Occupational physical activity and breast cancer risk in the upper Cape Cod cancer incidence study.
BACKGROUND
In several epidemiological studies, breast cancer risk has been reduced among women who reported high levels of occupational or leisure-time physical activity. We used data from a population-based case control study to evaluate the effect of occupational physical activity on breast cancer risk.


METHODS
Two hundred-thirty three incident cases of breast cancer and 670 controls or their next of kin were interviewed for information on breast cancer risk factors and a complete job history. Physical activity level of jobs were classified using a Department of Labor rating scheme. We calculated adjusted odds ratios for light and medium/heavy activity jobs compared to sedentary jobs.


RESULTS
Odds ratios for women who held medium/heavy jobs for less than 10 years and more than ten years were, respectively, 0.7 (95% CI = 0.4,1.3) and 1.7 (95% CI = 0.9,3.3).


CONCLUSIONS
In these data there was no evidence that holding a job of medium/heavy activity reduced breast cancer risk. The study was limited by misclassification inherent in the occupational exposure scheme and by the lack of information on leisure time physical activity. The modest risk increase for subjects holding a medium/heavy job for at least 10 years probably represents either confounding or random variation.
Department of Epidemiology and Biostatistics, Boston University School of Public Health, Boston, Massachusetts 02442, USA.
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Coogan
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Aschengrau
D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000453:epidemiology*; D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D015994:Incidence; D007899:Leisure Activities; D008404:Massachusetts / Q000453:epidemiology; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D016273:Occupational Exposure; D016272:Occupational Health; D016017:Odds Ratio; D011159:Population Surveillance; D012307:Risk Factors; D013997:Time Factors