Physical activity and colon cancer

Heart disease and cancer, the major causes of mortality and morbidity in Western countries, have common risk factors. Exercise appears to reduce the risk of cardiovascular disease, but its role with respect to primary prevention of cancer has not been emphasized. Here we evaluate the epidemiological studies dealing with exercise and colon cancer. Despite the fact that different methods of assessing the amount of typical exercise of individuals and the different types of physical activity measured (occupational and recreational), there is remarkably consistent evidence that people who are highly physically active could be at a reduced risk of cancer of the colon. An analysis of case-control and cohort studies suggests that exercise might reduce the risk, at least in men, by up to one-third. We conclude that exercise has been overlooked as a potentially useful, effective, and acceptable method for reducing the risk of colon cancer.     

Physical activity and the risk of breast cancer

BACKGROUND: Because physical activity may affect hormonal concentrations and energy balance, we decided to investigate whether everyday exercise is related to the risk of breast cancer. METHODS: During 1974 to 1978 and 1977 to 1983, a total of 25,624 women, 20 to 54 years of age at entry, enrolled in health surveys and answered questionnaires about leisure-time and work activity. RESULTS: During a median follow-up of 13.7 years, we identified 351 cases of invasive breast cancer among the 25,624 women in the cohort. Greater leisure-time activity was associated with a reduced risk of breast cancer, after adjustments for age, body-mass index (the weight in kilograms divided by the square of the height in meters), height, parity, and county of residence (relative risk, 0.63; 95 percent confidence interval, 0.42 to 0.95), among women who exercised regularly, as compared with sedentary women (P for trend=0.04). In regularly exercising women, the reduction in risk was greater in premenopausal women than in postmenopausal women, and greater in younger women (<45 years at study entry) than in older women (> or =45 years) (relative risk, 0.38; 95 percent confidence interval, 0.19 to 0.79). In stratified analyses the risk of breast cancer was lowest in lean women (body-mass index, <22.8) who exercised at least four hours per week (relative risk, 0.28; 95 percent confidence interval, 0.11 to 0.70). The risk was also reduced with higher levels of activity at work, and again there was a more pronounced effect among premenopausal than postmenopausal women. CONCLUSIONS: Physical activity during leisure time and at work is associated with a reduced risk of breast cancer.     

Physical activity and cancer etiology: associations and mechanisms

OBJECTIVES: This paper reviews the epidemiologic data of associations between physical activity and cancer risk, describes potential mechanisms for a physical activity cancer link, and proposes future directions for research. METHODS: We reviewed English-language published papers on physical activity and cancer through Medline searches for epidemiologic studies, and through references on individual reports. We reviewed general texts on effects of exercise on human biology and applied the concepts to the biology of cancer in humans to describe potential mechanisms for a physical activity-cancer association. RESULTS: Considerable epidemiologic evidence has accrued linking increased physical activity with reduced occurrence of cancers of the breast and colon. The association between physical activity and cancers of other sites is unclear. Potential mechanisms for the association between physical activity and reduced risk for breast and colon cancer are varied: they range from bias due to physical activity's strong correlations with other health factors (e.g., diet, smoking, alcohol use, use of medications) to the metabolic effects resulting from increased physical activity and fitness, such as reduced obesity, hormonal and reproductive effects, mechanical effects, and enhancement of the immune system. CONCLUSIONS: The elucidation of biologic mechanisms for an association between physical activity and cancer may provide biological support for the association. It will contribute information to determine the type, frequency, and duration of exercise needed to maximize protection. This information will be needed before large-scale community interventions are begun, in order to choose the correct interventions for the desired effect of reduced incidence of the most common cancers.     

Physical activity and risk of breast cancer in the Framingham Heart Study

The authors analyzed data from the Framingham Heart Study to evaluate the association between physical activity and breast cancer risk. Physical activity was ascertained by a physician-administered questionnaire from 2,321 women at the fourth biennial examination conducted in 1954-1956. Breast cancers were identified by self-report, surveillance of admissions to Framingham Union Hospital, and review of death records; all but one were histologically confirmed. During 28 years of follow-up, 117 breast cancer cases were diagnosed among the 2,307 women with data on physical activity and reproductive history (a potential confounder). Analysis was performed using Cox proportional hazards models with age as the underlying time variable. Models were adjusted for age at physical activity assessment, menopausal status, age at first pregnancy, parity, education, occupation, and alcohol ingestion. We observed a gradient of increasing risk of breast cancer with increasing physical activity (trend p = 0.06). The relative risk for women in the highest versus lowest activity quartile was 1.6 (95% confidence interval 0.9-3.0; p = 0.13). Although both moderate-to-heavy leisure and occupational activities were associated with an increased risk, the association was marginally significant only for leisure activity (p = 0.06). Our findings do not support a protective effect of physical activity during adulthood for breast cancer, but suggest an increased risk among more active women.     

