Prominent scientific literature shows promising evidence that higher physical activity levels might lower the risk of 13 types of cancers. I explain the key mechanisms behind the reasons.

This story does not include health advice. It is for information, inspiration, and awareness purposes.

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In 2016, my wife returned from the funeral of her closest friend, who was taken by colon cancer at just 47. While she was sharing the emotions of the sad occasion, the TV in our living room suddenly caught our attention:

“By the time you hit midlife, odds are you or someone close to you will be touched by cancer. Cancer remains a potentially lethal lottery, and everyone’s experience is different. But appropriate exercise under professional supervision — before, during, or after treatment — seems to improve your odds substantially.”

We stopped discussing her challenging day and completed watching this half-hour documentary showing the insights of oncologists and sports medicine experts empowering cancer patients.

Discussing cancer has always been a challenge to me, as it is a subject close to my heart. The loss of relatives, friends, and colleagues over the past fifty years has made me acutely aware of the need to understand the ongoing research and apply the findings to protect myself and those I care about.

In the same year (2016), when my wife’s best friend died, JAMA Internal Medicine investigated the association of leisure-time physical activity with the risk of 26 types of cancer in 1.44 million adults. Researchers concluded that leisure-time physical activity was associated with lower risks of 13 cancer types.

Seven years later, in October 2023, researchers published in Nature based on their extensive reviews informed us that regular physical activity is associated with lower cancer incidence and mortality and a lower tumor recurrence rate. The epidemiological evidence is supported by preclinical studies in animal models showing that regular exercise delays the progression of cancer, including highly aggressive malignancies.

Like these researchers, my intense reviews indicate that “Exercise stimulates different immune cell subtypes to infiltrate tumors. There is also evidence that immune cells from blood collected after an exercise bout could be used as adoptive cell therapy for cancer.”

After extensively investigating the literature, I felt compelled to condense my findings into a digestible piece to ensure this information reaches many readers. I organized this story into two sections: outlining the types of cancers that benefit from physical activity and explaining the mechanisms through five overarching categories, addressing known factors that contribute to the development or worsening of the diseases.

As a seasoned researcher and educator, I see it as my duty to share my findings, contribute to spreading knowledge, and advocate for public health initiatives. Scientific literature provides strong evidence that higher levels of physical activity are linked to lower risk of several types of cancer.

While cancer is fundamentally a genetic disorder, emerging research emphasizes the influence of lifestyle and environmental factors on its development. In response, there have been concerted efforts by scientists, clinicians, and regulatory bodies to address this multifaceted challenge and educate the public.

All lifestyle factors play a role in mitigating cancer risks. However, this story centers only on the impact of physical exercise. My motivation for writing this piece stems from inquiries by new readers who sought a simplified explanation of the mechanisms underlying the beneficial effects of physical activity in preventing cancer.

Sedentary behavior, characterized by prolonged sitting, reclining, or lying down (excluding sleep), is recognized as a risk factor for various chronic conditions and premature mortality. While research on the link between sedentary behavior and cancer risk is less extensive compared to that of physical activity, evidence suggests that prolonged sedentary behavior may elevate the risk for certain cancers.

Evidence-Based Insights for the Beneficial Impact of Physical Exercise on 6 Types of Cancer

This 2019 study, conducted until December 2016 and updated research until February 2018, was reviewed as a generic meta-analysis and systemic review. The analysis encompassed numerous epidemiologic studies involving millions of participants. Strong evidence was found linking higher physical activity levels to reduced risks of bladder, breast, colon, endometrial, esophageal adenocarcinoma, and renal and gastric cancers, with risk reductions ranging from approximately 10% to 20%.

1 — Breast Cancer

This 2019 meta-analysis of 38 cohort studies in 45 study reports investigated physical activity and the risk of breast cancer. They found that the most physically active women experienced a 12–21% decrease in breast cancer risk compared to the least active individuals. This risk reduction is observed in both premenopausal and postmenopausal women.

This 2014 study examined the link between body measurements, physical activity, and breast cancer risk in women from the Canadian Study of Diet, Lifestyle, and Health with a subcohort of 3,320 women from a larger group of 39,532 participants who completed lifestyle and dietary questionnaires. They found that adult weight gain was associated with a higher risk of post-menopausal breast cancer, with a 6% increase for every 5 kg gained since age 20.

Women who exercised more than 30.9 MET hours per week had a 21% lower risk of breast cancer compared to those who exercised less than 3 MET hours per week, particularly among pre-menopausal women.

2 — Bladder Cancer

This 2014 meta-analysis in Nature included 15 studies involving 5,402,369 subjects and 27,784 cases of bladder cancer. High levels of physical activity were linked to a reduced risk of bladder cancer (summary relative risk (RR) = 0.85, 95% confidence interval (CI) = 0.74–0.98).

This association was consistent across cohort and case-control studies, as well as for both men and women. Recreational and occupational physical activity, as did the moderate and vigorous activity, showed similar risk reductions.

