Long-Term Nightshift Work and Breast Cancer Risk: An Updated Systematic Review and Meta-Analysis with Special Attention to Menopausal Status and to Recent Nightshift Work

• Published in: Cancers 2021-11, Vol.13 (23), p.5952
• Main Authors: Schwarz, Christine, Pedraza-Flechas, Ana María, Pastor-Barriuso, Roberto, Lope, Virginia, de Larrea, Nerea Fernández, Jiménez-Moleón, José Juan, Pollán, Marina, Pérez-Gómez, Beatriz
• Format: Article
• Language: English
• Subjects: Age; Breast cancer; Circadian rhythm; Circadian rhythms; Female employees; Hormone replacement therapy; Menopause; Meta-analysis; Pacemakers; Post-menopause; Reviews; Systematic Review; Tumors; Womens health
• ISSN: 2072-6694; 2072-6694
• DOI: 10.3390/cancers13235952

This systematic review discusses long-term NSW and female BC risk, with special attention to differences between pre- and postmenopausal BC, to test the association with recent NSW. The review follows PRISMA guidelines (Prospero registry: CRD42018102515). We searched PubMed, Embase, and WOS for case–control, nested case–control, and cohort studies addressing long-term NSW (≥15 years) as risk exposure and female BC as outcome until 31 December 2020. Risk of bias was evaluated with the Newcastle–Ottawa scale. Eighteen studies were finally included (eight cohorts; five nested case–control; five case–control). We performed meta-analyses on long-term NSW and BC risk; overall and by menopausal status; a subanalysis on recent long-term NSW, based on studies involving predominantly women below retirement age; and a dose–response meta-analysis on NSW duration. The pooled estimate for long-term NSW and BC was 1.13 (95%CI = 1.01–1.27; 18 studies, I2 = 56.8%, p = 0.002). BC risk increased 4.7% per 10 years of NSW (95%CI = 0.94–1.09; 16 studies, I2 = 33.4%, p = 0.008). The pooled estimate for premenopausal BC was 1.27 (95%CI = 0.96–1.68; six studies, I2 = 32.0%, p = 0.196) and for postmenopausal BC 1.05 (95%CI = 0.90–1.24,I2 = 52.4%; seven studies, p = 0.050). For recent long-term exposure, the pooled estimate was 1.23 (95%CI = 1.06–1.42; 15 studies; I2 = 48.4%, p = 0.018). Our results indicate that long-term NSW increases the risk for BC and that menopausal status and time since exposure might be relevant.