Can a person with a normal level body mass index be at an increased risk for breast cancer?
Obesity is an epidemic that has been associated with an increased risk of several different cancers including: breast, ovarian, endometrial (uterine), liver, kidney, gallbladder, thyroid and colorectal cancer. A previous population-based study using Body Mass Index (BMI) and cancer incidence data estimated that, in 2012 in the United States, about 28,000 new cases of cancer in men (3.5%) and 72,000 in women (9.5%) were due to being overweight or obesity ¹. Another study summarizing worldwide cancers attributable to overweight and obesity reported that, compared with other countries, the United States had the highest numbers attributable to overweight and obesity for colorectal cancer, pancreatic cancer, and postmenopausal breast cancer ².
However, in a recent study at Memorial Sloan Kettering, Dr. Neil M Iyengar and his colleagues questioned the association between postmenopausal breast cancer risk in women and a normal BMI but with increased body fat. He conducted a secondary analysis of a subset of patients from the Women’s Health Initiative clinical trial, which included over 3000 patients. The analysis of the study included postmenopausal women ages 50-79 years old. Body fat levels were measured using dual-energy x-ray absorptiometry (DEXA scan) at baseline and at 1, 3, 6, and 9 years. The results of their findings were published recently in JAMA Oncology in Dec 2018.
The results showed that the risk of invasive breast cancer was greater in postmenopausal women with the highest whole-body fat and trunk fat mass levels. They also measured levels of circulating metabolic and inflammatory factors and found these to be altered in women with breast cancer.
Even though obtaining a low BMI is the goal for women to keep and maintain a healthy lifestyle and to help reduce the risk of cancer, this study brings forth an important aspect of optimal health, the body fat level. A standard way of measuring body fat is with a DEXA scan, as performed in this study. DEXA scans are typically used to measure bone density. However, they can be costly and some are not covered by insurance. A simpler, but less accurate alternative is the use of bathroom scales. With the at-home body composition scales, many factors can alter the results, including hydration, diet, and exercise. However, if you are wanting a quick read of your body fat percentage, these scales can help with that curiosity and motivate for a healthier lifestyle.
When speaking in terms of BMI and body fat, the two terms are often used interchangeably, but have different meanings. The downfall of calculating an individual’s BMI is not taking into account how much weight is muscle and how much weight is fat. For an active adult or even an athlete, BMI can misrepresent health and fitness and in fact, show a higher than normal BMI. If you are just starting on a journey of being healthy and staying active, BMI is a good measurement. You can calculate your BMI at this website: BMI Calculator. Otherwise, body fat percentage is a more accurate representation of healthy weight loss.
Overall, it is important to be proactive in eating healthy, staying active, maintaining a healthy lifestyle in reducing cancer risk and having a prolonged life. Consult your physician for ways to maintain a healthy lifestyle.
1. Arnold M, Pandeya N, Byrnes G, et al. Global burden of cancer attributable to high body-mass index in 2012: a population-based study. Lancet Oncology 2015; 16(1):36-46. [PubMed Abstract]
2. Whiteman DC, Wilson LF. The fractions of cancer attributable to modifiable factors: A global review. Cancer Epidemiology 2016; 44:203-221. [PubMed Abstract]