JAMA researchers in 2016 produced similar findings on bladder cancer. A pooled analysis of over 1 million individuals found that leisure-time physical activity was linked to a 13% reduced risk of bladder cancer.

3 — Colorectal (Colon) Cancer

This 2016 meta-analysis in the British Journal of Sports Medicine included 126 high-quality studies, revealing that individuals engaging in the highest levels of leisure-time physical activity had a 10% reduced risk of total cancer compared to those with the lowest activity levels.

Dose-response analysis showed that meeting the current WHO recommendation (equivalent to an average of 10 metabolic equivalents of energy hours per week) led to a 7% reduction in cancer risk.

However, the protective effect of exercise plateaued at 20 metabolic equivalents of energy hours per week, with a relative risk of 0.91. Subanalyses by cancer type found significant protection from breast and colorectal cancer (19% lower risk) associated with leisure-time physical activity.

4 — Gastrointestinal Cancers (Esophageal & Stomach Cancer)

This 2014 meta-analysis analyzed 24 studies with 15,745 cases to understand the link between physical activity levels and gastrointestinal cancers. They found that high physical activity levels were associated with lower risks of esophageal adenocarcinoma, gastric cardia adenocarcinoma, and gastric non-cardia adenocarcinoma.

They concluded that engaging in moderate to vigorous physical activity five times per week had the greatest risk reduction for total gastroesophageal cancer. Their findings suggest that physical activity, especially regular exercise, may lower the risk of gastroesophageal cancers.

This 2016 meta-analysis in the Clinical Journal of Sports Medicine included ten cohort studies with 7,551 incident cases among 1,541,208 subjects and 12 case-control studies with 5,803 cases and 73,629 controls. They found that engaging in “any” type of physical activity was linked to a lower risk of gastric cancer, with a pooled relative risk (RR) of 0.81 and a 95% confidence interval (CI) of 0.73 to 0.89.

5 — Renal Cell (Kidney) Cancer

This 2013 meta-analysis in Nature’s British Journal of Cancer reviewed studies on physical activity and kidney cancer risk in people without a history of cancer. Following PRISMA guidelines, they reviewed 19 studies involving 2,327,322 subjects and 10,756 cases.

Their analysis found that higher physical activity levels were associated with a lower risk of kidney cancer. Their meta-analysis's summary relative risk was 0.88, with a 95% confidence. When they focused on high-quality studies, the association was even stronger. They found no differences based on factors like obesity, hypertension, diabetes, smoking, gender, or location.

In conclusion, their thorough meta-analysis supports the link between physical activity and a reduced risk of kidney cancer. However, further research is needed to understand which specific types, intensities, frequencies, and durations of physical activity are most effective for lowering this risk.

6 — Endometrial Cancer

Endometrial cancer originates in the lining of the uterus. It is the most common cancer of the female reproductive system. Several meta-analyses and cohort studies have examined the relationship between physical activity and the risk of endometrial cancer.

For example, this 2015 systematic review and meta-analysis analyzed 33 studies up to October 2014, covering 19,558 cases of endometrial cancer.

High physical activity levels were associated with a reduced risk of endometrial cancer (RR=0.80; 95% CI 0.75–0.85). Recreational, occupational, and walking activities were all associated with lower risk, with walking for transportation showing the strongest effect.

Light, moderate, and vigorous activities showed inverse associations with cancer risk. Postmenopausal women also benefited from physical activity, but not premenopausal women. Overweight or obese women particularly benefitted from physical activity.

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. Numerous unanswered questions remain across various research domains concerning physical activity and cancer.

We still don’t know the exact and specific mechanisms underlying the risk-reducing effects of physical activity on cancer.

We still need to learn about the ideal timing, intensity, duration, and frequency of physical activity to mitigate cancer risk, both for overall prevention and at specific sites.

We are not sure if prolonged sedentary behavior is linked to heightened cancer risk and unsure about whether there are age or race/ethnicity disparities in the relationship between physical activity and cancer risk.

Current research is focusing on whether engaging in physical activity diminishes cancer risk among individuals with inherited genetic predispositions to cancer. Based on my research, I’d like to summarize what we know so far based on the hypotheses of various studies.

1- Making the Body More Insulin Sensitive and Preventing Obesity

Enhancing insulin sensitivity and combatting obesity are crucial strategies in cancer prevention. Cancer cells thrive in environments rich in sugar, and obesity exacerbates cancer risks due to metabolic dysfunctions. By preventing obesity, a recognized risk factor for various cancers, and mitigating elevated insulin levels in the blood, we can reduce the likelihood of cancer development and progression, particularly concerning breast and colon cancer.

2 — Improving the Immune System

Regular physical activity exerts its cancer-preventive effects through several immune mechanisms. It can enhance immune function by boosting the activity of immune cells, facilitating better surveillance and elimination of abnormal cells like cancer cells. Exercise can stimulate DNA repair mechanisms within cells, mitigating the accumulation of DNA damage and reducing the risk of mutations that could lead to cancer.

