Editor’s note: This is an article from NCI. It has been clear that physical exercise is extremely important for both cancer patients and healthy people. Evidence suggests that people who do moderate physical exercise are at reduced risk for cancer, and cancer patients who did not stop physical exercise after diagnosis are at better odds to survive.
編者註：這是NCI的文章。 很明顯，體育鍛煉對於癌症患者和健康人都極為重要。 有證據表明，進行中等程度的體育鍛煉的人患癌症的風險降低，而在診斷後未停止體育鍛煉的癌症患者生存的機率更高。
What is physical activity?
Physical activity is defined as any movement that uses skeletal muscles and requires more energy than resting. Physical activity can include walking, running, dancing, biking, swimming, performing household chores, exercising, and engaging in sports activities.
A measure called the metabolic equivalent of task, or MET, is used to characterize the intensity of physical activity. One MET is the rate of energy expended by a person sitting at rest. Light-intensity activities expend less than 3 METs, moderate-intensity activities expend 3 to 6 METs, and vigorous activities expend 6 or more METs (1).
Sedentary behavior is any waking behavior characterized by an energy expenditure of 1.5 or fewer METs while sitting, reclining, or lying down (1). Examples of sedentary behaviors include most office work, driving a vehicle, and sitting while watching television.
A person can be physically active and yet spend a substantial amount of time being sedentary.
What is known about the relationship between physical activity and cancer risk?
Evidence linking higher physical activity to lower cancer risk comes mainly from observational studies, in which individuals report on their physical activity and are followed for years for diagnoses of cancer. Although observational studies cannot prove a causal relationship, when studies in different populations have similar results and when a possible mechanism for a causal relationship exists, this provides evidence of a causal connection.
- Bladder cancer: In a 2014 meta-analysis of 11 cohort studies and 4 case-control studies, the risk of bladder cancer was 15% lower for individuals with the highest level of recreational or occupational physical activity than in those with the lowest level (5). A pooled analysis of over 1 million individuals found that leisure-time physical activity was linked to a 13% reduced risk of bladder cancer (6).
- Breast cancer: Many studies have shown that physically active women have a lower risk of breast cancer than inactive women. In a 2016 meta-analysis that included 38 cohort studies, the most physically active women had a 12–21% lower risk of breast cancer than those who were least physically active (7). Physical activity has been associated with similar reductions in risk of breast cancer among both premenopausal and postmenopausal women (7, 8). Women who increase their physical activity after menopause may also have a lower risk of breast cancer than women who do not (9, 10).
- Colon cancer: In a 2016 meta-analysis of 126 studies, individuals who engaged in the highest level of physical activity had a 19% lower risk of colon cancer than those who were the least physically active (11).
- Endometrial cancer: Several meta-analyses and cohort studies have examined the relationship between physical activity and the risk of endometrial cancer (cancer of the lining of the uterus) (12–15). In a meta-analysis of 33 studies, highly physically active women had a 20% lower risk of endometrial cancer than women with low levels of physical activity (12). There is some evidence that the association is indirect, in that physical activity would have to reduce obesity for the benefits to be observed. Obesity is a strong risk factor for endometrial cancer (12–14).
- Esophageal cancer: A 2014 meta-analysis of nine cohort and 15 case–control studies found that the individuals who were most physically active had a 21% lower risk of esophageal adenocarcinoma than those who were least physically active (16).
- Kidney (renal cell) cancer: In a 2013 meta-analysis of 11 cohort studies and 8 case–control studies, individuals who were the most physically active had a 12% lower risk of renal cancer than those who were the least active (17). A pooled analysis of over 1 million individuals found that leisure-time physical activity was linked to a 23% reduced risk of kidney cancer (6).
- Stomach (gastric) cancer: A 2016 meta-analysis of 10 cohort studies and 12 case–control studies reported that individuals who were the most physically active had a 19% lower risk of stomach cancer than those who were least active (18).
There is some evidence that physical activity is associated with a reduced risk of lung cancer (2, 4). However, it is possible that differences in smoking, rather than in physical activity, are what explain the association of physical activity with reduced risk of lung cancer. In a 2016 meta-analysis of 25 observational studies, physical activity was associated with reduced risk of lung cancer among former and current smokers but was not associated with risk of lung cancer among never smokers (19).
