Proven Health Benefits Of Exercise In Preventing Cancer

Do you know that the global population is getting fatter? Being overweight (BMI over 25) or obese (BMI over 30) is the biggest cause of cancer after smoking, according to Cancer Research UK. Overweight/obesity accounts for 40% of all cancers in the United States according to the Centers For Disease Control (CDC). Overweight women are at higher risk for breast cancer because extra fat cells make estrogen, which, in turn, can cause extra breast cell growth.^1,2 The location of the extra weight matters; extra fat around your stomach may increase risk more than the same amount of extra fat around your thighs or hips.² 

Being significantly overweight and inactive produces dramatic hormonal and metabolic changes that create the optimum environment for the onset and proliferation of cancer cells. Exercise, by speeding up metabolism, is generally believed to speed up the passage of ingested foods through the colon — thus reducing the amount of time the colon mucosal lining is in contact with possible carcinogens³.

Exercise has many proven health benefits for preventing disease and promoting health and well-being. There is substantial evidence that suggests that increasing physical activity, including structured exercise programs, is associated with lower rates of certain cancers.⁴  In one study from the Women's Health Initiative, as little as 1.25 to 2.5 hours per week of brisk walking reduced a woman's breast cancer risk by 18%⁵. Cancers of the colon, prostate, lung, and uterus have also been linked to exercise-related prevention. 

Evidence From Harvard Alumni

In a large-scale study of 17,148 Harvard alumni, men who burned as few as 500 calories a week in exercise - the equivalent of an hour's worth of brisk walking or less than ten minutes of walking a day - had death rates 15-20 percent lower than men who were almost completely sedentary.^3,4 

Men who burned 2,000 calories a week (about four hours of brisk walking per week) had about 35 per cent lower cancer mortality. The researchers concluded that the more exercise you get, the lower your risk of premature death from cancer or heart disease.^{6, 7} The Harvard study also found that the risk of colon cancer, the second leading cause of cancer-related death in the U.S., was dramatically reduced by exercise.^{6, 7} Prostate cancer is the most common cancer affecting men today.^{6, 7, 8} In the Harvard study, alumni who expended greater than 4,000 calories per week (equivalent to about eight hours of brisk walking) were at a reduced risk of developing prostate cancer compared to their inactive counterparts. ^{6, 7}

According to the American Cancer Society, for the great majority of Americans who do not smoke cigarettes, dietary choices and physical activity are the most important modifiable determinants of cancer risk.⁴ Evidence suggests that one-third of the more than 500,000 cancer deaths that occur in the United States each year can be attributed to diet and physical activity habits, with another third due to cigarette smoking.^{6, 7}

Evidence From The National Cancer Institute (NCI)

A new study of the relationship between physical activity and cancer has shown that greater levels of leisure-time physical activity were associated with a lower risk of developing 13 different types of cancer.^{6, 9} The risk of developing seven cancer types was 20 per cent (or more) lower among the most active participants (90th percentile of activity) as compared with the least active participants (10th percentile of activity).^{6, 9} These findings, from researchers at the NCI, part of the National Institutes of Health, and the American Cancer Society, confirm and extend the evidence for the benefit of physical activity on cancer risk and support its role as a key component of population-wide cancer prevention and control efforts. 

This new study pooled data on 1.44 million people, ages 19 to 98, from the United States and Europe, and examined a broad range of cancers, including rare malignancies.^10,11  Participants were followed for a median of 11 years, during which 187,000 new cancer cases occurred.^10,11

The investigators confirmed that leisure-time physical activity, as assessed by self-reported surveys, was associated with a lower risk of colon, breast, and endometrial cancers.^10,11  They also determined that leisure-time physical activity was associated with a lower risk of 10 additional cancers, with the greatest risk reductions for esophageal adenocarcinoma, liver cancer, cancer of the gastric cardia, kidney cancer, and myeloid leukemia.^10,11  Myeloma and cancers of the head and neck, rectum, and bladder also showed reduced risks that were significant, but not as strong.^10,11  Risk was reduced for lung cancer, but only for current and former smokers; the reasons for this are still being studied.^10,11  Leisure-time physical activity is defined as exercise done at one's discretion, often to improve or maintain fitness or health. Examples include walking, running, swimming, and other moderate to vigorous-intensity activities. The median level of activity in the study was about 150 minutes of moderate-intensity activity per week, which is comparable to the current recommended minimum level of physical activity for the U.S. population.^10,11