3 — Lowering Oxidative Stress and Inflammation

Regular exercise can reduce oxidative stress and inflammation, which are implicated in cancer development. By promoting the release of anti-inflammatory molecules and decreasing the production of pro-inflammatory substances, exercise can regulate chronic inflammation and create an environment less conducive to cancer growth.

4 — Optimizing Sex Hormones

Regular physical activity contributes to reducing the levels of sex hormones and growth factors linked to cancer development and progression, particularly in breast and colon cancers. By influencing hormone levels, including insulin and estrogen, exercise diminishes the stimulatory effects of these hormones on cancer cells.

5 — Improving Digestive Health

Regular physical activity positively impacts digestive health by altering the metabolism of bile acids, thereby reducing the gastrointestinal tract’s exposure to potential carcinogens, particularly colon cancer. Additionally, exercise can accelerate the transit time of food through the digestive system, further minimizing the contact of the gastrointestinal tract with potential carcinogens.

Summary of what is known about the relationship between physical activity and 13 types of cancer risks

As documented by NIH in 2016, “Hundreds of previous studies have examined associations between physical activity and cancer risk and shown reduced risks for colon, breast, and endometrial cancers; however, results have been inconclusive for most cancer types due to small numbers of participants in the studies.”

The study, published in JAMA Internal Medicine in 2016, analyzed data from 1.44 million people aged 19 to 98 in the US and Europe for 26 types of cancers. Results indicate that people with greater physical activity levels had a notably lower risk of developing 13 types of cancer, with a 20% or higher risk reduction observed for seven cancer types.

The study showed the benefits of physical activity on 13 cancers, including Breast, Colon, Endometrial, Ovarian, Prostate, Lung, Kidney, Bladder, Liver, Stomach, Thyroid, Skin, and Pancreatic Cancer. The most common mechanisms of physical activity were hormone regulation, insulin sensitivity, enhanced immune function, reduction of inflammation, lowered stress, improved metabolic health, and weight management.

Is physical activity beneficial for cancer survivors?

As the National Cancer Institute documented, Physical activity holds significant benefits for cancer survivors, as highlighted by the 2018 American College of Sports Medicine International Multidisciplinary Roundtable on Physical Activity and Cancer Prevention and Control.

The report highlights that exercise training is generally safe for survivors and emphasizes maintaining physical activity levels. Strong evidence suggests that moderate-intensity aerobic training and/or resistance exercise during and after cancer treatment can reduce anxiety, depression, and fatigue while improving quality of life and physical function.

Exercise is considered safe for people with or at risk of breast cancer-related lymphedema. Although evidence supports exercise’s positive impact on bone health and sleep quality, its effects on preventing cardiotoxicity, neuropathy, cognitive function, and other aspects remain inconclusive.

How much physical activity do we need to lower the risks of cancer?

There is a massive debate in fitness communities about the amount of physical activity. However, I personally use the 779-page guidelines (publicly available) from the U.S. Department of Health and Human Services Physical Activity Guidelines for Americans.

This guide informs that to reduce the risk of chronic diseases, including cancer, people need to aim to engage in 150 to 300 minutes of moderate-intensity aerobic activity, 75 to 100 minutes of vigorous aerobic activity, or an equivalent combination of both intensities each week.

This physical activity can be accumulated in episodes of any length throughout the week. Additionally, the guidelines recommend incorporating muscle-strengthening activities at least two days a week, balance training, and aerobic and muscle-strengthening exercises.

Conclusions and Takeaways

The evidence linking higher physical activity to lower cancer risk primarily stems from observational studies, wherein individuals self-report their physical activity levels and are monitored over the years for cancer diagnoses. While observational studies cannot definitively establish causation, consistent findings across diverse populations and the existence of potential mechanisms supporting a causal relationship lend support to such a connection.

According to comprehensive JAMA research, leisure-time physical activities are at an individual’s discretion to improve or maintain fitness or health. Their analysis includes leisure-time activities of moderate intensity, defined as an intensity of three or more metabolic equivalents (MET), or vigorous intensity, defined as six or more METs; these are the intensity levels recommended by physical activity guidelines.

The indispensable significance of regular exercise in cancer prevention cannot be emphasized enough. It intricately modulates many biological pathways and mitigates myriad risk factors associated with the onset of various cancers.

Focusing on holistic health principles by adding regular physical activity into our daily routines, cultivating a healthy lifestyle with stress management, and abstaining from detrimental habits like smoking, drug use, excessive alcohol, overeating, and chronic stress, we can significantly reduce the risk of cancer and boost our overall health and well-being.

Thank you for reading my perspectives. I wish you a healthy and happy life.

If you found this story helpful, you may also check out my other articles on NewsBreak. As a postdoctoral researcher and executive consultant, I write about important life lessons based on my decades of research and experience in cognitive, metabolic, and mental health.