For several other cancers, there is more limited evidence of an association. These include certain cancers of the blood, as well as cancers of the pancreas, prostate, ovaries, thyroid, liver, and rectum (2, 6).
How might physical activity be linked to reduced risks of cancer?
Exercise has many biological effects on the body, some of which have been proposed to explain associations with specific cancers. These include:
- Lowering the levels of sex hormones, such as estrogen, and growth factors that have been associated with cancer development and progression (20) [breast, colon]
- Preventing high blood levels of insulin, which has been linked to cancer development and progression (20) [breast, colon]
- Reducing inflammation
- Improving immune system function
- Altering the metabolism of bile acids, decreasing exposure of the gastrointestinal tract to these suspected carcinogens (21, 22) [colon]
- Reducing the time it takes for food to travel through the digestive system, which decreases gastrointestinal tract exposure to possible carcinogens [colon]
- Helping to prevent obesity, which is a risk factor for many cancers
What is known about the relationship between being sedentary and the risk of cancer?
Although there are fewer studies of sedentary behavior and cancer risk than of physical activity and cancer risk, sedentary behavior—sitting, reclining, or lying down for extended periods of time (other than sleeping)—is a risk factor for developing many chronic conditions and premature death (4, 23, 24). It may also be associated with increased risk for certain cancers (23, 25).
How much physical activity is recommended?
The U.S. Department of Health and Human Services Physical Activity Guidelines for Americans, 2nd edition, released in 2018 (1), recommends that, for substantial health benefits and to reduce the risk of chronic diseases, including cancer, adults engage in
- 150 to 300 minutes of moderate-intensity aerobic activity, 75 to 100 minutes of vigorous aerobic activity, or an equivalent combination of each intensity each week. This physical activity can be done in episodes of any length.
- muscle-strengthening activities at least 2 days a week
- balance training, in addition to aerobic and muscle-strengthening activity
Is physical activity beneficial for cancer survivors?
Yes. A report of the 2018 American College of Sports Medicine International Multidisciplinary Roundtable on Physical Activity and Cancer Prevention and Control (26) concluded that exercise training and testing are generally safe for cancer survivors and that every survivor should maintain some level of physical activity.
The Roundtable also found
- strong evidence that moderate-intensity aerobic training and/or resistance exercise during and after cancer treatment can reduce anxiety, depressive symptoms, and fatigue and improve health-related quality of life and physical function
- strong evidence that exercise training is safe in persons who have or might develop breast-cancer-related lymphedema
- some evidence that exercise is beneficial for bone health and sleep quality
- insufficient evidence that physical activity can help prevent cardiotoxicity or chemotherapy-induced peripheral neuropathy or improve cognitive function, falls, nausea, pain, sexual function, or treatment tolerance
- Breast cancer: In a 2019 systematic review and meta-analysis of observational studies, breast cancer survivors who were the most physically active had a 42% lower risk of death from any cause and a 40% lower risk of death from breast cancer than those who were the least physically active (28).
- Colorectal cancer: Evidence from multiple epidemiologic studies suggests that physical activity after a colorectal cancer diagnosis is associated with a 30% lower risk of death from colorectal cancer and a 38% lower risk of death from any cause (4).
- Prostate cancer: Limited evidence from a few epidemiologic studies suggests that physical activity after a prostate cancer diagnosis is associated with a 33% lower risk of death from prostate cancer and a 45% lower risk of death from any cause (4).
What additional research is under way on the relationship between physical activity and cancer?
Findings from observational studies provide much evidence for a link between higher levels of physical activity and lower risk of cancer. However, these studies cannot fully rule out the possibility that active people have lower cancer risk because they engage in other healthy lifestyle behaviors. For this reason, clinical trials that randomly assign participants to exercise interventions provide the strongest evidence because they eliminate bias caused by pre-existing illness and attendant physical inactivity.
