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Physical activity in the primary prevention of estrogen-related cancers: is it effective? |
Campbell K L, Harris S R |
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Authors' objectives To examine the influence of exercise, or physical activity in general, on the risk for oestrogen-related cancers.
Searching MEDLINE and CINAHL were searched from 1985 to August 1998 using the following terms: 'breast cancer', 'physical activity', 'exercise', 'estrogen-related cancers'. The search was restricted to publications in the English language. The reference lists from previously identified research articles were also used to locate additional references.
Study selection Study designs of evaluations included in the reviewProspective cohort, retrospective cohort, case-control, and 'record-linkage' studies were included.
Specific interventions included in the reviewExercise or physical activity, which could be recreational and/or occupational.
Participants included in the reviewWomen of all nationalities and ages. The participants included were premenopausal women, women with breast cancer, athletes, physical education teachers, and nurses.
Outcomes assessed in the reviewThe risk for breast cancer, endometrial cancer and ovarian cancer was assessed.
How were decisions on the relevance of primary studies made?The authors do not state how the papers were selected for the review, or how many of the reviewers performed the selection.
Assessment of study quality The authors do not state that they assessed quality.
Data extraction The authors do not state how the data were extracted for the review, or how many of the reviewers performed the data extraction. Data were extracted for the following categories: study identification; study design; participants; type of physical activity; and results.
Methods of synthesis How were the studies combined?A narrative synthesis was undertaken. The authors described the studies with reference to the levels of evidence (i.e. Level I to V) assigned according to Sackett's rules of evidence (see Other Publications of Related Interest).
How were differences between studies investigated?Within each section (breast cancer, endometrial cancer, and ovarian cancer), the studies were classified by the type of physical activity (i.e. recreational or leisure activity versus occupational activity).
Results of the review Overall, 27 studies with at least 306,083 participants were included in the review. Twenty-two studies with 271,740 participants examined breast cancer: 12 were case-control studies, 4 were prospective cohorts, 5 were retrospective cohorts, and 1 was a record-linkage study. Nine studies with 26,730 participants examined endometrial cancer (5 studies also examined breast and ovarian cancer): 5 were case-control studies, 3 were retrospective cohorts, and 1 was a record-linkage study. Five studies with 54,575 participants investigated ovarian cancer (4 studies also examined breast and endometrial cancers): 3 were retrospective cohorts, 1 was a prospective cohort and 1 was a record-linkage study.
Breast cancer.
Fifteen of the breast cancer studies showed a protective benefit of physical activity, 5 showed no association, and 2 reported a negative effect of physical activity.
Endometrial cancer.
A positive association between increasing levels of physical activity and decreasing endometrial cancer risk was demonstrated across the 9 studies; 7 of the 9 studies showed a protective effect. Ovarian cancer.
Two studies showed a protective effect, one showed a negative effect, and the remaining study showed no effect.
Authors' conclusions The available evidence, albeit limited to Level III studies, suggested that regular exercise may be an important tool in the prevention of oestrogen-dependent cancers.
CRD commentary Detailed inclusion and exclusion criteria were lacking. An adequate literature search was conducted, although it was restricted to English language publications. In addition, the authors did not state if they made any attempt to identify unpublished research. It is therefore possible that some studies may have been missed. Information was presented for each of the individual studies, although it was not detailed, i.e. age, specific types of physical activity, and quantitative outcome measures were not presented. In addition, there was no assessment of the overall quality of the individual studies. The authors did not state how many of the reviewers selected the studies and extracted the data. Without a detailed description of the study results, it is unclear whether the studies have been summarised appropriately. Also, two studies using the same participants have been considered separately in the text. The conclusions appear to follow from the results. However, as it is unclear whether the studies included in the review were of a good quality, and due to the limitations of the review, the conclusions should be treated with caution.
Implications of the review for practice and research Practice: The authors state that regular, moderate-intensity recreational exercise should be recommended to women of all ages.
Research: The authors state that future research should include large, long-term prospective studies (of at least 10 years) in which premenopausal women are randomly assigned to various levels of exercise intensities. In addition, future studies should collect data concerning the participants' race, ethnicity, socioeconomic status and sexual preference, in order to analyse the effects of exercise on preventing oestrogen-related cancers in women from diverse backgrounds.
Funding Health Canada (British Columbia Centre of Excellence for Women's Health); Canadian Breast Cancer Foundation.
Bibliographic details Campbell K L, Harris S R. Physical activity in the primary prevention of estrogen-related cancers: is it effective? Physiotherapy Canada 2000; 52(3): 198-207 Other publications of related interest Sackett DL. Rules of evidence and recommendations on the use of antithrombotic agents. Chest 1989;95:2S-4S.
Indexing Status Subject indexing assigned by CRD MeSH Breast Neoplasms /prevention & Endometrial Neoplasms /prevention & Exercise /therapeutic use; Ovarian Neoplasms /prevention & control; control; control AccessionNumber 12000005349 Date bibliographic record published 31/07/2002 Date abstract record published 31/07/2002 Record Status This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn. |
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