The effect of physical activity on breast cancer risk: a cohort study of 30,548 women.
BACKGROUND
In epidemiological studies abundant physical activity has been related to decreased breast cancer risk, though the results have been inconsistent. The purpose of this paper was to study the association of physical activity at leisure and commuting to work and incidence of breast cancer.


METHODS
The study cohort consisted of 30,548 female participants of the Finnish adult health behaviour survey, based on annual random samples of Finns aged 15-64, collected in 1978-1993. By the end of 1995, 332 breast cancer cases had been diagnosed in the cohort. Relative risks of breast cancer were adjusted for age at survey, body mass index (BMI), education, length of follow-up, parity and age at first birth using Poisson regression models.


RESULTS
Compared to women exercising less than once a week, the adjusted relative risk of breast cancer for women exercising once a week was 0.80 (95% confidence interval (CI): 0.58-1.10), for women exercising 2-3 times per week 0.92 (95% CI: 0.78-1.22) and for women exercising daily 1.01 (95% CI: 0.72-1.42). Women who reported commuting, walking or bicycling to work 30 min or more daily had slightly lower adjusted risk of breast cancer (RR: 0.87, 95% CI: 0.62-1.24) than women working at home, being unemployed or driving a car to working place.


CONCLUSIONS
Although a small protective effect of regular physical activity for breast cancer incidence was found in physical activity when commuting to work, the role of the physical activity in breast cancer prevention is still an open question.
Luoto
R
R
National Public Health Institute, Department of Epidemiology and Health Promotion, Helsinki and Tampere School of Public Health, University of Tampere, Finland. riitta.luoto@uta.fi
Latikka
P
P
Pukkala
E
E
Hakulinen
T
T
Vihko
V
V
D000293:Adolescent; D000328:Adult; D000368:Aged; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000517:prevention & control; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D015444:Exercise; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D015438:Health Behavior; D006801:Humans; D007899:Leisure Activities; D008875:Middle Aged; D010298:Parity; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014937:Work