There are several mechanisms through which physical activity could affect cancer risk.¹²  It has been hypothesised that cancer growth could be initiated or abetted by three metabolic pathways also affected by exercise: sex steroids (estrogens and androgens); insulin and insulin-like growth factors; and proteins involved with both insulin metabolism and inflammation.¹²  Additionally, several non-hormonal mechanisms have been hypothesised to link physical activity to cancer risk, including inflammation, immune function, oxidative stress, and, for colon cancer, a reduction in the time that it takes for waste to pass through the gastrointestinal tract.¹²  Those who engage in a high level of physical activity are much less likely to smoke cigarettes, the single largest contributor to cancer.¹¹

It is not clear exactly how high amounts of physical activity work to prevent cancer. We know that exercise can help prevent obesity, which is related to some types of cancers.¹¹  Exercise burns calories, regulates metabolism, relieves stress and may reduce the urge to eat. Learning to control our response to life’s stresses may play a major role in weight maintenance and uncontrolled cravings and binging. Achieving and maintaining a healthy body weight is an essential component of cancer prevention and treatment. A carefully planned program of gradual weight reduction, focusing on healthy eating and exercising, is a strong step in the direction to help protect against cancer and assist in its treatment.

References:

1. AICR's Cancer Research Update. Obesity and Diabetes Responsible for Rising Global Cancer Burden. J Pathol. 2018 Apr;244(5):667-676. doi: 10.1002/path.5047. Epub 2018 Mar 12. The microbiome of cancer. AICR's Cancer Research Update. Feb 7, 2018
2. Kathy D Miller, Jessica L Sollars, Sandra K Althouse, Linda K Han, Stephen J Ventura, and Jeffrey S Sledge. Abstract P1-09-01: Beyond fatigue – The impact of breast cancer treatment on body composition and energy expenditure. Cancer Res May 1, 2015 75:P1-09-01; doi:10.1158/1538-7445.SABCS14-P1-09-01
3. National Cancer Institute, Genetic Testing for Inherited Cancer Susceptibility Syndromes
4. Laura Stefani, Giorgio Galanti, and Riggs Klika, Clinical Implementation of Exercise Guidelines for Cancer Patients: Adaptation of ACSM’s Guidelines to the Italian Model, 6 November 2016; Accepted: 30 December 2016; Published: 13 January 2017
5. McTiernan A, Kooperberg C, White E, Wilcox S, Coates R, Adams-Campbell LL, Woods N, Ockene J; Women's Health Initiative Cohort Study. Recreational physical activity and the risk of breast cancer in postmenopausal women: the Women's Health Initiative Cohort Study, JAMA, Sept. 10, 2003
6. Mayo Clinic. Mayo Clinic Cancer Center - Research
7. Halverstadt and Leonard, Essential Exercises for Breast Cancer Survivors. Harvard Common Press, Boston, MA, 2000
8. Hyuna Sung PhD, Jacques Ferlay MSc, ME, Rebecca L. Siegel MPH, Mathieu Laversanne MSc, Isabelle Soerjomataram MD, MSc, PhD, Ahmedin Jemal DMV, PhD, Freddie Bray BSc, MSc, PhD; Global Cancer Statistics 2020: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. First published: 04 February 2021
9. World Cancer Research Fund; American Institute for Cancer Research (2007). Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective (PDF). Washington, D.C.: American Institute for Cancer Research. ISBN 978-0-9722522-2-5. Archived from the original (PDF) on 25 March 2009
10. American Cancer Society, Almost 4% of Cancers Worldwide Due to Excess Body Weight, Dec. 19, 2018
11. National Cancer Institute, Obesity and Cancer
12. World Cancer Research Fund/American Institute for Cancer Research, How diet, nutrition, and physical activity affect kidney cancer risk