Scientific evidence is accumulating on physical activity as a means for the primary prevention of cancer. Nearly 170 observational epidemiologic studies of physical activity and cancer risk at a number of specific cancer sites have been conducted. The evidence for decreased risk with increased physical activity is classified as convincing for breast and colon cancers, probable for prostate cancer, possible for lung and endometrial cancers and insufficient for cancers at all other sites. Despite the large number of studies conducted on physical activity and cancer, most have been hampered by incomplete assessment of physical activity and a lack of full examination of effect modification and confounding. Several plausible hypothesized biological mechanisms exist for the association between physical activity and cancer, including changes in endogenous sexual and metabolic hormone levels and growth factors, decreased obesity and central adiposity and possibly changes in immune function. Weight control may play a particularly important role because links between excess weight and increased cancer risk have been established for several sites, and central adiposity has been particularly implicated in promoting metabolic conditions amenable to carcinogenesis. Based on existing evidence, some public health organizations have issued physical activity guidelines for cancer prevention, generally recommending at least 30 min of moderate-to-vigorous intensity physical activity on > or =5 d/wk. Although most research has focused on the efficacy of physical activity in cancer prevention, evidence is increasing that exercise also influences other aspects of the cancer experience, including cancer detection, coping, rehabilitation and survival after diagnosis.
Background:The recent decline in children’s active commuting (walking or biking) to school has become an important public health issue. Recent programs have promoted the positive effects of active commuting on physical activity (PA) and overweight. However, the evidence supporting such interventions among schoolchildren has not been previously evaluated.Methods:This article presents the results of a systematic review of the association between active commuting to school and outcomes of PA, weight, and obesity in children.Results:We found 32 studies that assessed the association between active commuting to school and PA or weight in children. Most studies assessing PA outcomes found a positive association between active commuting and overall PA levels. However, almost all studies were cross-sectional in design and did not indicate whether active commuting leads to increased PA or whether active children are simply more likely to walk. Only 3 of 18 studies examining weight found consistent results, suggesting that there might be no association between active commuting and reduced weight or body mass index.Conclusion:Although there are consistent findings from cross-sectional studies associating active commuting with increased total PA, interventional studies are needed to help determine causation.
Some farmer characteristics are associated with more safe behaviors, but efforts to encourage protective behaviors on farms should be broadly based in view of a lack of a single risk-taking profile among California farmers.
Purpose:To review systematically all publications of the effects of exercise on endogenous insulin-like growth factor (IGF) to clarify the nature of this association.Methods:We reviewed 115 research studies in humans by subgroup of population (age; sex; athletic training status), physical activity exposure (resistance vs. aerobic activity; duration of activity) and study design.Results:Fifty percent of studies reviewed found no difference in total circulating IGF-1 as a result of exercise; 37% showed an increase, and 13% observed decreases in IGF-1 levels with exercise. Age influenced the effects of exercise on IGF levels. Exercise appeared to decrease IGF-1 levels in children, but to increase levels in young adults. Similar results were found for IGFBP-3.Conclusions:It is not yet possible to determine if exercise affects IGF levels. Important methodologic differences among studies, as well as concerns about study quality, limit the ability to draw firm conclusions.
Epidemiologic studies of mesothelioma have focused primarily on occupational exposures to asbestos. Nonoccupational exposure to asbestos can be grouped into three main categories: paraoccupational (familial), neighborhood, and true environmental exposures. Elevated mesothelioma rates not attributable to occupational exposures have been observed in asbestos mining and manufacturing areas. Asbestos is one of the most dangerous environmental carcinogens because of the small dose known to cause mesothelioma and the rapid lethality of the disease once it develops. Further research is needed to characterize the contribution and risk profile for environmental asbestos and mesothelioma, and for the development of public health policy.
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