Overweight/obesity is a significant risk factor for breast cancer.1 The American Institute for Cancer Research estimates that 17% of breast cancers (this equates to 33,000 new cases per year) are due to excess weight alone, and women who are obese when diagnosed are more likely to die from breast cancer after diagnosis.2
A study of 72,000 postmenopausal women presented at the 2010 American Association for Cancer Research annual meeting took into account body mass index (BMI) at age 20 and at their current age (55-74), and compared breast cancer risk between those who gained weight and those who did not. They found that a 5 point increase in BMI during these years doubled the likelihood of postmenopausal breast cancer compared to women whose BMI remained stable.3
Although excess weight has been consistently associated with breast cancer risk, the scientists undertook this study because previous studies investigating BMI or body weight during early adulthood were not conclusive. Rather than look simply at BMI at age 20, they looked at the change in BMI over time. Their results clearly indicate that weight gain puts women at risk for breast cancer, and confirms the importance of maintaining a healthy weight for cancer protection.
How much weight gain is risky?
Weight gain of 30 lbs. in a 5’4” woman would produce a 5 point increase. This may seem like a large amount of weight, but over thirty years, it would be a barely noticeable amount – a steady weight gain of 1 pound per year. This study suggests that even 1 pound per year is a dangerous amount of weight gain. And it turns out that this dangerous amount of weight gain is quite common - 60% of the women in the study had increased their BMI by at least 5 points since age 20.4 This tells us that most American women likely do gain this much weight during adulthood, doubling their risk of breast cancer.
Read more about breast cancer prevention.
1. Cleary MP, Grossmann ME. Minireview: Obesity and breast cancer: the estrogen connection. Endocrinology. 2009 Jun;150(6):2537-42.
2. Abrahamson PE, Gammon MD, Lund MJ, et al. General and abdominal obesity and survival among young women with breast cancer. Cancer Epidemiol Biomarkers Prev. 2006 Oct;15(10):1871-7.
3. Sue LY, Genkinger JM, Schairer C, Ziegler RG. Body mass index (BMI), change in BMI, and postmenopausal breast cancer risk in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; 2010. Abstract number 4823
4. U.S. News & World Report blog: Weight Gain Ups Breast Cancer Risk: 7 Ways to Avoid the Bulge. Deborah Kotz. http://health.usnews.com/health-news/blogs/on-women/2010/04/21/weight-gain-ups-breast-cancer-risk-7-ways-to-avoid-the-bulge