Breast cancer risk and lifetime leisure-time and occupational physical activity (Sweden).
OBJECTIVE
To clarify whether type and timing of physical activity affect postmenopausal breast cancer risk.


METHODS
In a population-based case-control study within the Swedish female population 50-74 years of age, 3347 women with invasive, postmenopausal breast cancer (84% of all eligible) and 3455 controls (82% of all selected) reported on past leisure-time physical activity. Record linkage to decennial census data (1960-1990) provided estimates of their occupational physical activity. Odds ratios with 95% confidence intervals were estimated by multivariate logistic regression.


RESULTS
After adjustment for potential confounders, women in sedentary occupations during their reproductive years (25-44 years of age) had a 50% higher risk for postmenopausal breast cancer, compared to those with the physically most demanding jobs. Only the most recent leisure-time physical activity was associated with a significant risk reduction. Women with the combination of sedentary jobs and lack of leisure-time exercise had a three-fold higher risk of breast cancer, compared to the physically most active both inside and outside the workplace.


CONCLUSIONS
Effects of occupational and leisure-time physical activity on breast cancer risk appear to have different latency times, and/or to be effect-modified by age or reproductive status. Although chance might explain our findings, it is advisable to consider type and timing of physical activity in future studies.
Moradi
T
T
Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden. Tahereh.Moradi@mep.ki.se
Nyrén
O
O
Zack
M
M
Magnusson
C
C
Persson
I
I
Adami
H O
HO
D000328:Adult; D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000517:prevention & control*; D016022:Case-Control Studies; D015444:Exercise; D005260:Female; D006801:Humans; D007899:Leisure Activities; D016015:Logistic Models; D008875:Middle Aged; D009790:Occupations; D016017:Odds Ratio; D017698:Postmenopause; D017584:Reproductive History; D012307:Risk Factors; D012923:Social Class; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology