Physical inactivity increases the risk of cancer. While excessive exercise and overtraining may adversely impact treatment outcomes and quality of life, doing regular moderate exercises/physical activity may provide systemic beneficial effects such as improved physiological function, decreased risk of cancer incidence and recurrence, and better quality of life. Different studies have found beneficial impacts of regular moderate physical activities/exercise in cancers such as breast cancer, endometrial cancer and colorectal cancer. Based on genetic setup, one may also have to optimize the type of exercises that they should engage in, to reap maximum benefits.
Lack of physical activity has been shown as a primary risk factor for a variety of life threatening diseases such as cardiovascular diseases and cancer. In recent years, people have started recognizing the importance of physical activity in cancer patients and those who are at risk of cancers. Before we look into the scientific evidence which suggests the same, let us first refresh our understanding of the terms – Physical Activity, Exercise and Metabolic Equivalent of Task (MET).
Exercise and Physical Activity
Any voluntary movement of muscle resulting in energy expenditure may be broadly termed as physical activity. Unlike exercise, which is a form of physical activity that refers to the planned, repeated movements with the aim of staying healthy, physical activity is a more generalized term which may even include the general daily activities of our life such as performing household chores, transport, or a planned activity such as exercise or sports.
Some examples of different types of exercises include:
- Aerobic Exercises
- Resistance Exercises
Aerobic exercises are performed for improving the circulation of oxygen through the blood and are associated with increased rate of breathing and cardiorespiratory fitness. Some examples of aerobic exercises include brisk walking, jogging, cycling, rowing.
Resistance exercises are performed for improving muscular strength and endurance. Activities of this exercise cause muscles to contract against an external resistance, and are done via body weight (press ups, leg squats etc), resistance bands or machines, dumbbells or free weights.
Some of the exercises are a combination of both, such as climbing the stairs. Also, while some exercises are focused on improving flexibility such as mild stretching and Hatha yoga, some are focused on balance such as Yoga and Tai Chi.
Metabolic Equivalent of Task (MET)
Metabolic equivalent of task or MET, is a measure used to characterize the intensity of the physical activity. It is the rate at which a person expends energy, relative to the mass of that person, while performing some specific physical activity compared to a reference equivalent to the energy expended when sitting at rest. 1 MET is roughly the rate of energy expended by a person sitting at rest. Light physical activities expend less than 3 METs, moderate intensity activities expend 3 to 6 METs, and vigorous activities expend 6 or more METs.
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Importance of Physical Activity/Exercise in Cancer
Over the recent years, there is growing evidence suggesting that physical activity/exercise may have an impact on all stages of a cancer patient’s journey.
Scientific evidence supports that being physically active and doing regular exercises while undergoing cancer treatment as well as after the completion of the treatment may help in improving quality of life of cancer patients by controlling cancer related fatigue, improving cardiorespiratory and muscular fitness. Doing regular exercises by patients who are under palliative care may also help in controlling cancer related fatigue, maintaining physical function and improving bone health.
Association of Leisure-Time Physical Activity With Risk of 26 Types of Cancer
In a study published by JAMA Internal Medicine in 2016, Steven C. Moore of the National Cancer Institute, Bethesda and coauthors evaluated the self-reported physical activity data from 12 prospective U.S. and European cohorts from 1987 to 2004 inorder to understand the association between physical activity and the incidence of 26 different types of cancers. The study included a total of 1.4 million participants and 186,932 cancer cases. (Steven C Moore et al, JAMA Intern Med., 2016)
The study found that those with higher levels of physical activity compared to lower levels were associated with a reduced risk of 13 out of 26 cancers; with 42% reduced risk of esophageal adenocarcinoma, 27% reduced risk of liver cancer, 26% reduced risk of lung cancer, 23% reduced risk of kidney cancer, 22% reduced risk of gastric cardia cancer, 21% reduced risk of endometrial cancer, 20% reduced risk of myeloid leukemia, 17% reduced risk of myeloma, 16% reduced risk of colon cancer, 15% reduced risk of head and neck cancer, 13% reduced risk of rectal cancer, 13% reduced risk of bladder cancer and with 10% reduced risk of breast cancer. The associations remained the same regardless of factors such as body weight. Smoking status modified the association for lung cancer but not for other smoking-related cancers.
In short, leisure-time physical activity was associated with a reduced risk of 13 different types of cancers.
Association of Recreational Physical activity/Exercise with Mortality and Recurrence in Breast Cancer survivors
A study done by the researchers from the National and Kapodistrian University of Athens, Greece and University of Milan, Italy evaluated the association of physical activity after breast cancer diagnosis with all-cause mortality, breast cancer mortality and/or breast cancer recurrence. The analysis included 10 observational studies identified through Pubmed search until November 2017. During a mean follow-up of 3.5 to 12.7 years, a total of 23,041 breast cancer survivors, 2,522 deaths from all causes, 841 deaths from breast cancer and 1,398 recurrences were reported. (Maria-Eleni Spei et al, Breast., 2019)
The study found that compared to women with very low recreational physical activity, those women with high physical activity had a lower risk of deaths due to all causes, breast cancer and a lower risk of recurrence.
Association between Pre- and Post-diagnosis Physical Activity and Endometrial Cancer Survival
A prospective cohort study in Alberta, Canada, done by the researchers from the Alberta Health Services, University of Calgary and University of Alberta in Canada and the University of New Mexico, on 425 women who were diagnosed with endometrial cancer between 2002 and 2006 and observed till 2019, evaluated the association between pre- and post-diagnosis physical activity and survival in survivors of endometrial cancer. After a mean follow-up of 14.5 years, there were 60 deaths, including 18 endometrial cancer deaths, and 80 disease-free survival events. (Christine M Friedenreich et al, J Clin Oncol., 2020)
The study found that higher pre-diagnosis recreational physical activity was significantly associated with improved disease-free survival, but not overall survival; and higher post-diagnosis recreational physical activity was strongly associated with both improved disease-free survival and overall survival. Also, those who maintained high recreational physical activity levels from pre- to post-diagnosis had improved disease-free survival and overall survival compared with those who maintained very low physical activity levels.
Influence of a Structured Exercise Training on Quality of Life in Colorectal Cancer Patients
A study done by the researchers from different universities in Austria, called the ABCSG C07-EXERCISE study, evaluated the feasibility of a 1-year exercise training post adjuvant chemotherapy in colorectal cancer patients. These patients scored social functioning, emotional functioning, financial impact, insomnia, and diarrhea much worse than the German general population. (Gudrun Piringer et al, Integr Cancer Ther., Jan-Dec 2020)
The study found that after 1 year of a structured exercise training, there were large improvements reported for social functioning; moderate improvements reported for pain, diarrhea, financial impact, and taste; and a slight improvement for physical and emotional functioning as well as for global quality of life.
The researchers concluded that 1 year of structured exercise training in locally advanced colorectal cancer patients post adjuvant chemotherapy improved social, physical, and emotional functioning as well as global quality of life.
Are Long Hours of High Intensity Vigorous Exercises necessary for Cancer Patients or those at increased risk of cancers?
All the above studies definitely indicate that being physically active and doing regular exercises may reduce the risk of developing cancers, as well as improve survival and quality of life, reduce risk of deaths and recurrence in cancer patients and survivors. However, this does not mean that one needs to do very long hours of vigorous and highly intense exercise to reap these benefits. In fact, in many cases long hours of vigorous intense exercises may even do more harm than good. So in short, being physically inactive or doing long hours of vigorous intense exercise may not be beneficial.
One of the most common theories supporting this fact about the impact of physical activity/exercise on risk of cancer or outcomes in cancer patients is the hormesis theory.
Exercise and Hormesis
Hormesis is a process in which a biphasic response is observed when exposed to increasing amounts of a particular condition. During hormesis, a low dose of a chemical agent or an environmental factor that may be damaging at very high doses induces an adaptive beneficial effect on the organism.
While sedentary lifestyle and physical inactivity increases oxidative stress and excessive exercise and overtraining leads to damaging oxidative stress, moderate levels of regular exercise may help decrease the oxidative challenge to the body through adaptation. Cancer initiation and progression is associated with oxidative stress, as oxidative stress can increase DNA damage, genome variability, and cancer cell proliferation. Regular moderate exercise and physical activity may provide systemic beneficial effects such as improved physiological function, decreased risk of cancer and better quality of life.
