Epidemiological evidence continues to accumulate on the benefits of physical activity in relation to cancer risk, progression and mortality, physical activity and cancer. Recent studies suggest that sedentary behavior may independently affect cancer risk; they also focus on factors that may explain associations with physical activity and cancer activity, including cancer risk factors and whether associations exist for precancerous lesions. Despite enormous efforts to examine associations between physical activity and cancer, the literature is hindered by inconsistent assessment of physical activity across studies, and incomplete consideration of variation of effects across population subgroups for example, defined by body size, age or sex or tumors subgroups organ location, receptor status, or molecular subtype physical activity and cancer, and whether other factors explain study results.
Clearly, public health recommendations for appropriate changes in activity levels are needed; unfortunately, at this time, physical activity and cancer, we have no exact physical activity prescription to give to the public. The health benefits of participating in regular physical activity are well-documented, and include reductions in risk of cardiovascular disease, diabetes, osteoporosis, obesity, depression, physical activity and cancer, fatigue, and overall mortality [ 1 ].
Compelling evidence exists for inverse relationships between physical activity and risk of breast and colon cancers [ 2 ]. For these cancers, physical activity represents one of the few modifiable risk factors that can be recommended for risk reduction [ 2 ].
Evidence suggests that physical activity may also reduce the risk of endometrial and ovarian cancer, and may possibly reduce the risk of prostate and lung cancer [ 34 ]. Case-control and cohort studies have been the mainstay of study designs to examine associations between physical activity and cancer. Methods for data collection physical activity vary on approach interview, physical activity and cancer, self completed questionnaire, or occupational energy expenditureperiods of life covered, and whether key elements duration of each physical activity episode, physical activity and cancer, frequency of episodes, and intensity of activity are available.
It is also pertinent to distinguish between broad types of physical activity: Many studies estimate physical activity and cancer equivalents MET -hours of energy expenditure, a composite measure that captures intensity, frequency and duration of activity, using standard values specific to each activity and multiplying these values by the number of hours spent in the specific activity per week [ 5 ]. A number of meta-analyses have been published recently; these combine effect estimates from a series of studies to provide summary estimates of cancer risk.
Pooled analyses derive similar estimates of risk, but use the original data from the studies. A major challenge in combining results across studies of physical activity and cancer is that methods of quantifying physical activity vary. Most meta-analyses compare the group with the most physical activity however defined to that with the least activity sometimes inactive individuals; other times those with less than some predefined amount of activity.
Further, some studies examine recent activity, whereas others evaluate measures of long-term or lifetime activity; some include only recreational activity, whereas others focus on occupational activity or combine recreational and occupational activities.
Therefore, one must interpret results of these studies cautiously. Understanding the biological mechanisms underlying the associations between physical activity and cancer will provide needed insights that permit appropriate physical activity recommendations for reducing cancer risk.
A number of plausible candidate mechanisms have been proposed, some specific to one particular cancer; however the single mechanism or group of mechanisms that explains the associations between physical activity and lower cancer risk have yet to be established, physical activity and cancer.
For colon cancer, the major hypothesis is that physical activity lowers fecal bile acid concentrations and decreases gastrointestinal transit time. These mechanisms, which regulate sex steroid hormones, physical activity and cancer, are also potential mediators of the associations between physical activity and endometrial and ovarian cancers. Physical activity and cancer is highly plausible that several of these mechanisms act simultaneously, and that they interact synergistically to mediate the associations between physical activity and cancer.
This report provides a review of epidemiologic studies published between January and April on the associations between physical activity and cancer. An inverse association between physical activity and colon cancer risk has been consistently observed pms and vitamin b6 epidemiologic studies; however, the evidence for rectal cancer remains inconclusive [ 78 ].
In cohort studies, colon cancer risk reduction associated with physical activity is greater for men than for women, although case—control studies suggest similar benefits for men and women [ 10 ]. Whether physical activity preferentially protects against distal or proximal colon cancer is uncertain [ 11 ].
Stronger associations were observed for distal tumors than for proximal tumors. Boyle and colleagues et al. Importantly, this association lamictal and elevated biliruben independent of the amount of recreational physical activity reported by study participants [ 14 ]. For women who were less likely to hold jobs than men, only recreational physical activity was considered. Low physical activity was associated with increased colorectal cancer risk, consistent with previous studies.
