Physical Activity and Breast Cancer Risk in Postmenopausal Women:the SHAPE Study

Physical activity has been associated with a decreased risk for breast cancer. The biological mechanism(s) underlying the association between physical activity and breast cancer is not clear. Most prominent hypothesis is that physical activity may protect against breast cancer through reduced lifetime exposure to endogenous hormones. Another hypothesis is that physical activity prevents overweight and abdominal adiposity.

In this intervention study, 189 sedentary postmenopausal women who are aged 50-69 years are randomly allocated to an intervention or a control group. The intervention consists of an 1-year moderate-to-vigorous intensity aerobic and strength training exercise programme. Participants allocated to the control group are requested to retain their habitual exercise pattern. Primary study parameters measured at baseline, at four months and at 12 months are: serum concentrations of endogenous estrogens, endogenous androgens, sex hormone binding globulin and insulin. Other study parameters include: amount of total and abdominal fat, weight, BMI, body fat distribution, physical fitness, blood pressure and lifestyle factors.

This study will contribute to the body of evidence relating physical activity and breast cancer risk and will provide insight into possible mechanisms through which physical activity might be associated with reduced risk of breast cancer in postmenopausal women.

Inclusion criteria

• Women aged 50 -69 year
• > 12 months since last menses
• Non-smokers (at least 12 months)
• Sedentary
• Knowledge of the Dutch language
• Agreement to be randomly assigned to either the exercise intervention or control group
• Informed consent to participate in all screening and study activities

Exclusion criteria

• Use of hormone replacement or oral contraceptives in past 6 months
• Morbidly obese (BMI > 40)
• BMI < 22
• Currently on or planning to go on a strict diet
• Ever diagnosed with breast cancer
• Diagnosis of other types of cancer in the past 5 years
• Diabetes mellitus or other endocrine related diseases
• Disorders or diseases (locomotor, optical, neurological, mental) that might impede the participation in the exercise programme
• Alcohol or drug abuse
• Maintenance use of corticosteroids
• Use of beta blockers