Physical activity and risk of colorectal cancer in men and women

We examined the association between self-reported occupational and recreational physical activity and the subsequent risk of colorectal cancer in a population-based cohort in Norway. During a mean follow-up time of 16.3 years for males and 15.5 years for females, 236 and 99 colon cancers and 170 and 58 rectal cancers were observed in males and females, respectively, among 53,242 males and 28,274 females who attended the screening between 1972 and 1978. Physical activity at a level equivalent to walking or bicycling for at least four hours a week during leisure-time was associated with decreased risk of colon cancer among females when compared with the sedentary group (RR = 0.62, 95% CI 0.40-0.97). Reduced risk of colon cancer was particularly marked in the proximal colon (RR = 0.51, 95% CI 0.28-0.93). This effect was not observed for occupational physical activity alone, probably due to a narrow range of self-reported physical activity at work among females. However, by combining occupational and recreational physical activity we observed an inverse dose-response effect as increasing total activity significantly reduced colon cancer risk (P for trend = 0.04). Among males 45 years or older at entry to the study, an inverse dose-response effect was observed between total physical activity and colon cancer risk (P for trend = 0.04). We also found in males a stronger preventive effect for physical activity in the proximal as compared to distal colon. In addition, we found a borderline significant decrease in colon cancer risk for occupational physical activity in males 45 years or older when compared to the sedentary group (RR = 0.74, 95% CI 0.53-1.04). All results were adjusted for age, body mass index, serum cholesterol and geographic region. No association between physical activity and rectal cancer was observed in males or females. The protective effect of physical activity on colon cancer risk is discussed in regard to energy balance, dietary factors, age, social class, body mass index and gastrointestinal transit time.     

Physical activity and colon cancer: a public health perspective

We have studied the action of peripheral blood lymphocytes (PBLs) and intrathyroidal lymphocytes (ITLs) on the biochemical and hormonal metabolism of autologous thyrocytes cultured in follicles in a collagen gel. The production of tumour necrosis factor alpha (TNF-alpha) in culture was also measured. Thyroid tissues and lymphocytes were obtained from ten patients with Graves' disease and from five control subjects. Lymphocyte-induced cytotoxicity was evaluated in autologous thyrocytes cultured in a collagen gel by several tests; neutral red uptake, lactate dehydrogenase activity and glutathione level. Hormonal metabolism was assessed by evaluating tri-iodothyronine (T3) and total cAMP production under TSH stimulation. TNF-alpha levels were measured in supernatants after 5 days of coculture. PBLs altered biochemical metabolism, T3 synthesis and cAMP production in autologous thyroid follicles. These inhibitions were greater than those obtained with ITLs. No difference was seen between cells obtained from patients with Graves' disease and those from normal subjects. TNF-alpha levels secreted by PBLs were higher than those secreted by ITLs. The concentrations of this cytokine decreased in coculture. Significant correlations were observed between the decrease in biochemical and hormonal parameters and TNF-alpha levels. Exogenous TNF-alpha and high doses of interferon gamma inhibited follicle metabolism, especially hormone secretion. In conclusion, thyrocytes cultured in follicles provide a more sensitive model than monolayer cultures for analysis of lymphocyte-induced interactions. Lymphocytes gradually inhibit the biochemical and hormonal metabolism of autologous thyroid follicles depending on the isolation method. These alterations may be particularly attributed to TNF-alpha secreted by lymphocytes. The cytokine-induced inhibition of thyroid hormonal function apparently involves the adenylate cyclase system.     

Improving the health profile: decreasing risk for cancer through primary prevention

Cancer is the second leading cause of death among adults in the United States. Trends indicate that the incidence of all cancers has increased since 1973. It is currently estimated that 1 in 3 Americans now living will develop the disease. Cancer accounts for 11% of all health care costs, and its devastating physical and emotional consequences are far reaching. Despite these grim statistics, there is hope for decreasing this huge burden. Nearly two thirds of all cancers are related to life style choices, such as tobacco use, dietary factors, and exercise; therefore, the opportunity exists to reduce cancer risk greatly. The article presents an overview of major cancers and strategies for primary prevention of those cancers that are most amenable to risk reduction.     

Tamoxifen for the primary prevention of breast cancer: a review and critique of the concept and trial

This paper has reviewed the rationale for and design of the NSABP Breast Cancer Prevention Trial and has provided a brief critique of the philosophy of chemoprevention of breast cancer and of certain practical aspects of the trial design. If the assumptions and estimates from the trial protocol are correct, the net benefit of the trial will be moderately large and positive (50 to 77 events prevented). However, over 500 women per year will be treated with tamoxifen unnecessarily. Recalculation of the net-benefit table using another set of reasonable assumptions regarding risks and the trial assumptions regarding benefits shows a negative effect to a small positive effect overall (-17 to 8 events). If the probability of adverse ocular events is included in the net-benefit equations, it appears that more harm than good will result from the intervention. In the face of the uncertainty regarding the net benefit of the trial, ranges of these risks and benefits should be provided to both potential and enrolled participants. The lack of significant benefit to participants seen with the recalculations may raise the question of whether the trial should continue as designed. One option would be to limit trial participation to postmenopausal women only, since 1) breast cancer is more common in postmenopausal women, 2) tamoxifen is more effective in postmenopausal women, 3) cardiovascular disease is more common in postmenopausal women, and 4) reductions in cholesterol levels and preservation of bone mass have only been documented in postmenopausal women (11, 27). Even in this case, however, the fundamental philosophical question of whether large numbers of healthy women should be "treated" with a toxic drug for the primary prevention of a rare event remains.     

