The association between shift work and unhealthy weight: a cross-sectional analysis from the Nurses and Midwives' e-cohort Study.

OBJECTIVE To examine the association between shift work and unhealthy weight among female nurses and midwives. METHODS A cross-sectional study. Measurement outcomes included shift work, unhealthy weight (underweight: body mass index [BMI] < 18.5; overweight: BMI 25.0 to 29.9; obesity: BMI > 30.0), diet quality, physical-activity level, alcohol consumption, and smoking status. RESULTS Among the 2494 participants (1259 day and 1235 shift workers), only 1% of the participants were underweight, 31.8% were overweight, and 26.9% were obese. After adjusting the selected confounders, shift workers were 1.15 times more likely to be overweight/obese than day workers (P = 0.013, 95% confidence interval, 1.03 to 1.28; P = 0.02, 95% confidence interval, 1.02 to 1.30, respectively). CONCLUSIONS Shift work is associated with higher risk of being overweight/obese. Longitudinal studies are being undertaken to better understand the causal relationship between shift work and unhealthy weight.