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Physical Activity and Prostate Cancer
Abstract & Commentary
By William B. Ershler, MD
Synopsis: In a large population-based, prospective cohort study, it was found that spending less than 50% of the day in a sedentary position, and increasing amounts of physical activity (e.g., walking or bicycling) appear to be associated with reduced rates of prostate-cancer development.
Source: Orsini N, et al. A prospective study of lifetime physical activity and prostate cancer incidence and mortality. Br J Cancer. 2009;101:1932-1938.
There has been some controversy on the role of physical activity and exercise in preventing cancer.1-4 With regard to prostate cancer, a review of 24 studies found inconclusive evidence for an association of physical activity and incident prostate cancer and concluded that more focused investigation was warranted.5 Subsequently, two case-control studies included an assessment of lifetime physical activity.6,7 One found a non-significant decrease in prostate cancer risk for lifetime recreational activity,6 whereas the contrary was found in the other study.7
To provide a more detailed and extensive evaluation of the relationship between lifetime physical activity and the incidence of prostate cancer, Orsini et al conducted a prospective cohort study of 45,887 men aged 45-79 years who were followed from January 1998 to December 2007 for prostate cancer incidence (n = 2735) and to December 2006 for its subtypes and for fatal (n = 190) prostate cancer. The study capitalized on a population-based cohort of Swedish men that was established in 1997 among men residing in Vastmanland and Orebro counties (central Sweden). Approximately half of the men (aged 45-79 years) residing in these communities agreed to participate, and they completed questionnaires pertaining to physical activity (walking, bicycling), body weight and measurements, education level, and medical conditions. The participants also were asked to provide information about their physical activity level at age 30 and 50 years, in addition to their current physical activity.
There was an inverse association between lifetime (average of age 30 and 50 years, and baseline age) total physical activity levels and prostate-cancer risk. Multivariate-adjusted incidence in the top quartile of lifetime total physical activity decreased by 16% (95% confidence interval [CI] = 2%-27%) compared with that in the bottom quartile. Also observed was an inverse association between average lifetime work or occupational activity and walking or bicycling duration and prostate-cancer risk. Compared with men who are sedentary for the majority of their time at work, men who spend half their time or less sitting experienced a 20% lower risk (95% CI = 7%-31%). The rate ratio linearly decreased by 7% (95% CI = 1%-12%) for total, 8% (95% CI = 0%-16%) for localized and 12% (95% CI = 2%-20%) for advanced prostate cancer for every 30 minutes per day increment of lifetime walking or bicycling in the range of 30 to 120 minutes per day.
Thus, not sitting for most of the time during work or occupational activity and walking or bicycling more than 30 minutes per day during adult life is associated with reduced incidence of prostate cancer. Although it is not immediately obvious why this would be the case, this carefully conducted, large epidemiological study confirms an association that seems quite reasonable. The size of the study and the carefully conducted methodology and analysis lends credence to the results. Nonetheless, it is an observational report and should not be interpreted as demonstrating that a sedentary lifestyle is causally related to prostate cancer development. Nonetheless, biological factors that are influenced by exercise and/or physical activity include certain hormones, including testosterone, insulin resistance, adiponectin levels, and insulin-like growth factors, and each of these is relevant to the pathogenesis of prostate cancer.
These findings have important public health implications but should be confirmed by additional investigation. A long-term randomized trial of a prescribed exercise program vs. activity as usual would go a long way in settling this issue. However, this would be methodologically challenging. Short of that, a large trial of prescribed exercise within a community, such as that provided in Sweden, for which excellent tumor registry data are available, might be considered. If appropriately selected participants maintained on such a long-term exercise program had significantly less prostate cancer than the general population, matched for all the appropriate characteristics, including age, diet, general health, etc., this would provide additional suggestive evidence that the risk of prostate cancer is modifiable by physical activity and exercise.
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