Energy balance represents the difference between energy intake, by eating, and energy expenditure, through physical activity.
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. This level of exercise is equivalent to about 45 minutes of brisk walking or 20 minutes of vigorous exercise per day.
The team of researchers, from Meharry Medical College and Vanderbilt-Ingram Cancer Center, both in Nashville, Tenn., together with colleagues at the Shanghai Cancer Institute in China, reported their findings in the June issue of the AACR journal Cancer Epidemiology, Biomarkers & Prevention.
"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.
Data were derived from the Shanghai Breast Cancer Study, in which women aged 25 to 64, 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 research data based on another study in Shanghai at the 95th AACR annual meeting, last year in Orlando, and published it in the April edition of Cancer Epidemiology, Biomarkers & Prevention* That study demonstrated that women who reported exercise participation in both adolescence and adulthood were 30 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.
*Matthews CE, Xu WH, Zheng W, Gao YT, Ruan ZX, Cheng JR, Xiang YB and Shu XO, "Physical Activity and Risk of Endometrial Cancer: A Report from the Shanghai Endometrial Cancer Study." Cancer Epidemiol Biomarkers Prev 2005;14:779-785.
Editors Note: A concurrent press release is being issued jointly by Meharry Medical College and Vanderbilt-Ingram Cancer Center.
Founded in 1907, the American Association for Cancer Research is a professional society of more than 24,000 laboratory, translational, and clinical scientists engaged in all areas of cancer research in the United States and in more than 60 other countries. AACR's mission is to accelerate the prevention and cure of cancer through research, education, communication, and advocacy. Its principal activities include the publication of five major peer-reviewed scientific journals: Cancer Research; Clinical Cancer Research; Molecular Cancer Therapeutics; Molecular Cancer Research; and Cancer Epidemiology, Biomarkers & Prevention. AACR's Annual Meetings attract nearly 16,000 participants who share new and significant discoveries in the cancer field. Specialty meetings, held throughout the year, focus on the latest developments in all areas of cancer research.