Woods J A
Department of Kinesiology, University of Illinois at Urbana/Champaign 61801, USA.
Can J Physiol Pharmacol. 1998 May;76(5):581-8. doi: 10.1139/cjpp-76-5-581.
Epidemiological evidence has revealed an inverse relationship such that increased physical activity as measured directly subjective recall, job classification, former athletic status, or indirectly by physical fitness is associated with decreased incidence and (or) mortality rates for various cancers. The relationship appears strongest for colon cancer and female estrogen-dependent cancers of the breast, ovary, and endometrium. While some epidemiological studies have controlled for numerous confounding variables such as smoking, body mass index, and percent body fat, it is still difficult to ascertain whether physical activity exerts an independent effect on cancer above and beyond that associated with an improved lifestyle and numerous other potential confounding variables. Experimental studies performed in animals suggests that chronic exercise, especially when performed prior to tumorigenesis, can retard, delay, or prevent the incidence, progression, or spread of experimental tumors. There is also limited animal evidence suggesting that exercise may help ameliorate cancer cachexia. Exercise or physical activity may contribute to a reduction in site-specific cancers by different physiological mechanisms. Some purported mechanisms include decreased lifetime exposure to estrogen or other hormones, reduced body fat, enhanced gut motility, improved anti-oxidant defenses, and stimulation of anti-tumor immune defenses. Unfortunately, most animal studies have failed to account for plausible biological mechanisms as to how exercise might influence cancer. In addition, the exercise or activity dosage required to provide optimal protection from cancer is unclear. Interpretation of epidemiological studies is hampered by the numerous and sometimes inaccurate assessments of physical activity. Likewise, many animal studies have utilized unrealistic exercise protocols. Clearly, more research is needed to define appropriate activity or exercise dosages definitively and to explore the mechanism(s) by which exercise helps protect against cancer. Nevertheless, moderate exercise appears to be a safe and effective means of aiding in the prevention of cancer and should be adopted by the public in addition to other prudent behavioral practices such as proper diet. More research needs to be performed regarding the effects of exercise or physical activity on those who already have cancer to determine if exercise improves their prognosis.
流行病学证据显示了一种反向关系，即通过直接主观回忆、工作分类、既往运动状态直接测量的身体活动增加，或通过体能间接测量的身体活动增加，与各种癌症的发病率和（或）死亡率降低相关。这种关系在结肠癌以及女性雌激素依赖性的乳腺癌、卵巢癌和子宫内膜癌中似乎最为明显。虽然一些流行病学研究已经控制了许多混杂变量，如吸烟、体重指数和体脂百分比，但仍然难以确定身体活动是否在改善生活方式和众多其他潜在混杂变量之外，对癌症产生独立影响。在动物身上进行的实验研究表明，长期运动，尤其是在肿瘤发生之前进行运动，可以延缓、推迟或预防实验性肿瘤的发生、进展或扩散。也有有限的动物证据表明运动可能有助于改善癌症恶病质。运动或身体活动可能通过不同的生理机制有助于降低特定部位癌症的发生。一些所谓的机制包括减少一生中雌激素或其他激素的暴露、降低体脂、增强肠道蠕动、改善抗氧化防御以及刺激抗肿瘤免疫防御。不幸的是，大多数动物研究未能说明运动可能影响癌症的合理生物学机制。此外，提供最佳癌症防护所需的运动或活动剂量尚不清楚。流行病学研究的解读受到对身体活动的众多且有时不准确评估的阻碍。同样，许多动物研究采用了不切实际的运动方案。显然，需要更多的研究来明确确定适当的活动或运动剂量，并探索运动有助于预防癌症的机制。然而，适度运动似乎是辅助预防癌症的一种安全有效的方法，除了其他谨慎的行为习惯如合理饮食外，公众也应采用。关于运动或身体活动对已患癌症者的影响，还需要进行更多研究，以确定运动是否能改善他们的预后。
