Exercise and diet can significantly reduce risk
By David Dunaief, M.D.
October is Breast Cancer Awareness Month, and everyone agrees that awareness is crucial. The incidence of invasive breast cancer in 2020 in the U.S. is estimated to be over 270,000 new cases, with approximately 40,000 patients dying from this disease each year (1).
A primary objective of raising awareness is to promote screening for early detection. But at what age should screening start and how often should we be screened?
Here is where divergence occurs; experts can’t agree on age and frequency. The U.S. Preventive Services Task Force recommends mammograms every other year, from age 50 through age 74 (2). The American College of Obstetricians and Gynecologists recommends consideration of beginning mammograms at 40, but starting no later than 50, and continuing until age 75. They encourage a process of shared decision-making between patient and physician (3).
Just as important as screening is prevention, whether it is primary, preventing the disease from occurring, or secondary, preventing recurrence. Potential ways of doing this may include lifestyle modifications, such as diet, exercise, obesity treatment and normalizing cholesterol levels. Additionally, although results are mixed, it seems that bisphosphonates do not reduce the risk of breast cancer.
Bisphosphonates include Fosamax (alendronate), Zometa (zoledronic acid) and Boniva (ibandronate) used to treat osteoporosis. Do they have a role in breast cancer prevention? It depends on the population, and it depends on study quality.
In a meta-analysis involving two randomized controlled trials (RCTs), FIT and HORIZON-PFT, results showed no benefit from the use of bisphosphonates in reducing breast cancer risk (4). The study population involved 14,000 postmenopausal women from ages 55 to 89 women who had osteoporosis, but who did not have a personal history of breast cancer. In other words, the bisphosphonates were being used for primary prevention.
In a more recent meta-analysis of 10 studies with over 950,000 total participants, results showed that bisphosphonates did indeed reduce the risk of primary breast cancer in patients by as much as 12 percent (5). However, when the researchers dug more deeply into the studies, they found inconsistencies in the results between observational and case-control trials versus RCTs, along with an indication that longer-term use of bisphosphonates is more likely to be protective than use of less than one year.
Randomized controlled trials are better designed than observational trials. Therefore, it is more likely that bisphosphonates do not work in reducing breast cancer risk in patients without a history of breast cancer or, in other words, in primary prevention.
We know exercise is important in diseases and breast cancer is no exception. In an observational trial, exercise reduced breast cancer risk in postmenopausal women significantly (6). These women exercised moderately; they walked four hours a week over a four-year period. If they exercised previously, but not recently, five to nine years ago, no benefit was seen. The researchers stressed that it is never too late to begin exercise.
Only about one-third of women get the recommended level of exercise every week: 30 minutes for five days a week. Once diagnosed with breast cancer, women tend to exercise less, not more. We need to expend as much energy and resources emphasizing exercise as a prevention method as we do screenings.
Contrary to popular belief, soy may be beneficial in reducing breast cancer risk. In a meta-analysis (a group of eight observational studies), those who consumed more soy saw a significant reduction in breast cancer compared to those who consumed less (7). There was a dose-response curve among three groups: high intake of >20 mg per day, moderate intake of 10 mg and low intake of <5 mg.
Those in the highest group had a 29 percent reduced risk, and those in the moderate group had a 12 percent reduced risk when compared to those who consumed the least. In addition, higher soy intake has been associated with reduced recurrence and increased survival for those previously diagnosed with breast cancer (8). Why have we not seen this in U.S. trials? The level of soy used in U.S. trials is a fraction of what is used in Asian trials. The benefit from soy is thought to come from isoflavones, plant-rich nutrients.
Western vs. Mediterranean diets
A Mediterranean diet may decrease the risk of breast cancer significantly.
In an observational study, results showed that, while the Western diet increases breast cancer risk by 46 percent, the Spanish Mediterranean diet has the inverse effect, decreasing risk by 44 percent (9). The effect of the Mediterranean diet was even more powerful in triple-negative tumors, which tend to be difficult to treat. The authors concluded that diets rich in fruits, vegetables, beans, nuts and oily fish were potentially beneficial.
Hooray for Breast Cancer Awareness Month stressing the importance of mammography and breast self-exams. However, we need to give significantly more attention to prevention of breast cancer and its recurrence. Through potentially more soy intake, as well as a Mediterranean diet and modest exercise, we may be able to accelerate the trend toward a lower breast cancer incidence.
(1)breastcancer.org.(2)uspreventiveservicestaskforce.org. (3) acog.org. (4) JAMA Inter Med online. 2014 Aug. 11. (5) Clin Epidemiol. 2019; 11: 593–603. (6) Cancer Epidemiol Biomarkers Prev online. 2014 Aug. 11. (7) Br J Cancer. 2008;98:9-14. (8) JAMA. 2009 Dec 9; 302(22): 2437–2443. (9) Br J Cancer. 2014;111:1454-1462.
Dr. David Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, visit www.medicalcompassmd.com.