To confirm the observational evidence and define the potential magnitude of the effect, several large clinical trials are examining physical activity and/or exercise interventions in cancer patients and survivors. These include the Breast Cancer Weight Loss (BWEL) trial in newly diagnosed breast cancer patients, the CHALLENGE trial in colon cancer patients who have recently completed chemotherapy (29), and the INTERVAL-GAP4 trial in men with metastatic, castrate-resistant prostate cancer (30).
Many additional questions have yet to be answered in several broad areas of research on physical activity and cancer:
- What are the mechanisms by which physical activity reduces cancer risk?
- What is the optimal time in life, intensity, duration, and/or frequency of physical activity needed to reduce the risk of cancer, both overall and for specific sites?
- Is sedentary behavior associated with increased risk of cancer?
- Does the association between physical activity and cancer differ by age or race/ethnicity?
- Does physical activity reduce the risk of cancer in people who have inherited a genetic variant that increases cancer risk?
- 2018 Physical Activity Guidelines Advisory Committee. 2018 Physical Activity Guidelines Advisory Committee Scientific Report. Washington, DC: U.S. Department of Health and Human Services, 2018.
- McTiernan A, Friedenreich CM, Katzmarzyk PT, et al. Physical activity in cancer prevention and survival: A systematic review. Medicine and Science in Sports and Exercise 2019; 51(6):1252-1261. [PubMed Abstract]
- Rezende LFM, Sá TH, Markozannes G, et al. Physical activity and cancer: an umbrella review of the literature including 22 major anatomical sites and 770 000 cancer cases. British Journal of Sports Medicine 2018; 52(13):826-833. [PubMed Abstract]
- Patel AV, Friedenreich CM, Moore SC, et al. American College of Sports Medicine Roundtable Report on physical activity, sedentary behavior, and cancer prevention and control. Medicine and Science in Sports and Exercise 2019; 51(11):2391-2402. [PubMed Abstract]
- Keimling M, Behrens G, Schmid D, Jochem C, Leitzmann MF. The association between physical activity and bladder cancer: systematic review and meta-analysis. British Journal of Cancer 2014; 110(7):1862-1870. [PubMed Abstract]
- Moore SC, Lee IM, Weiderpass E, et al. Association of leisure-time physical activity with risk of 26 types of cancer in 1.44 million adults. JAMA Internal Medicine 2016; 176(6):816-825. [PubMed Abstract]
- Pizot C, Boniol M, Mullie P, et al. Physical activity, hormone replacement therapy and breast cancer risk: A meta-analysis of prospective studies. European Journal of Cancer 2016; 52:138-154. [PubMed Abstract]
- Hardefeldt PJ, Penninkilampi R, Edirimanne S, Eslick GD. Physical activity and weight loss reduce the risk of breast cancer: A meta-analysis of 139 prospective and retrospective studies. Clinical Breast Cancer 2018; 18(4):e601-e612. [PubMed Abstract]
- Eliassen AH, Hankinson SE, Rosner B, Holmes MD, Willett WC. Physical activity and risk of breast cancer among postmenopausal women. Archives of Internal Medicine 2010; 170(19):1758-1764. [PubMed Abstract]
- Fournier A, Dos Santos G, Guillas G, et al. Recent recreational physical activity and breast cancer risk in postmenopausal women in the E3N cohort. Cancer Epidemiology, Biomarkers & Prevention 2014; 23(9):1893-1902. [PubMed Abstract]
- Liu L, Shi Y, Li T, et al. Leisure time physical activity and cancer risk: evaluation of the WHO’s recommendation based on 126 high-quality epidemiological studies. British Journal of Sports Medicine 2016; 50(6):372-378. [PubMed Abstract]
- Schmid D, Behrens G, Keimling M, et al. A systematic review and meta-analysis of physical activity and endometrial cancer risk. European Journal of Epidemiology 2015; 30(5):397-412. [PubMed Abstract]
