By David Liu, PHD

Tuesday Aug 28, 2012 (foodconsumer.org) -- A new study in Cancer Prevention Research suggests that overweight and obesity can increase invasive breast cancer risk in premenopausal women.

The study led by Reena Cecchini of  University of Pittsburgh Graduate School of Public Health and colleagues showed women who had obesity or overweight were at least 57 percent more likely to develop invasive breast cancer, compared to those who had a normal BMI.

High body mass index (BMI) or obesity and overweight has been linked with an elevated risk for breast cancer among postmenopausal women in previous studies. However, the relationship between BMI and breast cancer risk in premenopausal women is unclear,  according to the authors. 

The study was based on data from the Breast Cancer Prevention Trial involving 12,243 participants with 253 invasive breast cancer events identified and the Study of Tamoxifen and Raloxifene involving 19,488 participants with 557 events recorded. Both trials were conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP). In both trials, enrolled were women with high risk for breast cancer (Gail score = 1.66), but without breast cancer history.

Among premenopausal participants, those who had obesity or overweight had an increased risk of invasive breast cancer. Compared to those with a normal BMI, premenopausal overweight women were 59 percent more likely to have invasive breast cancer and premenopausal women with obesity were 70 percent more likely to have the disease. The associations were adjusted for other confounders.

The researchers concluded "higher levels of BMI were significantly associated with increased breast cancer risk in premenopausal women older than age 35, but not postmenopausal women."

In the U.S. one in eight women are expected to be diagnosed with breast cancer in their lifetime.  This disease in many cases is preventable by following a healthy lifestyle including a healthy diet.  Two important things to consider to lower the risk, avoiding medical radiation used in diagnostic tools and treatment and hormone replacement therapy, both are known to increase the risk.