Does age modify the association between physical work demands and deterioration of self-rated general health?

Objective Due to the growing proportion of older employees in the work force in several countries, the importance of age in the association between work and health is becoming increasingly relevant. Few studies have investigated whether age modifies the association of physical work demands with health. We hypothesized that the association of demanding body postures with deteriorated self-rated health (SRH) is stronger among older employees than among younger employees. Method We analyzed three 5-year cohorts in the Danish Work Environment Cohort Study comprising 8318 observations from 5204 employees (follow-up participation rate 83%) with good baseline SRH. Physical work demands were assessed as demanding body postures. Age was divided into tertiles; young (18-32 years), middle-aged (33-43 years) and old (44-59 among men and 44-54 years among women). Poor SRH ("fairly good", "poor", and "very poor") was measured with a single item. Log binomial regressions were stratified by gender. Effect modification (ie, interaction) was defined as deviation from additivity and examined by calculating the relative excess risk due to interaction (RERI). The reference group was employees aged 18-32 years with low physical exposure. Results When predicting deterioration of SRH, an interaction between demanding body postures and age was found among men [RERI: 0.75, 95% confidence interval (95% CI) 0.16-1.34, regarding the age group 44-59 years] and among women (RERI: 0.84, 95% CI 0.19-1.34, for the age group 33-43 years; and 1.17, 95% CI 0.42-1.93, for the age group 44-54 years). Conclusion The study findings suggest that demanding body postures have a stronger impact on health among older compared to younger employees.