Women who exercise more and keep their weight under control may dramatically reduce their odds of developing breast cancer, a population-based study by a team of investigators at Meharry Medical College and the Vanderbilt-Ingram Cancer Center suggests.
The researchers, along with colleagues at the Shanghai Cancer Institute in China, report a strong link between "energy balance" and breast cancer risk in the June issue of Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research (AACR). Energy balance represents the difference between energy intake (eating) and energy expenditure (activity).
Breast cancer will be diagnosed in more than 211,000 American women this year, and will claim almost 41,000 lives, making it the second leading cancer killer among women in the United States. While certain factors are known to increase breast cancer risk – including family history and age of first menstruation and onset of menopause – there is a need for more information about those risk factors that can be modified.
Women with low levels of physical activity and higher body mass index levels (weight divided by height) were at more than twice the risk of developing breast cancer than women who undertook approximately three metabolic equivalent hours (MET) per day, per year, of exercise, and had lower BMI levels, the researchers found. This level of exercise is equivalent to about 45 minutes of brisk walking or 20 minutes of vigorous exercise per day.
"Given the substantial level of weight gain in industrialized countries in the last two decades," said lead author Alecia S. Malin, DrPH, CHES, assistant professor of Surgery at Meharry and assistant professor of Medicine at Vanderbilt, "there is great interest in understanding the influence of energy balance on cancer risk, and in developing preventive measures that can effectively minimize excess risk. Our study suggests that the promotion of behavior patterns that optimize energy balance – weight control and increased physical activity – may be a viable option for breast cancer prevention."
She further points out that the anti-cancer effect of lowering caloric intake alone, demonstrated in animals, is not generally considered to be a feasible strategy for cancer prevention in humans. Indeed, her team's results show that greater energy intake alone was not associated with an increased risk of breast cancer among physically inactive women, suggesting that it is the combination of exercise and weight control that is important.
Data were derived from the Shanghai Breast Cancer Study, in which women 25-65 years old who were newly diagnosed with breast cancer, along with a random sample of healthy controls, were enrolled between August 1996 and March 1998.
Information was gleaned from in-person interviews of 1,459 breast cancer cases and 1,556 controls. The body mass index of these women was calculated based on measurements taken by the interviewers of their weight, circumference of waist and hips, and height.
"This direct approach enabled us to overcome the primary problem affecting the accuracy of energy balance assessments," said Malin. "Self-reporting leads to under-reporting, particularly when overweight people account for their own energy intake. They have a tendency to give socially acceptable answers, or to respond based on their desire to lose weight and improve their eating habits."
Extrapolation of the results for Westerners, Malin noted, should take into account the inherent differences in the relationship between BMI levels and disease risk that appear to exist between Western and Asian women. A 25 kg/m2 body mass index among Western women is considered to be normal weight, while a BMI of 25 kg/m2 among Asian women is considered to be in the overweight category and was associated with an increased breast cancer risk in this study.
A co-author of the article, Charles E. Matthews, Ph.D., of Vanderbilt, presented similar findings involving endometrial cancer at the 95th AACR annual meeting. That study, also involving a cohort of women in Shanghai, demonstrated that women who reported exercise participation in both adolescence and adulthood were 30 percent to 40 percent less likely to develop endometrial cancer than women who reported no exercise in either period of their lives. Common activities, including household chores and daily walking, were also found to reduce endometrial cancer risk by about 30 percent. That study was published in the April edition of Cancer Epidemiology, Biomarkers & Prevention.
The breast cancer study is an example of the fruitful collaboration among scientists, physicians and others at Meharry and Vanderbilt-Ingram. The institutions have worked together since 1999 through a formal partnership, funded by the National Cancer Institute to promote meaningful collaboration between NCI-designated Comprehensive Cancer Centers and historically black medical colleges.
The partnership, facilitated through the Meharry-Vanderbilt Alliance, is engaged in interdisciplinary basic, translational and clinical research and cancer control activities, especially those aimed at reducing the disproportionate cancer incidence, morbidity and mortality among minorities and underserved groups.