Abstract Introduction Chronic stress from sleep deprivation, circadian disruption, and occupational demands among shift workers may increase cumulative wear-and-tear on the body, known as allostatic load (AL). Additionally, individuals with a high prevalence of Adverse Childhood Experiences (ACEs) exhibit heightened vulnerability to disease, and this risk may be particularly pronounced among shift workers with elevated ACE exposure. Mitochondrial DNA (mtDNA) is highly susceptibility to reactive oxygen species-induced damage and therefore has been described as a marker for poor health. Here, we investigate the relationship between stressful early-life events and immune cell mtDNA in shift workers. Methods 12 day-shift (DS) (aged 30-55; 5 females) and 12 night-shift (NS) workers (aged 27-52; 9 females) participated in this combined field/laboratory study. Participants completed their regular shift cycle, slept at home, and then reported to the laboratory as if beginning another shift. Participants completed a strictly controlled 24-hour constant routine with continuous wake, and blood collections via intravenous catheter every 6 hours. Real-time PCR was performed on sheared, genomic DNA extracted from peripheral blood mononuclear cells from each sample (n=4/participant) using primers targeting the mtDNA gene hMito3 (127bp amplicon size). Results were normalized to the nuclear DNA (nDNA) gene B2M1 (188bp amplicon size). The mtDNA to nDNA ratio reflects the mtDNA copy number (mtDNAcn), allowing for comparison of mtDNA across individuals. The ACE questionnaire was administered during a pre-study screening session. Results T-tests revealed no significant differences of mtDNAcn (t(22)=−0.39, p=0.70 or ACE scores (t(22)=−0.41, p=0.69) between NS and DS workers. Pearson’s correlation was used to compare the averaged mtDNAcp to the ACE scores of the NS and DS workers. ACE scores were positively correlated with mtDNAcn (r=0.66, p=0.02) in NS, but not DS workers (r=0.08, p=0.79). Conclusion This combined field/laboratory study revealed significant associations between mtDNAcn and exposure to ACEs. These findings suggest that mtDNA alterations may represent a cellular pathway through which early-life stressors manifest physiologically. This mechanistic link provides a foundation for future research exploring how stress contributes to an accelerated AL, particularly among night shift workers. Support (if any) BCS: Andy Hill CARE Fund SG: NIH award R01ES030113
Tolton et al. (Fri,) studied this question.