Table 2.

Results of subgroup analyses and meta-regression analyses on the correlation between night shift work and the risk of breast cancer in women

Risk estimatesHeterogeneity
SubgroupNumber of studiesaWeight (%)OR (95% CI)PPI2Pinteraction
Geographic location0.472
Europe27 (22, 26–27, 32, 38–44, 47, 50–51, 57, 59–62, 67–68, 74, 77–78, 81)54.421.416 (1.246–1.610)0.0000.00077.4%
North America13 (29, 36, 45–46, 49, 55, 58, 64–65, 71, 82)251.236 (1.048–1.459)0.0120.00165.3%
Asia7 (30, 35, 37, 53–54, 72, 76)15.131.236 (0.865–1.767)0.2450.00088.3%
Australia2 (56, 70)5.451.040 (0.852–1.271)0.6980.8950.0%
Study design0.584
Cohort study14 (22, 26, 27, 29, 30, 32, 57, 65, 74, 76–77, 81, 82)32.321.193 (1.030–1.382)0.0190.00072.5%
Case–control24 (35–38, 40–41, 43–46, 49–51, 53, 55–56, 58, 64, 68, 70–71, 78)47.791.329 (1.189–1.486)0.0000.00063.1%
Nested case–control11 (39, 42, 47, 54, 59–62, 67, 72)19.891.555 (1.115–2.169)0.0090.00090.0%
Number of variables0.592
≤315 (32, 37, 39, 43, 45, 54, 56, 60–62, 65, 68, 72, 77)31.181.440 (1.139–1.820)0.0020.00089.1%
>334 (22, 26–27, 29–30, 35–36, 38, 40–42, 44, 46–47, 49–51, 53, 55, 57–59, 64, 67, 70–71, 74, 76, 78, 81, 82)68.821.273 (1.152–1.405)0.0000.00071.4%
Study score0.658
Low14 (32, 35, 37, 39, 43, 54, 60–62, 65, 68, 72, 77)30.371.434 (1.133–1.814)0.0030.00089.7%
High35 (22, 26–27, 29–30, 36, 38, 40–42, 44–47, 49–51, 53, 55–59, 64, 67, 70–71, 74, 76, 78, 81, 82)69.631.273 (1.152–1.407)0.0000.00071.3%
Exposure assessment0.077
Database10 (32, 35, 39, 60–62, 65, 68, 77)21.851.452 (1.211–1.741)0.0000.00167.2%
Questionnaire12 (22, 29, 36, 45, 47, 59, 70, 74, 76, 81, 82)21.421.380 (1.137–1.676)0.0010.00165.2%
Interview25 (26–27, 30, 37–38, 40–44, 46, 49–51, 53, 55–57, 64, 67, 71–72, 78)49.541.287 (1.126–1.471)0.0000.00068.6%
Other2 (54, 58)7.190.906 (0.596–1.378)0.6450.00097.6%
Occupation0.350
Nurses11 (29, 36, 38, 39, 42, 65, 67, 68, 82)21.021.577 (1.235–2.014)0.0000.00072.0%
Unclassified occupation30 (22, 26–27, 30, 32, 35, 37, 40–41, 43–46, 49–51, 53, 55–58, 64, 70–72, 74, 76, 78, 81)63.601.250 (1.130–1.383)0.0000.00073.3%
Flight attendants5 (59–62)7.981.454 (1.100–1.922)0.0090.16139.0%
Military women1 (47)1.132.100 (0.990–4.455)0.053
Textile workers1 (54)3.550.730 (0.655–0.814)0.000
Radio and telegraph operators1 (77)2.731.500 (1.112–2.023)0.008
  • aSome enrolled articles discussed more than one type of cancer separately, when calculating the number of studies; we took different cancers into consideration in one article.