Combined exposure to night work and noise in relation to hyperglycemia among long-term night workers: a nationwide population-based prospective cohort study.

Objectives: This study investigated the association between combined exposures and hyperglycemia incidence, as well as the dose-response relationship between the duration of night work and hyperglycemia among long-term night workers.

Methods: In this prospective cohort study, 12 716 night workers from the nationwide population were recruited. Hyperglycemia incidence was based on the one-year change in fasting blood glucose levels. Occupational noise exposure was defined as exposure to 8-hour time-weighted average sound levels of ≥85 decibels. Personal factors, including body mass index, and work-related factors, like monthly night work duration, were assessed. Multivariable logistic and linear regression models were used to explore the association.

Results: In the multivariate logistic analyses, each additional day of night work was associated with an increased risk of hyperglycemia [adjusted odds ratio 1.05, 95% confidence interval (CI) 1.02-1.07]. In the normal fasting glucose group, each additional day of night work was associated with a linear increase of +0.07% (95% CI +0.03% - +0.12%) in the change in fasting glucose levels, and noise exposure was associated with a linear increase of +1.34% (95% CI +0.55% - +2.12%) increase in fasting glucose levels. Furthermore, the population exposed to noise and working ≥10 days of night work had a significantly higher increase of fasting glucose levels (β +5.71%, 95% CI +4.48% - +6.95%), with significant interaction effects (P for interaction <0.01).

Conclusions: The possible dose-response relationship between duration of night work and changes in fasting glucose levels was found. The combined exposure to night work and noise posed a higher risk for hyperglycemia than exposure to night work alone.