Physical activity and cancer
The past two decades have seen a substantial amount of evidence supporting the beneficial role of physical activity for cancer survivors. More recent and clinically relevant advantages of physical activity for cancer survivors include a reduced risk of recurrence and mortality. The majority of cancer survivors are not getting sufficient amounts of physical activity, and new research suggests that survivors spend an overwhelming majority of their waking hours in sedentary pursuits and research is currently ongoing to determine the adverse health consequences of such behaviours. Objectively assessed (i.e., accelerometer) physical activity and sedentary time data has provided confirmation that the activity and sedentary behaviour profiles of cancer survivors are cause for concern. Ultimately, cancer survivors who are physically active are significantly less likely to have a cancer recurrence, less likely to die from their cancer, and more likely to live longer than survivors who are not physically active. Thus it can be concluded that all cancer survivors should try to be as physically active as possible. While data have yet to emerge, one can feasibly speculate that a physically active (and less sedentary) population of cancer survivors would translate into a substantial cost savings to the healthcare system.
Cancer is one of the most distressing and debilitating diseases of our time. The National Cancer Institute Office of Cancer Survivorship states that an individual is a cancer survivor from the time of diagnosis, through the balance of his or her life. The American Cancer Society (ACS) estimated that there are almost 14 million cancer survivors alive in the United States. The ACS also estimated that that over 1.6 million new cases of cancer (excluding skin cancer) are expected to be diagnosed in 2013 with 580,000 people dying from their cancer. It is the leading cause of death followed by heart disease and stroke. The global economic impact of death and disability from cancer was estimated at $895 billion in 2008. Prostate, breast, lung, and colorectal cancer were expected to account for 50% of all new cancer cases in the United States.
There are over 100 types of cancer and individuals diagnosed with cancer often undergo several types of specific cancer treatments (e.g., surgery, chemotherapy, radiation therapy, hormonal therapy). Cancer and its extensive treatments can take a significant toll on the physical and psychosocial health and well being of cancer survivors. Although these treatments have been shown to improve survival rates, cancer survivors are also at increased risk for many acute, chronic, and late effects of their disease and treatments, including a recurrence of another type of cancer, second cancers, cardiac dysfunction, weight gain, bone loss, lymphedema, arthralgias, cognitive dysfunction, menopausal symptoms, reduced health-related quality of life (HRQoL), fatigue, and psychosocial distress. The adverse side effects of treatments associated with cancer have spurred a major research effort into strategies to alleviate and minimize treatment effects; hasten recovery after treatments; improve long-term HRQoL; and reduce the risk of disease recurrence, other chronic diseases, and premature death. Many survivors live with the effects of cancer, require repeated active treatment and have continuing need for cancer care resources and support services. Thus cancer survivors represent an important target population for health promotion interventions.
Traditionally, cancer survivors were offered informational and educational nonbehavioral counselling, psychotherapy, social support, and/or other nontraditional therapies such as music or art therapy. Although somewhat effective, these therapies are largely psychological in nature and unlikely to address the physical and functional problems encountered by breast cancer survivors (e.g., fatigue). Throughout the past two decades, physical activity has emerged a a powerful rehabilitation modality for cancer survivors.
Physical activity and cancer
Substantial evidence indicates individuals can accrue a number of health benefits as a result of regular participation in physical activity, such as improvement in psychosocial health, cardiovascular fitness, muscular strength and endurance, maintenance of a health body weight, and reduced risk of chronic conditions including cardiovascular disease, diabetes, and cancer. Evidence now strongly suggests that physical activity plays a critical role across the cancer trajectory; from prevention, through to post diagnosis (on treatment), and well into survivorship. A growing number of high quality randomized controlled trials with cancer survivors over the past several decades indicate that physical activity may have a positive effect on a number of health-related quality of life (HRQoL) indices including improvement in muscular strength, aerobic fitness, fatigue, cancer specific concerns, functional quality of life, anxiety, and self-esteem.
More recently, exciting evidence has emerged suggesting that cancer survivors who are physically active after their treatments are less likely to have a cancer recurrence, less likely to die from their cancer, and more likely to live longer than survivors who are not physically active. One cohort study of almost 3,000 breast cancer survivors found that higher levels of post treatment physical activity were associated with reduced risks of breast cancer recurrence, breast-cancer-specific mortality, and all-cause mortality. Research also suggested that women who decreased their physical activity levels after they were diagnosed with breast cancer had a four times greater risk of dying when compared with women who started physical activity after their diagnosis. Similar data have emerged from colon cancer survivors. In the CALGB 89803 cohort, researchers found that physical activity may reduce the risk of colon cancer recurrence. It was found that survivors who walked as little as six hours per week at a moderate intensity had a 47% improvement in disease-free survival when compared with colon cancer survivors who did not walk. These studies found that the amount of physical activity done before being diagnosed with colon cancer was not nearly as important as the amount of physical activity performed after diagnosis and treatment.
