Objectives There is limited research on the association between sedentary behaviour and breast cancer risk, particularly whether sedentary behaviour is differentially associated with premenopausal and postmenopausal breast cancer. We pooled data from 2 case–control studies from Australia and Canada to investigate this association.
Methods This pooled analysis included 1762 incident breast cancer cases and 2532 controls. Participants in both studies completed a lifetime occupational history and self-rated occupational physical activity level. A job-exposure matrix (JEM) was also applied to job titles to assess sedentary work. Logistic regression analyses (6 pooled and 12 study-specific) were conducted to estimate associations between both self-reported and JEM-assessed sedentary work and breast cancer risk among premenopausal and postmenopausal women.
Results No association was observed in the 6 pooled analyses, and 10 of the study-specific analyses also showed null results. 2 study-specific analyses provided inconsistent and contradictory results, with 1 showing statistically significant increased risk of breast cancer for self-reported sedentary work among premenopausal women cancer in the Canadian study, and the other a non-significant inverse association between JEM-assessed sedentary work and breast cancer risk among postmenopausal women in the Australian study.
Conclusions While a suggestion of increased risk was seen for premenopausal women in the Canadian study when using the self-reported measure, overall this pooled study does not provide evidence that sedentary work is associated with breast cancer risk.
- sedentary work
- breast cancer
- job-exposure matrix
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Contributors TB drafted the manuscript, prepared, harmonised and pooled the data, and conducted all statistical analyses and data interpretation. LF, LCK, JSH, DGL, SS, KJA and JJS contributed to data preparation, data analysis and/or interpretation of data, and provided feedback on the original and revised drafts of the manuscript. LF, JSH, KJA and JJS were also involved in the conception and design of the individual studies. All authors have read and approved of the submitted manuscript.
Funding The BCEES was supported by the Australian National Health and Medical Research Council (NHMRC Grant #572530) and by a grant from the Cancer Council Western Australia. The CBCS was supported by the Canadian Institutes of Health Research (Grant #69036). TB is supported by the Canadian Institutes of Health Research (Fellowship #300068), the Michael Smith Foundation for Health Research (Postdoctoral Fellowship #5553), Killam Trusts (Honorary Postdoctoral Research Fellowship), and the NHMRC (Early Career Fellowship #1072266). LF is supported by the NHMRC (Fellowship #37614900) and Cancer Council Western Australia (Fellowship).
Competing interests None declared.
Ethics approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The studies reported in this manuscript comply with the current laws of the country in which they were performed.
Provenance and peer review Not commissioned; externally peer reviewed.