Abstract
BACKGROUND: Night shift work disrupts circadian rhythms and has been associated with various health disorders, particularly in older adults. Biological age indicators, such as telomere length (TL) and DNA methylation (DNAm) age, offer effective tools to assess early ageing-related changes Linked to occupational exposures. This study aims to investigate the association between night shift work and biological ageing markers among workers aged over 50 years. METHODS: Participants were classified as current, former, or never night shift workers. TL was measured via quantitative PCR, and DNAm age was estimated based on methylation at five CpG sites. Age acceleration (AA) was calculated as the residual from regressing DNAm age on chronological age. Associations between shift work and ageing markers were evaluated using univariate and multivariate analyses. RESULTS: Out of 330 workers invited, a total of 262 (response rate 79.6%) were recruited, predominantly male (87%) with a mean age of 54.5 ± 3.1 years. Current night shift workers exhibited significantly shorter telomeres compared to non-current shift workers (adjusted β = -0.07, p = 0.03). Among former shift workers, longer cumulative exposure was associated with reduced TL (β = -0.01, p = 0.004). Additionally, TL increased and AA decreased with each year since night shift cessation (β = 0.01, p=0.001 and β = -0.08, p=0.05, respectively). CONCLUSIONS: Prolonged night shift work is associated with telomere shortening, suggesting increased cellular ageing, partially reversible after night-shift cessation. DNAm age appears less sensitive to recent or cumulative shift work exposure.