Environment and Breast Cancer: Science Review
About
Occupational physical activity and risk for breast cancer in a nationwide cohort study in Sweden
Moradi, T.,, Adami, H.O.,, Bergstrom, R.,, Gridley, G.,, Wolk, A.,, Gerhardsson, M.,, Dosemeci, M.,, Nyren, O. Cancer Causes and Control. 1999. 10, 423-430.
Topic area
Physical Activity
Physical Activity
Study design
Prospective cohort (3 partly overlapping cohorts)
Prospective cohort (3 partly overlapping cohorts)
Funding agency
NCI NIEHS
NCI NIEHS
Study Participants
Number of Cases
20,419 (1960 cohort), 22,840 (1970 cohort), 8261 (both 1960 and 1970 cohorts), (invasive only)
20,419 (1960 cohort), 22,840 (1970 cohort), 8261 (both 1960 and 1970 cohorts), (invasive only)
Menopausal Status
Post menopausal
The menopausal status of women included in this study is listed here.
Pre menopausalPost menopausal
Number in Cohort
Cohort: 704,904 (1960), 982,270 (1970), 253,336 (both 1960 and 1970)
Cohort: 704,904 (1960), 982,270 (1970), 253,336 (both 1960 and 1970)
Cohort participation rate
Retention/participation exceeded 70% for exposed a
Retention/participation exceeded 70% for exposed a
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: Residents of Sweden; registered as employed
Ex: women who did not reply to nationwide census questionnaire which is required by law (1%)
Comment about participation selection
Strengths: Large cohort; large number of cases; high participation rate; obtained cases through the Swedish Cancer Registry which records 98% of all diagnosed cancers in Sweden; lengthy follow-up of 19 years; analyzed breast cancer risk by occupational physical activity stratified by age at follow-up; utilized a population based cohort Limitations: cohorts overlapped; obtained information through mailed questionnaires; did not stratify results by menopausal status; obtained physical activity levels from classified job titles instead of using self reported data; did not record occupational physical activity during the 19 year follow-up; did not record leisure time physical activity; did not confound for many important factors such as age of first child and parity
Strengths: Large cohort; large number of cases; high participation rate; obtained cases through the Swedish Cancer Registry which records 98% of all diagnosed cancers in Sweden; lengthy follow-up of 19 years; analyzed breast cancer risk by occupational physical activity stratified by age at follow-up; utilized a population based cohort Limitations: cohorts overlapped; obtained information through mailed questionnaires; did not stratify results by menopausal status; obtained physical activity levels from classified job titles instead of using self reported data; did not record occupational physical activity during the 19 year follow-up; did not record leisure time physical activity; did not confound for many important factors such as age of first child and parity
Exposure Investigated
Exposures investigated
Physical activity
Physical activity
How exposure was measured
Questionnaire, self-administered
Questionnaire, self-administered
Exposure assessment comment
Obtained physical activity levels from classified job titles instead of using self reported data
Obtained physical activity levels from classified job titles instead of using self reported data
Statistical Analysis
Breast cancer outcome investigated
Primary breast cancer
Primary breast cancer
Ethnic groups with separate analysis
If this study provided a separate analysis by ethnic or racial group, the groups are listed here.
No
Confounders considered
Other breast cancer risk factors, such as family history, age at first birth, and hormone replacement therapy use, that were taken into account in the study.
Adequately controlled, Confounders: age, calendar year of follow-up, place of residence, socio-economic status
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
No
Description of major analysis
Effect modifiers: age at follow-up Follow-up: 19 years
Effect modifiers: age at follow-up Follow-up: 19 years
Strength of associations reported
Increased association between breast cancer risk and women with a sedentary occupation vs women with a high/very high level of physical activity in their occupation, (1970 cohort) RR=1.3(1.3-1.4)
Increased association between breast cancer risk in women whose age at follow-up was 50-59 and women with a sedentary occupation vs women with a high/very high level of physical activity in their occupation, (women in both the 1960 and 1970 cohort) RR=1.5(1.3-1.7)
Increased association between breast cancer risk and women with a sedentary occupation vs women with a high/very high level of physical activity in their occupation, (1970 cohort) RR=1.3(1.3-1.4)
Increased association between breast cancer risk in women whose age at follow-up was 50-59 and women with a sedentary occupation vs women with a high/very high level of physical activity in their occupation, (women in both the 1960 and 1970 cohort) RR=1.5(1.3-1.7)
Results Comments
The protective effect of occupational physical activity is likely to be strongest among postmenopausal women who have been physically active for most of their lives
The protective effect of occupational physical activity is likely to be strongest among postmenopausal women who have been physically active for most of their lives