Mechanisms of breast cancer risk in shift workers: association of telomere shortening with the duration and intensity of night work

Abstract

Occupational factors such as shiftwork and especially night work that involves disruption of the circadian rhythm may contribute to increased breast cancer risk. Circadian disruption may also affect telomere length (TL). While short TL generally is associated with increased cancer risk, its association with breast cancer risk is inconclusive. We suggest that working schedules might be an important factor in assessment of effects of TL on breast cancer risk. Moreover, telomere shortening might be a potential mechanism for night work‐related breast cancer. In this study, effects of shift work on TL and its association with breast cancer risk were investigated in a nested breast cancer case–control study of Norwegian nurses. TL was assessed by qPCR in DNA from 563 breast cancer patients and 619 controls. Here, we demonstrate that TL is affected by intensive night work schedules, as work with six consecutive night for a period of more than 5 years was associated with decreased telomere lengths (−3.18, 95% CI: −6.46 to −0.58, P = 0.016). Furthermore, telomere shortening is associated with increased breast cancer risk in workers with long periods of consecutive night shifts. Thus, nurses with longer telomere lengths had a lower risk for breast cancer if they had worked more than four (OR: 0.37, 95% CI: 0.16–0.79, P = 0.014) or five (OR: 0.31, 95% CI: 0.10–0.83, P = 0.029) consecutive night shifts for a period of 5 years or more. These data suggest that telomere shortening is associated with the duration and intensity of night work and may be a contributing factor for breast cancer risk among female shift workers.

Telomere Length as a Biomarker of Biological Aging in Shift Workers

“…This could be due to the influence of circadian rhythms on telomerase activity [55]; inflammation activity has been proven by Pavanello et al in two investigations [56,59]. Another evidence was done by Samulin Erdem and colleagues [57] that observed the telomere shortening correlated with the duration and intensity of SW and may be a contributing factor for breast cancer risk among the female workforce.…”

“…Telomere length was assessed from 563 breast cancer of shift workers and 619 controls. Erdem et al [57] demonstrate that telomere length is affected by intensive SW, as work with six successive nights for more than 5 years was correlated with decreased telomere lengths (−3.18, 95% CI: −6.46 to −0.58, p = 0.016). Telomere shortening is also correlated with a rise in breast cancer risk in workers with long periods of successive night shifts.…”

“…In a nested case-control study carried out in Norwegian nurses, telomere shortening is correlated with the interval and strength of night work and may be a co-factor for breast cancer risk between female shift workers [57]. Telomere length was assessed from 563 breast cancer of shift workers and 619 controls.…”

“…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].…”

“…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.…”