Assessment of potential risk factors for new onset disabling low back pain in Japanese workers: findings from the CUPID (cultural and psychosocial influences on disability) study.

BACKGROUND: Most studies of risk factors for new low back pain (LBP) have been conducted in Western populations, but because of cultural and environmental differences, the impact of causal factors may not be the same in other countries. We used longitudinal data from the Cultural and Psychosocial Influences on Disability (CUPID) study to assess risk factors for new onset of disabling LBP among Japanese workers.

METHODS: Data came from a 1-year prospective follow-up of nurses, office workers, sales/marketing personnel, and transportation workers, initially aged 20-59 years, who were employed in or near Tokyo. A baseline questionnaire included items on past history of LBP, personal characteristics, ergonomic work demands, and work-related psychosocial factors. Further information about LBP was collected at follow-up. Analysis was restricted to participants who had been free from LBP during the 12 months before baseline. Logistic regression was used to assess baseline risk factors for new onset of disabling LBP (i.e. LBP that had interfered with work) during the 12 months of follow-up.

RESULTS: Among 955 participants free from LBP during the 12 months before baseline, 58 (6.1%) reported a new episode of disabling LBP during the 12-month follow-up period. After mutual adjustment in a multivariate logistic regression analysis, which included the four factors that showed associations individually (p < 0.1) in analyses adjusted only for gender and age, the highest odds ratio (OR) was for past history of LBP (2.8, 95% [confidence interval {CI}]: 1.6-4.9), followed by working ≥60 h per week (1.8, 95% CI: 1.0-3.5) and lifting weights ≥25 kg by hand (1.6, 95% CI: 0.9-3.0). When past history of LBP was excluded from the model, ORs for the remaining risk factors were virtually unchanged.

CONCLUSIONS: Our findings suggest that among Japanese workers, as elsewhere, past history of LBP is a major risk factor for the development of new episodes of disabling back pain. They give limited support to the association with occupational lifting that has been observed in earlier research, both in Japan and in Western countries. In addition, they suggest a possible role of long working hours, which merits further investigation.