly understood. In a seven-year prospective observational study of 38,426 employed men and women between 25 and 59 years in Norway, we investigated to what extent occupational class, working conditions and individual lifestyle mediated the effect of formal education on disability pensioning from back pain. Each additional year of formal education was associated with decreased risk for disability pensioning from back pain for both men [age adjusted Hazard Ratio (HR) 0.77; (95% Confidence Interval, 0.72-0.82)] and women [HR 0.76(0.71-0.82)]. Adjustment for occupational class and factors related to working conditions (authority to plan own work, physically demanding work, concentration and attention and job satisfaction) and individual lifestyle (smoking, body mass index, physical exercise and alcohol consumption) reduced the effect of education by 39% [HR 0.86(0.79-0.93)] for men and by 21% [HR 0.81(0.73-0.89)] for women. Working conditions contributed most to the explanation for men, while occupational class, working conditions and life style factors contributed equally for women. Subgroup analyses indicate small differences between full-time and part-time employees, while some differences were found between subcategories of back diseases. The study indicates that there is a strong and unexplained effect of education on back pain disability pensioning, which is not mediated by occupational class, working conditions or individual lifestyle.