- Du M, Kraft P, Eliassen AH, et al. Physical activity and risk of endometrial adenocarcinoma in the Nurses’ Health Study. International Journal of Cancer 2014; 134(11):2707-2716. [PubMed Abstract]
- Friedenreich C, Cust A, Lahmann PH, et al. Physical activity and risk of endometrial cancer: The European prospective investigation into cancer and nutrition. International Journal of Cancer 2007; 121(2):347-355. [PubMed Abstract]
- Borch KB, Weiderpass E, Braaten T, et al. Physical activity and risk of endometrial cancer in the Norwegian Women and Cancer (NOWAC) study. International Journal of Cancer 2017; 140(8):1809-1818. [PubMed Abstract]
- Behrens G, Jochem C, Keimling M, et al. The association between physical activity and gastroesophageal cancer: systematic review and meta-analysis. European Journal of Epidemiology 2014; 29(3):151-170. [PubMed Abstract]
- Behrens G, Leitzmann MF. The association between physical activity and renal cancer: systematic review and meta-analysis. British Journal of Cancer 2013; 108(4):798-811. [PubMed Abstract]
- Psaltopoulou T, Ntanasis-Stathopoulos I, Tzanninis IG, et al. Physical activity and gastric cancer risk: A systematic review and meta-analysis. Clinical Journal of Sports Medicine 2016; 26(6):445-464. [PubMed Abstract]
- Schmid D, Ricci C, Behrens G, Leitzmann MF. Does smoking influence the physical activity and lung cancer relation? A systematic review and meta-analysis. European Journal of Epidemiology 2016; 31(12):1173-1190. [PubMed Abstract]
- Winzer BM, Whiteman DC, Reeves MM, Paratz JD. Physical activity and cancer prevention: a systematic review of clinical trials. Cancer Causes and Control 2011; 22(6):811-826. [PubMed Abstract]
- Wertheim BC, Martinez ME, Ashbeck EL, et al. Physical activity as a determinant of fecal bile acid levels. Cancer Epidemiology, Biomarkers & Prevention 2009; 18(5):1591-1598. [PubMed Abstract]
- Bernstein H, Bernstein C, Payne CM, Dvorakova K, Garewal H. Bile acids as carcinogens in human gastrointestinal cancers. Mutation Research 2005; 589(1):47-65. [PubMed Abstract]
- Schmid D, Leitzmann MF. Association between physical activity and mortality among breast cancer and colorectal cancer survivors: a systematic review and meta-analysis. Annals of Oncology 2014; 25(7):1293-1311. [PubMed Abstract]
- Biswas A, Oh PI, Faulkner GE, et al. Sedentary time and its association with risk for disease incidence, mortality, and hospitalization in adults: a systematic review and meta-analysis. Annals of Internal Medicine 2015; 162(2):123-132. [PubMed Abstract]
- Patel AV, Hildebrand JS, Campbell PT, et al. Leisure-time spent sitting and site-specific cancer incidence in a large U.S. cohort. Cancer Epidemiology, Biomarkers & Prevention 2015; 24(9):1350-1359. [PubMed Abstract]
- Campbell KL, Winters-Stone KM, Wiskemann J, et al. Exercise guidelines for cancer survivors: Consensus statement from International Multidisciplinary Roundtable. Medicine and Science in Sports and Exercise 2019; 51(11):2375-2390. [PubMed Abstract]
- Schmitz KH, Campbell AM, Stuiver MM, et al. Exercise is medicine in oncology: Engaging clinicians to help patients move through cancer. CA: A Cancer Journal for Clinicians 2019; 69(6):468-484. [PubMed Abstract]
- Spei ME, Samoli E, Bravi F, et al. Physical activity in breast cancer survivors: A systematic review and meta-analysis on overall and breast cancer survival. Breast 2019; 44:144-152. [PubMed Abstract]
- Courneya KS, Booth CM, Gill S, et al. Curr Oncol. The Colon Health and Life-Long Exercise Change trial: a randomized trial of the National Cancer Institute of Canada Clinical Trials Group. Current Oncology 2008; 15(6):279-285. [PubMed Abstract]
- Newton RU, Kenfield SA, Hart NH, et al. Intense exercise for survival among men with metastatic castrate-resistant prostate cancer (INTERVAL-GAP4): a multicentre, randomised, controlled phase III study protocol. BMJ Open 2018; 8(5):e022899. [PubMed Abstract]