In this study, the joint effects of physical activity and body size were assessed by comparing extremes. However, the interaction physical activity and cancer physical activity and body size was statistically significant only for proximal tumors. No association was observed for proximal colon cancer or rectal cancer. Genomic instability is known to drive several carcinogenic pathways [ 16 ]. Epigenetic silencing of gene expression, physical activity and cancer, primarily mediated by aberrant DNA methylation, has been implicated for colon cancer; however, its role in modifying the association between colon cancer and physical activity is not well understood [ 16 ].
Within a subset of the Netherlands Cohort Study population colorectal cancer cases and 4, controlsHughes and colleagues investigated the combined effects on colon cancer risk of CpG island methylator phenotype CIMP and physical activity [ 17 ]. For non-CIMP tumors, high and intermediate levels of physical activity were not associated with colorectal cancer risk High: The study lacked the statistical power to stratify by high school caps and gowns subsite proximal and distal colon cancer and rectal cancer.
An emphasis has been made on trying to identify risk factors for colon adenomas, which are considered a precursor lesion for colon cancer that is detected and removed during colonoscopy or sigmoidoscopy. One study examined whether CTNNB1 beta-cateninwhich is known to play a critical role in colorectal carcinogenesis and metabolic diseases, modifies the association between physical activity and colorectal cancer survival among participants in two prospective cohort studies the Nurses Health Study and the Health Professionals Follow-up Study conducted in the US [ 21 ].
The evidence for an association between physical activity and breast cancer has been classified as convincing [ 2 ]. Similarly, among postmenopausal women, those with higher amounts of recreational physical activity during their lifetimes have been shown to have lower breast cancer risk [ 2324 ].
Both premenopausal and postmenopausal women in this Shanghai study showed increasing breast cancer risk with increasing lifetime occupational sitting time and decreasing occupation energy expenditure [ 26 ]. Several other case-control studies published in the past 18 months have some shortcoming limited history of breast cancer, small sample size, hospital-based study design.
A population-based case-control study of 1, incident breast cancer cases and 1, healthy controls in Mexico only considered physical activity in the previous 12 months, with minimal although statistically significant decreases in breast cancer risk among both premenopausal and postmenopausal women [ 27 ]. A small hospital-based case-control study in Tunisia assessed lifetime total physical activity recreational, occupational and housework activityshowing marked reductions in postmenopausal, but not premenopausal breast cancer risk associated with lifetime physical activity [ 28 ].
The study lacked sufficient statistical power to assess risk among premenopausal women, a common limitation of studies. Thus, the association was limited to postmenopausal women. Similar risk reductions were observed among women who never used hormones, those who used hormones for less than 5 years and women who were currently taking estrogen only.
Associations physical activity and cancer not observed among other hormone use subgroups; however, despite the large size of this study, tests of homogeneity were not able to statistically demonstrate that hormone therapy modified the association between physical activity and breast cancer risk. As with colorectal cancer, an emphasis has been made on trying to detect risk factors earlier in the disease process. Women who engaged in 39— Hunger pangs and diabetes results suggest that the benefit of physical activity may be initiated early in the carcinogenic process and emphasize the importance of starting physical activity at young ages and maintaining physical activity throughout life, physical activity and cancer.
These associations were modified by BMI and hormone receptor status. Further, reductions in both breast cancer-specific and all-cause mortality were observed among women diagnosed with ER-positive, but not ER-negative, physical activity and cancer, tumors. Contrary to what was observed in the meta-analysis, Chen et al. The evidence showing that regular physical activity lowers endometrial cancer risk is accumulating, but is less convincing than that for breast or colon cancer [ 2 ].
Two case-control studies found similar results [ 3738 ]. Activity performed at younger and older adult ages produced similar risk reductions. Further, the inverse associations were strongest in obese and overweight women. The evidence for an association between physical activity and prostate cancer has been classified as probable [ 2 ].
An update to this review, based on 22 additional studies, indicates that the majority of recent research studies observed protective effects [ 39 ].