Physical activity behaviours of cancer survivors
Despite the accumulating evidence documenting the associated benefits of physical activity for cancer survivors, the majority of survivors are not meeting the minimal amounts of physical activity required for health benefits (e.g., 30 minutes of at least moderate intensity activity on 5 days of the week, and/or more recently, the American College of Sports Medicine cancer survivor guideline of at least 150 minutes of at least moderate intensity activity per week). Published data from a wide variety of cancer groups (e.g., breast, colorectal, non-Hodgkin's lymphoma, endometrial, kidney, bladder, rural breast) has consistently demonstrated that physical activity behaviour decreases as a survivor moves through the cancer trajectory (i.e., pre diagnosis, on treatment, post treatment). Collectively, it appears that approximately 20-25% of survivors were achieving physical activity guidelines after, which is significantly lower the 30-35% meeting guidelines prior to being diagnosed with cancer. However, the aforementioned research pertaining to the physical activity behaviour rates of cancer survivors has specifically used self-report measures of physical activity.
Analysis of objectively measured physical activity (i.e., accelerometer) has suggested that the physical activity behaviour rates of cancer survivors may be substantially inflated. To date, two studies have utilized objectively-determined physical activity data when exploring physical activity-related health outcomes among cancer survivors. The data examined by these studies are drawn from two waves of the National Health and Nutrition Examination Survey (2003-04 and 2005-06), in which accelerometer data were available for a heterogenous sample of self-reported cancer survivors. Among the 111 self-reported breast cancer survivors from the NHANES database, Lynch et al. reported that survivors were engaging in an average of only 3.7 minutes of moderate-to-vigorous intensity physical activity per day. Similarly, among 103 prostate cancer survivors, the average time per day spent engaging in moderate-to-vigorous physical activity was 6.0 minutes. Research initiatives are currently underway (by our group, and others) to assess objective physical activity behaviours of cancer survivors and related health outcomes. Given this evidence (poor physical activity compliance) and the clinically relevant advantages of physical activity for cancer survivors, it is clearly evident that physical activity motivation and adherence are important issues to consider.
Sedentary behaviour and cancer survivors
Few studies have considered sedentary behaviour in the cancer context, despite its adverse association with mechanisms operative in carcinogenesis. Evidence has started to emerge suggesting that too much sedentary behavior (i.e., sitting) can also have adverse health consequences for cancer survivors which are independent of physical activity. We recently proposed a new cancer survivorship research agenda focusing on sedentary behaviour among cancer survivors.
Sedentary behaviour has deleterious health consequences that are distinct from the beneficial effects of physical activity. Sedentary behaviour has been independently associated with chronic disease-related risk factors such as adiposity, insulin resistance, and inflammation in healthy adults. These factors are also hypothesized to be operative in the development and progression of some cancers. The aforementioned studies by Lynch et al. indicated that during an average accelerometer wear-time period, breast and prostate cancer survivors spent approximately 9.5 hours per day in sedentary pursuits (e.g., sitting, driving). The limited data to date suggests that sedentary behaviours among cancer survivors have been associated with higher body mass index, de novo ischemic heart disease risk, and poorer HRQoL.
The benefits of using accelerometers in understanding the physical activity behaviours has extended to the study of sedentary behaviour and our research team has currently launched initiatives designed to determine the objectively assessed sedentary time of cancer survivors, and the associated health consequences.
Despite the convincing evidence of the supportive role of physical activity for cancer survivors, the overwhelming majority of cancer survivors are still not meeting the recommended amounts of physical activity required for the accrual of health benefits (e.g., psychosocial, physical, reduced recurrence and mortality). Recent data from objective physical activity monitors (i.e., accelerometers) suggested that the proportion of physically active cancer survivors is much lower than previously believed. While the benefits of physical activity for cancer survivors has been well documented, clinicians and researchers need to continue to examine practical, sustainable, and economically viable health promotion interventions designed to facilitate physical activity and reduce sedentary behaviour among cancer survivors. This is particularly relevant for those with diabetes, for whom exercise should already be a regular part of their treatment regimen.
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