Body mass index links night work intensity with higher low-grade systemic inflammation: results from a field study in humans.

Abstract

Objective: To examine effects of night work on low-grade systemic inflammation, measured as high-sensitivity C-reactive protein (hsCRP concentration), in hospital-employed women.

Methods: We analyzed baseline data from 929 women in the 1001 nights-cohort. Seven self-reported metrics captured night work history (never, past, current), night work duration (years) and recency (time since last night shift), current schedule (e.g., permanent night or 2- or 3-shift work), and intensity (number of weekly and consecutive night shifts, and night shifts in the past six days). We measured hsCRP concentration in blood. Associations between night work and log-transformed hsCRP concentration were estimated using generalized linear models: Model 1 adjusted for age and education; Model 2 additionally for body mass index (BMI), blood pressure, and health behaviors; Model 3 further for sleep duration and quality.

Results: Permanent night workers had a 49% higher hsCRP concentration than permanent day workers (estimate = 1.49; 95% CI: 1.07-2.10). In night shift workers, working ≥ 3 night shifts per week or ≥ 3 consecutive night shifts were associated with 36-53% higher hsCRP concentration compared with one weekly night shift or only single-night shifts. These associations were attenuated and became non-significant after adjustment for cardiometabolic risk factors. Additional analyses revealed that BMI largely attenuated the associations between night work intensity and hsCRP concentration. No associations were observed for other night work metrics.

Conclusion: Permanent night work and higher night work intensity were associated with higher hsCRP concentration, with differences largely explained by BMI. Reducing night work intensity and targeting modifiable factors related to BMI may help reduce low-grade systemic inflammation among night workers.