Everyone knows they’re supposed to exercise. But what type of exercise is best? How long should we do it? How many days a week? Strength training? Flexibility? What about cardio?
While the questions around exercise are confusing for any person, they can be exponentially more so for someone who fears, has faced or is facing a cancer diagnosis.
Research into the benefits of exercise for cancer prevention and oncology patients has typically focused on specific cancers and has largely been piecemeal. So, in 2018, the American College of Sports Medicine (ACSM) convened an International Multidisciplinary Roundtable on Exercise and Cancer to evaluate and translate the evidence linking physical activity and cancer prevention, treatment and control. You can find their report here and key findings are summarized below.
The Biology of Cancer and Exercise
There are more than 100 different types of cancer, the report acknowledges and, “Cancer development is a multistep process.” During this process, both exogenous (outside the body) and endogenous (inside the body) factors can affect the growth and development of transformed cells, leading to malignancy and progression.
“Physical activity,” the report explains, “is believed to affect the endogenous systemic milieu in a manner that influences cellular processes and tumor growth,” and science has explored many of these possibilities. Some of these include the role of insulin and glucose metabolism, inflammation, immune functioning, sex hormones, oxidative stress, genomic instability and myokines.
The Roundtable Report finds that “Preclinical animal studies have shown that physical activity can slow tumor growth across a wide range of cancer types.” The impacts vary from a reduction in cell proliferation to activation of tumor suppressive genes to effects on tumor blood vessels.
Additionally, some of the same mechanisms are being investigated for their potential impacts on tumor metastasis. These include changes in “adiposity, metabolic dysregulation, increasing circulating concentrations of adipokines and sex hormones, chronic low-grade inflammation, oxidative stress causing DNA damage with resulting gene mutations, and impaired immune surveillance and function.” Some studies even suggest exercise may improve the impact of treatment for cancer.
Exercise & Cancer Prevention
At a previous ACSM roundtable, convened in 2008, “there was only strong evidence linking physical activity with reduced risk of developing breast and colon cancer, and limited evidence linking physical activity with reduced risk of developing five other cancers.” You can find a table of that data in the report.
A decade later, armed with more evidence, there is strong evidence of that physical activity lowers the risk of: colon, breast, endometrium, bladder, liver and stomach cancer as well as esophageal adenocarcinoma. Plus, there is moderate evidence for a lowered risk for lung cancer.
The report did note an increased risk with one type of cancer, melanoma, and urged sun safety for all outdoor exercise.
Exercise & Cancer Survival
“At the time of the Roundtable at least 61 observational studies, involving breast, colorectal, prostate, endometrium, ovarian, kidney, lung, melanoma, lymphoma, childhood, esophageal, gastric, and malignant glioma cancer, had examined the association between the amount of physical activity and cancer survival …” and a table of findings is available in the report.
Notable findings include:
“The highest level of physical activity prediagnosis was associated with an 18% lower breast cancer mortality risk (HR = 0.82) and 23% lower colorectal cancer mortality risk (HR = 0.77).”
“Risk of all-cause mortality, as assessed in 17 breast, 7 colorectal and 2 prostate cancer cohort studies, was significantly lower and ranged between 13% lower for prostate cancer and 25% lower for colorectal cancer when comparing the highest versus the lowest level of prediagnosis physical activity.”
“A consistent inverse association with all-cause mortality was also found for breast (n = 13 studies), colorectal (n = 9 studies), and prostate cancer (n = 3 studies), with 21% to 45% lower mortality risk.”
“Taking into account the strength of associations observed for breast, colorectal, and prostate cancer, the evidence suggests that postdiagnosis physical activity exerts greater effects on mortality outcomes, compared with prediagnosis physical activity.”
For breast cancer, “15% of studies examining prediagnosis physical activity and 71% of studies examining postdiagnosis physical activity found evidence for a linear relationship between physical activity levels and cancer-specific mortality outcomes.”
These findings suggest that, for many cancers, a lack of a prediagnosis exercise regimen should not deter oncology patients from exercising postdiagnosis. As always, consult with your healthcare provider before beginning an exercise program.
But What Should I Actually Be Doing?
The report lays out some of the complications in analyzing data on what type of exercise is ideal and how much is enough. There exists a, “wide range of methods used for physical activity assessments and activity classification … used in individual studies.” Accordingly, it is “not possible to determine the amount of leisure time physical activity associated with lower risk of cancer, or to characterize the shape of the dose-response curve reliably.”
Which leaves us exactly where we began … what (and how much) exercise should I actually be doing?
How Long?
The report concludes that the evidence supports the current ACSM guidelines for the general population: 150 to 300 minutes per week of moderate activity, or an equivalent amount of vigorous intensity aerobic activity.
How Hard?
“The best available evidence from studies of leisure time physical activity,” the report states, “indicates that moderate to vigorous physical activity is associated with reduced risk of many types of cancer.”
What Type?
The report did not explore varying exercise modalities in any detail beyond the ACSM guidelines.
In Conclusion
While there is ample room for more study, “strong evidence exists to support an association between physical activity and cancer risk and survival for many types of cancer.”
To learn more about exercise and cancer, visit the ACSM website here.
As always, please consult your healthcare provider before beginning an exercise program.