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| Reduction of Individual Cancer Risk by Physical Exercise: Epidemiological Studies, Molecular Mechanisms and Practical Recommendations pp. 83-124 |
$25.00 |
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Authors: Andreas Willer , Paul La Rosée and Susanne Saussele
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Abstract:
About 50 % of all human cancers in the developed world are preventable by lifestyle changes. These lifestyle changes, which are required to reduce the risk of getting cancer, represent modifiable risk factors for malignant but also other chronic diseases. Currently, promoted strategies for cancer prevention include reduction of tobacco consumption, increased physical activity, weight control, a balanced diet, limited alcohol consumption, avoidance of excessive UV-radiation and participation in medical prevention programs. Among these recommendations, increased physical activity is expected to play a central role for risk reduction, since it is likely to have beneficial impact also on other factors such as tobacco use, weight control, diet and alcohol consumption.
In fact, increasing evidence indicates that physical exercise is inversely related to the individual risk for the most common human cancers. However, the evidence is hampered by several factors: the great variety of individual physical activity, inconsistency of study results or insufficient data. Furthermore, since there are no randomized prospective trials but only cohort and case control studies, any evidence is limited to level 2-3 (recommendation level „B“). A significant risk reduction was found for colon cancer (40-50 %), and estrogen dependent cancers such as breast (40-50 %) and endometrial cancer (35-40 %). Risk reduction is likely (ovarian and lung cancer) or possible (rectal, prostate, renal cell cancer and hematopoietic malignancies) for other neoplasias.
Plausible explanations for the cancer risk reduction have been investigated for colon and estrogen dependent cancers. The underlying molecular and biologic mechanisms of the beneficial exercise effects which are discussed in the literature include low estrogen levels, low expression of insulin-like growth factor (IGF) and prostaglandins. However, the exact mechanisms have not yet been elucidated comprehensively.
Only few studies reported on the time period in which increased physical exercise should be practiced to have a significant impact on the development of cancer. In humans, the process from cancer initiation to clinically detectable tumor growth is assumed to last years, if not decades. Therefore, the age-adjusted cancer incidence can be expected to be reduced by the effects of physical exercise, if physical exercise is practiced not only during the recent time period, but rather during the past several years or life-long.
Most studies investigating the level of physical exercise that is required to significantly decrease the risk of cancer report a dose dependent effect. At least four hours of moderate to vigorous physical activity per week are consistently reported to yield a maximum of cancer risk reduction. However, due to the study design, a standardized exercise program adapted to age and cofactors such as the cardiovascular risk profile cannot be derived.
Thus, the available data allow the recommendation of modification of the individual´s behaviour towards a “healthy life style” including four hours of physical exercise weekly which should be moderate or, preferentially, vigorous.
The review focuses on three topics of cancer risk reduction by physical exercise: i) the epidemiological data, ii) underlying molecular mechanisms, and iii) recommendations regarding the intensity of various activities. |
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