Night Shift Work, DNA Methylation and Telomere Length: An Investigation on Hospital Female Nurses

Abstract

Increased breast cancer risk has been reported in some night shift (NS) workers but underlying biological mechanisms are still unclear. We assessed the association between NS work and DNA methylation of tumor suppressor (TP53, CDKN2A, BRCA1, BRCA2) and estrogen receptor (ESR1, ESR2) genes, methylation of repetitive elements (LINE-1, Alu), and telomere length (TL). 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 underwent a semi-structured interview and gave a blood sample. We applied linear regression and spline models adjusted for age, BMI, smoking habit, oral contraceptive use, parity and marital status/age at marriage. Currently working in NS was associated with ESR1 hypomethylation (β: −1.85 (95%CI: −3.03; −0.67), p = 0.003). In current and former NS workers we observed TP53 (−0.93 (−1.73; −0.12), p = 0.03) and BRCA1 (−1.14 (−1.71; −0.58), p <0.001) hypomethylation. We found an increase between TL and number of years in NS in subjects employed in NS <12 years (0.06 (0.03; 0.09), p <0.001), while a decrease if employed in NS ≥12 years (−0.07 −0.10; −0.04), p <0.001). Our findings show NS-associated markers potentially involved in cellular aging, genomic instability, and cancer development.

Telomere Length as a Biomarker of Biological Aging in Shift Workers

“…An investigation carried out by Carugno et al [60] underlines a correlation between extended exposure to SW and molecular modifications that might be implicated in the process, for example, cellular aging. They found an increasing between telomere length and several years in SW in workers in SW < 12 years (0.06 (0.03; 0.09), p < 0.001), while a reduction if work was involved in SW ≥ 12 years (−0.07 −0.10; −0.04), p < 0.001), but this does not clarify the average number of nights made by workers.…”

“…To date, the information base on telomere length as a biomarker in occupational setting seems to be growing. Telomere shortening is correlated with SW and long duration of work [54][55][56][57][58][59][60].…”

“…Early evidence from studies in SW [54][55][56][57][58][59][60] points out that SW may have due effects on aging and telomere length, in particular with the intensity of SW.…”

“…Seven were ruled out after subsequent review of title and abstract, and six studies were disqualified after review of the manuscript. Finally, seven studies satisfied the inclusion criteria and were included in the systematic review [54][55][56][57][58][59][60]. A flow-chart depicting the choice of studies is revealed in Figure 1.…”

Relationship between Night Shifts and Risk of Breast Cancer among Nurses: A Systematic Review

“…Those who exceeded all the criteria were given a positive sign (+) and those who did not, a negative one (−), thus being excluded. The inclusion criteria list can be seen in Table 3 [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ].…”