Introduction Disruption of age-related processes seems to play a relevant role in health effects related to night shift (NS) work. We had observed a decrease between telomere length (a marker of aging) and number of years in NS in subjects employed in NS ≥12 years.

Objectives We now investigate the association between NS work and biological age (BA) estimated through an epigenetic signature based on methylation of five CpG sites in ELOVL2, C1orf132, TRIM59, KLF14 and FHL2 (Zbieć-Piekarska et al., 2017).

Methods Forty-six female nurses employed in NS for at least two years were matched by age (30–45 years) and length of service (≥1 year) with 51 female colleagues not working in NS. Each subject filled in a semi-structured questionnaire [including the Effort Reward Imbalance (ERI) index to assess job stress] and gave a blood sample. We applied linear regression models adjusted for BMI, ERI, and smoking habit and performed stratified analyses to investigate effect modifiers. We estimated age acceleration by regressing biological age on chronological age and taking the residuals.

Results Working in NS and number of years in NS were not associated with BA in the overall population. Overweight/obese subjects showed an increase in age acceleration per each year in NS [0.46 (0.05; 0.87), p = 0.030, p for interaction = 0.097] as well as subjects exposed to occupational stress (ERI >1) [0.58 (0.10; 1.06), p = 0.018, p for interaction = 0.056]. Interestingly, we observed a higher age acceleration [0.66 (0.03; 1.29), p = 0.041] when considering both categories combined, even if no formal interaction was apparent.

Conclusion Although hampered by the small sample size, our findings suggest a relationship between age acceleration and number of years in NS in hypersusceptible workers, i.e. overweight/obese or exposed to occupational stress.