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ROTATING NIGHT SHIFT WORK AND RISK OF INVASIVE BREAST CANCER IN WOMEN OF THE NHS AND NHS II COHORTS: 24 YEARS OF FOLLOW-UP
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Sep 01 2017
Source: Am J Epidemiol. 186(5):532-540
[PDF-381.17 KB]
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Alternative Title:Am J Epidemiol
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Personal Author:
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Description:Objective
To evaluate associations between duration of rotating night shift work and invasive breast cancer in female nurses participating in two large longitudinal cohort studies.
Background
The International Agency for Research on Cancer (IARC) declared shift work that involves circadian disruption to be probably carcinogenic to humans (Group 2A) in 2007, citing earlier results from these cohorts. This analysis updates these findings with twice the follow-up time.
Methods
We conducted an analysis among women in the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHS II) with baseline (1988 for NHS: n=78,516 women ages 42-67; and 1989 for NHS II: n=114,559 women ages 24-42) as well as updated (NHS II only) lifetime rotating night shift work history. Follow-up for incident invasive breast cancer continued for 24 years (NHS: 1988–2012, NHS II: 1989–2013). We used multivariable-adjusted Cox proportional hazards models were used to calculate hazard ratios (HR) and 95% confidence intervals (CI).
Results
During 24 years of follow-up, we documented 9,541 invasive breast cancer cases (NHS: 5,971; NHS II: 3,570). Compared to women who never worked rotating night shifts, women in NHS with 30+ years of rotating night shift work at baseline did not experience an increased risk of breast cancer (HR30+ yrs vs 0 yrs=0.95, 95%CI 0.77-1.17; ptrend=0.63), However, in NHS II, breast cancer risk of women with 20+ years of rotating night shift work at baseline was significantly increased (HR20+ yrs vs 0 yrs=2.16, 95%CI 1.24-3.76; ptrend=0.23). Cumulative rotating night shift work (using updated exposure information) was associated with a marginally significant increased risk of breast cancer (NHS II only; HR20+ yrs vs 0 yrs=1.41, 95%CI 1.00-1.97; ptrend=0.73). The associations with breast cancer risk did not differ significantly by menopausal status at cancer diagnosis or estrogen and progesterone receptor status of tumors.
Conclusions
Results from our updated analyses of rotating night shift work and breast cancer risk are consistent with long-term rotating night shift work being associated with an increased risk of breast cancer. The addition of follow-up time in NHS, which occurred primarily post retirement, eliminated a previously observed increase in risk in these women and suggests that their heightened risk may wane with time.
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Pubmed ID:28541391
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Pubmed Central ID:PMC5856106
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