Duration of shiftwork related to body mass index and waist to hip ratio

OBJECTIVE: An elevated cardiovascular disease risk for shiftworkers has frequently been reported, however, the mechanism is still unknown. Changes in eating habits, in physical activity or metabolic factors could be involved. In this study we assessed the relationship between body mass index (BMI) as a possible indicator of changed eating habits or metabolic involvement and duration of shiftwork. DESIGN: Data from an ongoing cohort study among 377 shiftworkers and non-shiftworking controls, all starting in a new job were used, Anthropometric measurements were carried out at the start of the assignment. Job history was obtained by a questionnaire. RESULTS: A positive relationship was observed between BMI and waist to hip ratio (WHR) and duration of shiftwork experience, with an adjustment for age. The linear regression coefficients, with additional adjustments for sex, smoking status, physical activity and educational level were 0.12 kg/m(2) per y in shiftwork for BMI (P < 0.05) and 0.0016 per y in shiftwork for WHR (P < 0.05). CONCLUSIONS: These results suggest a relationship between years worked in shifts with BMI and WHR for both males and females. Whether this might reflect an effect of changed dietary habits or a metabolic effect is not yet clear.