Association between Physical Activity/Exercise and Risk of Digestive System Cancers
A recent meta-analysis done by the Shanghai University of Traditional Chinese Medicine, Naval Medical University in Shanghai and Shanghai University of Sport, China evaluated the effect of physical activity on different types of Digestive System Cancers based on 47 studies identified via literature search in online databases such as PubMed, Embase, Web of Science, Cochrane Library, and China National Knowledge Infrastructure. The study included a total of 5,797,768 participants and 55,162 cases. (Fangfang Xie et al, J Sport Health Sci., 2020)
The study found that compared to those with very low physical activity, people with high physical activity had a reduced risk of Digestive System Cancers, with 19% reduced risk of colon cancer, 12% reduced risk of rectal cancer, 23% reduced risk of colorectal cancer, 21% reduced risk of gallbladder cancer, 17% reduced risk of gastric cancer, 27% reduced risk of liver cancer, 21% reduced risk of oropharyngeal cancer, and 22% reduced risk of pancreatic cancer. These findings were true for both case-control studies and prospective cohort studies.
The meta-analysis of 9 studies which reported low, moderate, and high physical activity levels also found that compared to those with very low physical activity, moderate physical activity reduced the risk of Digestive System Cancers. However, interestingly, compared to those with moderate physical activity, high physical activity seemed to slightly increase the risk of developing Digestive System Cancers.
The findings suggest that while physical activity and doing regular exercises in moderate levels are important for reducing the risk of cancer, long hours of vigorous exercises may increase the risk of cancer.
Association between Physical activity/Exercise and Survival after breast cancer diagnosis
A study done by the researchers from the Brigham and Women’s Hospital and Harvard Medical School in Boston evaluated whether physical activity/exercise among women with breast cancer decreased their risk of death from breast cancer compared with more sedentary women. The study used data from the 2987 female registered nurses in the Nurses’ Health Study who were diagnosed with stage I, II, or III breast cancer between 1984 and 1998 and were followed up until death or June 2002. (Michelle D Holmes et al, JAMA., 2005)
The study found that compared with women who were engaged in less than 3 MET-hours (equivalent to walking at average pace of 2 to 2.9 mph for 1 hour) per week of physical activity/exercise, there was a 20% reduced risk of death from breast cancer for those who were engaged in 3 to 8.9 MET-hours per week; 50% reduced risk of death from breast cancer for those who were engaged in 9 to 14.9 MET-hours per week; 44% reduced risk of death from breast cancer for those who were engaged in 15 to 23.9 MET-hours per week; and 40% reduced risk of death from breast cancer for those who were engaged in 24 or more MET-hours per week, especially in women with hormone-responsive tumors.
The study indicated that physical activity/exercise after a breast cancer diagnosis may reduce the risk of death from this disease. The greatest benefit occurred in breast cancer women who performed the equivalent of walking 3 to 5 hours per week at an average pace and there was no increased benefit of more energy expenditure by doing more vigorous exercise.
Association between Physical activity and Risk of Endometrial Cancer
A study done by the researchers from the University of Washington School of Public Health and Fred Hutchinson Cancer Research Center in Washington and Brigham and Women’s Hospital and Harvard Medical School in Boston evaluated the association between physical activity and endometrial cancer. The study used data from 71,570 women in the Nurses’ Health Study. During a follow-up period from 1986 to 2008, 777 invasive endometrial cancers were reported. (Mengmeng Du et al, Int J Cancer., 2014)
Compared with <3 MET-hr/week (<1 hr/week walking), women engaged in moderate amounts of recent total recreational activity (9 to <18 MET-hr/week) had a 39% reduced risk of endometrial cancer and those engaged in high amounts of recent total recreational activity (≥27 MET-hr/week) had a 27% reduced risk of endometrial cancer.
Among women who did not perform any vigorous activity, recent walking was associated with 35% reduced risk (≥3 vs. <0.5 hr/week), and faster walking pace was independently associated with risk reduction. Greater recent physical activity, with activity of moderate duration and intensity such as walking, may reduce endometrial cancer risk. Those who were engaged in high amounts of recent total recreational activity had a slightly higher risk of endometrial cancer when compared to those engaged in moderate activities.
Different studies have found beneficial impacts of regular moderate physical activities/exercise in cancers such as breast cancer, endometrial cancer and digestive system cancers such as colorectal cancer. Many studies also suggested that while physical inactivity may increase the risk of cancer and excessive exercise and overtraining may adversely impact treatment outcomes and quality of life, regular moderate exercise and physical activity may provide systemic beneficial effects such as improved physiological function, decreased risk of cancer and better quality of life. Based on our genetic setup, we may also have to optimize the types of exercises we do to reap maximum benefits. Physical activity and exercises do play an important impact on all stages of a cancer patient’s journey.
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