TY - JOUR
T1 - Night-shift work and breast cancer - A systematic review and meta-analysis
AU - Ijaz, Sharea
AU - Verbeek, Jos
AU - Seidler, Andreas
AU - Lindbohm, Marja Liisa
AU - Ojajärvi, Anneli
AU - Orsini, Nicola
AU - Costa, Giovanni
AU - Neuvonen, Kaisa
PY - 2013
Y1 - 2013
N2 - Objective The aim of this review was to synthesize the evidence on the potential relationship between nightshift work and breast cancer. Methods We searched multiple databases for studies comparing women in shift work to those with no-shift work reporting incidence of breast cancer. We calculated incremental risk ratios (RR) per five years of night-shift work and per 300 night shift increases in exposure and combined these in a random effects dose-response meta-analysis. We assessed study quality in ten domains of bias. Results We identified 16 studies: 12 case-control and 4 cohort studies. There was a 9% risk increase per five years of night-shift work exposure in case-control studies [RR 1.09, 95% confidence interval (95% CI) 1.02-1.20; I2=37%, 9 studies], but not in cohort studies (RR 1.01, 95% CI 0.97-1.05; I2=53%, 3 studies). Het¬erogeneity was significant overall (I2=55%, 12 studies). Results for 300 night shifts were similar (RR 1.04, 95% CI 1.00-1.10; I2=58%, 8 studies). Sensitivity analysis using exposure transformations such as cubic splines, a fixed-effect model, or including only better quality studies did not change the results. None of the 16 studies had a low risk of bias, and 6 studies had a moderate risk. Conclusions Based on the low quality of exposure data and the difference in effect by study design, our find¬ings indicate insufficient evidence for a link between night-shift work and breast cancer. Objective prospective exposure measurement is needed in future studies.
AB - Objective The aim of this review was to synthesize the evidence on the potential relationship between nightshift work and breast cancer. Methods We searched multiple databases for studies comparing women in shift work to those with no-shift work reporting incidence of breast cancer. We calculated incremental risk ratios (RR) per five years of night-shift work and per 300 night shift increases in exposure and combined these in a random effects dose-response meta-analysis. We assessed study quality in ten domains of bias. Results We identified 16 studies: 12 case-control and 4 cohort studies. There was a 9% risk increase per five years of night-shift work exposure in case-control studies [RR 1.09, 95% confidence interval (95% CI) 1.02-1.20; I2=37%, 9 studies], but not in cohort studies (RR 1.01, 95% CI 0.97-1.05; I2=53%, 3 studies). Het¬erogeneity was significant overall (I2=55%, 12 studies). Results for 300 night shifts were similar (RR 1.04, 95% CI 1.00-1.10; I2=58%, 8 studies). Sensitivity analysis using exposure transformations such as cubic splines, a fixed-effect model, or including only better quality studies did not change the results. None of the 16 studies had a low risk of bias, and 6 studies had a moderate risk. Conclusions Based on the low quality of exposure data and the difference in effect by study design, our find¬ings indicate insufficient evidence for a link between night-shift work and breast cancer. Objective prospective exposure measurement is needed in future studies.
KW - Dose-response
KW - Evidence synthesis
KW - Shift work
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U2 - 10.5271/sjweh.3371
DO - 10.5271/sjweh.3371
M3 - Article
C2 - 23804277
AN - SCOPUS:84883377320
VL - 39
SP - 431
EP - 447
JO - Scandinavian Journal of Work, Environment and Health
JF - Scandinavian Journal of Work, Environment and Health
SN - 0355-3140
IS - 5
ER -