Obesity, Sedentary Lifestyle May Increase Risk of Breast Cancer

MedicalResearch.com: Interview Invitation
Dr. Wenji Guo
University of Oxford

Medical Research: What is the background for this study?

Response: Previous studies report increased risk for breast cancer in postmenopausal women who have a higher Body Mass Index (BMI) – a measure of body fat based on height and weight. However, BMI is unable to distinguish between excess weight due to fat rather than muscle. More direct measures of fatness, such as body fat percentage, may be better indicators of disease risk. And although probable evidence for the relationship between physical activity and breast cancer now exists, questions still remain over the role of vigorous compared to lower intensity physical activity.

Medical Research: What are the main findings?

Response: We investigated the associations between body fat percentage, total and vigorous physical activity, and breast cancer risk in 126,000 postmenopausal women who participated in UK Biobank. Women were aged 40-70 at the start of the study, with follow-up from 2006 through 2011. We observed 1,005 cases of invasive breast cancer during an average 2.9 years of follow-up.

We adjusted for age, geographical region, socio-economic status (based on Townsend deprivation index), family history of breast cancer, previous hormone replacement therapy use, height, parity, age at first birth, smoking, age at menarche, age at menopause, and alcohol intake frequency.

Compared with women in the lowest quartile of body fat percentage, those in the highest quartile had a 55% increased risk for breast cancer [95% confidence interval (CI) 1.33-1.82; p for trend <0.001]. Women who reported the most vigorous physical activity had a 21% lower risk for breast cancer compared to the least active women (95% CI 0.67-0.93; p for trend 0.006). Women who reported the most total physical activity had a non-statistically significant lower breast cancer risk (relative risk 0.88, 95% CI 0.74-1.05, p for trend 0.205).

Even after adjusting for body fat percentage, being physically active still seemed to help lower breast cancer risk suggesting that there may be benefits of exercise beyond its role in helping to maintain a healthy weight.

Medical Research: What should clinicians and patients take away from your report?

Response: Our findings suggest that maintaining a healthy weight and level of body fat is beneficial for reducing postmenopausal breast cancer risk. Our data also suggest a potential protective role of vigorous physical activity on postmenopausal breast cancer risk. The association between total physical activity and breast cancer risk was not statistically significant, although measurement error may have been involved.

Medical Research: What recommendations do you have for future research as a result of this study?

Response: Future research should incorporate more objective measures of physical activity, such as accelerometer data, although they too come with their own set of limitations. Our next steps will be to study associations between body size, physical activity, and breast cancer risk by breast cancer hormone receptor status.

2014 NCRI Cancer Conference abstract:
Body fat percentage, physical activity and breast cancer risk in 126,000 postmenopausal women in UK Biobank