Physical activity and aging

About a third of the initial muscle volume is lost during human life. This decline in muscle mass is responsible for impaired muscle strength, physical frailty, falls, impaired mobility, and functional decline. The age-related loss in muscle mass accounts for the age-associated decreases in basal metabolic rate, oxygen consumption, glucose utilisation, and bone density. Several of the anatomical and physiological changes in sedentary people, commonly attributed to primary aging processes, are in fact the consequence of lack of exercise. Recent studies show that strategies to maintain muscle strength and mass among the elderly (like regular exercise training) are most important for their functional independence.     

Physical activity in usual occupation and risk of breast cancer (United States)

OBJECTIVE: To identify whether the cause, site of ductal obstruction, and characteristics of fluid aspirates are associated with the cryosurvival and fertility after thawing of sperm obtained during reconstruction of the excurrent ducts with microsurgical epididymal sperm aspiration, vasal sperm aspiration, or both. DESIGN: Prospective study. SETTING: Andrology center at a tertiary care institution. PATIENT(S): Men undergoing reconstruction of the excurrent duct and sperm aspiration (n = 42) or microsurgical epididymal sperm aspiration (n = 11). INTERVENTION(S): Sperm were tested for an association with the cause and site of obstruction. Fertilization and pregnancy rates after sperm aspiration and intracytoplasmic sperm injection (ICSI) were evaluated for fresh and frozen aspirates. MAIN OUTCOME MEASURE(S): Motile sperm count and percentage motility after thawing. RESULT(S): The motile sperm count before freezing was significantly higher in the caput epididymis than in the corpus. The motile sperm count before freezing was related inversely to the distance from the caput where the sperm were aspirated. Sperm from clear and opaque fluid aspirates had better percent motility than those from cloudy and creamy fluid aspirates. High fertilization and pregnancy rates were achieved using both fresh and frozen epididymal sperm. CONCLUSION(S): None of the factors studied was associated with cryosurvival of aspirated epididymal or vasal spermatozoa. Because motility is low after thawing, these specimens are best used with ICSI.     

Skin cancer prevention and screening

Prevention and early detection of skin cancers are crucial to reducing morbidity and mortality. Armed with the above information and with some experience, the primary care physician can understand risk factors and recognize common benign and malignant skin tumors. This allows the primary care physician to play a key role in teaching patients about skin cancer prevention and in screening patients for skin cancers.     

The prevention of cancer

The purpose of this review is to summarize recent functional and structural findings regarding non-collagenous matrix proteins in bone and teeth, to compare gene locations for bone and tooth matrix proteins with loci for hereditary skeletal diseases, and to present several provocative hypotheses which integrate this new information into a physiological context. Hypothesis I proposes that the molecular composition of rapidly deposited and mineralized woven bone, as well as the responsiveness of cells synthesizing woven bone to stimuli, is different from that for more slowly synthesized lamellar bone, implying the existence of distinctive osteogenic mechanisms. This review of recent research strongly supports this proposal. Briefly, the protein composition of woven bone matrix is enriched in acidic phosphoproteins BAG-75 and BSP, which are not expressed in lamellar bone, which is itself enriched in osteocalcin. De novo deposition and mineralization of woven bone occurs faster than in lamellar bone by means of a matrix-vesicle-assisted mechanism. Deposition of woven bone occurs at sites experiencing biomechanical strains higher than those experienced by lamellar bone. In addition, woven bone in metaphyseal regions is more susceptible to osteoclastic resorption after space flight, ovariectomy, and loss of weightbearing than is lamellar bone. Finally, osteoprogenitor cells responsive to parathyroid hormone reside in the metaphyseal region of long bones. Taken together, these findings suggest that Hypothesis I represents a useful paradigm for future studies. Specific functions mediated by most individual bone and tooth matrix proteins remain uncertain. A review of current literature suggests that the functionality of skeletal matrix proteins is expressed through specific binding sites composed of particular species-conserved structural motifs (Hypothesis 2). Examples include the previously recognized Asp-Ser-Ser motif of dentin phosphophoryns and the gamma-carboxyglutamic acid motif of matrix GLA protein and osteocalcin. A new polyacidic amino acid motif composed of consecutive Asp and Glu residues (n > 7) was defined in extracellular matrix components osteopontin, bone sialoprotein, and bone acidic glycoprotein-75 on the basis of strong functional analogies with similar polyacidic stretches in divalent metal storage proteins of the endoplasmic reticulum and sarcoplasmic reticulum. These structural motifs represent prime targets for future structure-function studies in vivo and in vitro.