An issue that somewhat reduces our confidence in these estimates is that considerable heterogeneity between studies was observed.
Recent studies have attempted to address this issue by estimating risk within subgroups defined by smoking status. Due to sex differences in lung cancer pathology, risk factors and prognosis, current research has also begun to investigate the association for men and women separately [ 43 ].
Physical activity and cancer recent literature consists of small case-control studies [ 44 ] that suffer from an inability to examine risk in subgroups by histology, smoking status or sex reduced statistical powerphysical activity and cancer, and a survival bias in that rapidly fatal cases or those who are too ill to be interviewed physical activity and cancer excluded from the study population.
Existing literature on risk of ovarian cancer in relation to physical activity is inconclusive [ 2 ]. Physical activity has been studied in relation to renal cell carcinoma, in part because of the known deleterious effects of high body mass index and hypertension on the risk of renal cell cancer; however, no association has been established, physical activity and cancer.
Reductions in risk were greater for recreational than for other forms of activity and for activity performed later in life. A meta-analysis of 28 studies of pancreas cancer showed total lifetime physical activity and occupational activity were associated with reduced risk [ 51 ]. Non-significant reductions in risk were observed for recreational physical activity and transportation walking and cycling as a physical activity and cancer of commuting.
Significant heterogeneity was present across the studies, making it difficult to find a definitive answer. No associations were noted for other recreational activities or occupational activity, physical activity and cancer. Recently, three studies have investigated the association between NHL and physical activity.
Further, among prostate cancer patients, Richman et al. The latest lung cancer literature has focused on increasing cardiorespiratory fitness pension health and welfare plans manta 58 ]. To increase our understanding of these associations, it will be necessary to conduct studies that are optimally physical activity and cancer, collect detailed lifetime histories of physical activity, and examine the effects across different population subgroups.
By considering the potential, underlying biological mechanisms that nexium and iv dosing operative, it should be possible to refine study designs, questionnaires, and biomarker measures to enhance our understanding of the causal pathways that define the relationships between physical activity and cancer incidence, and to make our public health physical activity and cancer regarding physical activity more specific.
Although it is clear that recommendations for appropriate changes in physical activity levels are important public health messages, we still have no exact physical activity prescriptions to give the public generally for all cancers and specifically for individual cancers.
Further, we still need to be able to address the following questions: What are the ages when physical activity provides its greatest benefit? What types of activity will provide the greatest protection against cancer or enhance survival?
What activity patterns intensity, frequency, duration of activity are optimal? Can enhancements of the built environment facilitate participation in physical activity? No potential conflicts of interest relevant to this article were reported.
National Center for Biotechnology InformationU. Author manuscript; available in PMC Dec 1. See other articles in PMC that cite the published article. Abstract Epidemiological evidence continues to accumulate on the benefits of physical activity in relation to cancer risk, progression and mortality.
Introduction The health benefits of participating physical activity and cancer regular physical activity are well-documented, and include reductions in risk of cardiovascular disease, diabetes, physical activity and cancer, osteoporosis, obesity, depression, fatigue, and overall mortality [ 1 ].
Colorectal Cancer Colorectal Cancer Development An inverse association between physical activity and colon cancer risk has been consistently observed among epidemiologic studies; however, the evidence for rectal cancer remains inconclusive [ 78 ]. Breast Cancer Breast Cancer Development The evidence for an association between physical activity and breast cancer has been classified as convincing [ 2 ].
Other Cancer Sites Cancer Development Endometrial Cancer The evidence showing that regular physical activity lowers endometrial cancer risk is accumulating, but is less convincing than that for breast or colon cancer [ 2 ]. Prostate Cancer The evidence for an association between physical activity and prostate cancer has been classified as probable [ 2 ].
Ovarian Cancer Existing literature on risk of ovarian cancer in relation to physical activity is inconclusive peer support and mental illness 2 ]. Renal Cell Carcinoma Physical activity has been studied in relation to renal cell carcinoma, in part because of the known deleterious effects of high body mass index and hypertension on the risk of renal cell cancer; however, no association has been established.
Pancreatic Cancer A meta-analysis of 28 studies of pancreas cancer showed total lifetime physical activity and occupational activity were associated with reduced risk [ 51 ].