Local DiskModel PaperModel PaperModel Position Paper The Preventative Effects of Lifetime Exercise on Breast Cancer Audience: Undergraduate students in integrative physiologyBreast cancer is the most common cancer in women, except for skin cancer, and affects hundreds of thousands of women each year. In 2003 alone, the American Red Cross estimated that 175,000 new cases of invasive breast cancer were diagnosed and that 43,300 women died from the cancer (1). Reducing the risk of breast cancer is a goal for many in the health field in the hope of sparing as many women as possible from the pain and trauma associated with the disease. However, despite massive attention and thorough research surrounding breast cancer, prevention and risk reduction still remain a mystery today.In recent years, new studies have focused on the role that exercise plays in reducing breast cancer risk, but these studies have proven inconclusive. A large number of these studies support the claim that exercise reduces breast cancer risk, but some studies show exercise to have little or no effect on the risk (5). Table 1 outlines the lack of consensus between six of the major studies that have been published on exercise and its effects on breast cancer. Three studies support exercise as having a protective effect against breast cancer (2,8,9). The other three studies demonstrate either an increased risk of breast cancer with increased exercise (3, 4), or no relationship between the variables (7). These results are reported through file:///C|/Documents%20and%20Settings/Laurence%20Green...se/slidesOld/structureOfArgument1/examplePosition.html (1 of 12)10/24/2007 4:27:08 PMModel Paperepidemiolgic statistics called relative risks (RR) and odds ratios (OR). Both statistics represent the risk of developing a disease in a particular group of subjects relative to the risk in a referent, or control, group of subjects. In prospective observational studies on the association between exercise and breast cancer, the referent group is composed of sedentary subjects. This group is given the referent value of 1.0. For subjects who exercise, relative risk and odds ratio values are determined by calculating the following ratio:Number of exercising subjects who eventually develop breast cancer Number of sedentary subjects who eventually develop breast cancerRelative risks and odds ratios above 1.0 indicate an increased risk of developing breast cancer, while values below 1.0 indicate a decreased risk of developing the disease. For example, a relative risk of 1.6 in the Dorgan study represents a 60% increase in the risk of developing breast cancer among highly active subjects compared to sedentary subjects (4). In constrast, an odds ratio of .42 in the Bernstein study demonstrates a 58% decrease in the risk of developing breast cancer in highly active subjects compared to inactive participants (2). These two studies exemplify the lack of consensus on this issue. The contradictory findings exist for file:///C|/Documents%20and%20Settings/Laurence%20Green...se/slidesOld/structureOfArgument1/examplePosition.html (2 of 12)10/24/2007 4:27:08 PMModel Papermany reasons, including the complex natures of cancer and exercise physiology, but inconsistent research methods especially hinder resolution. Table 1. Studies that support breast cancer risk being reduced by exercise First author, year (Reference No.) Sample size & Design Subjects Methods Results Bernstein, 1994 (2) 545 incident cases, 545 controls; Case-control 545 with breast cancer and 545 control Interviews to gain lifetime histories of exercise OR .42 between > 3.8 hrs. of exercise and inactivity(decreased cancer risk) Rockhill, 1999 (8) 121,701; Cohort Registered nurses, aged 30-55 years Analyzed previous study; calculated lifetime and one-time measures of exercise RR .82 between > 7 hours and < 1 hour per week(decreased cancer risk) Thune, 1997 (9) 25,624; Cohort Women from Norway, aged 20 to 54 at entry Questionnaires about leisure and work activity RR .63 between regular exercisers and sedentary(decreased cancer risk) Studies that do not support breast cancer risk being reduced by exercisefile:///C|/Documents%20and%20Settings/Laurence%20Green...se/slidesOld/structureOfArgument1/examplePosition.html (3 of 12)10/24/2007 4:27:08 PMModel PaperCoogan, 1999 (3) 233 incident cases, 670 controls; Case-control Women with/w-out breast cancer in Cape Cod Interviews for information on job history; risk factors OR 1.7 between job of med/hi activity and control(increased cancer risk) Dorgan, 1994 (4) 2,321; Cohort evaluation Women aged 35-68 years at fourth examination Analyzed previous cardiovascular fitness study RR 1.6 between highest and lowest activity level(increased cancer risk) Paffenbarger, 1992 (7) 2370; Cohort College alumni, aged 40-50 Self-reported current physical activity levels RR .96 between >5 hrs sports play and non-activity(no significant effect) Though a consensus has not been reached regarding whether exercise reduces breast cancer risk, some research supports lifetime exercise as the key to reducing the risk of breast cancer (8). Lifetime exercise refers to physical activity levels that are maintained through the majority of life. Lifetime exercise differs from the common baseline measure of exercise used in many exercise and breast cancer studies, because a baseline measure takes into account only the level of exercise at one specific time in life. In contrast, lifetime exercise is a measure of the level of exercise throughout the duration of one's life. Researchers obtain lifetime measures by collecting data on as much of an individual's past exercise history as possible and then quantifying that history so it can be file:///C|/Documents%20and%20Settings/Laurence%20Green...se/slidesOld/structureOfArgument1/examplePosition.html (4 of 12)10/24/2007 4:27:08 PMModel Papercompared relative to other individual's histories. Measuring lifetime exercise can be more conclusive than obtaining a baseline measure because variables of breast cancer risk are averaged over an extended period of time. Variables of breast cancer risk, such as age at menses (onset of menstruation), intensity of chronic or long-term exercise, whether the woman has had children, consistency of regular exercise, and when regular exercise is begun during the woman's lifetime can influence how exercise affects breast cancer. Measuring lifetime exercise, for instance over a period of 30 to 40 years,