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The Powerful Link Between Exercise and Decreased Cancer Risk

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Among the numerous benefits associated with regular physical activity, a particularly noteworthy connection has emerged: the role exercise plays in decreasing risk of cancer recurrence. This article aims to shed light on the risk reduction statistics of exercise following a cancer diagnosis and the mechanisms by which this may occur.


The Effects of Exercise vs. Inactivity on Cancer Risk

Per current guidelines, the American Cancer Society recommends 150-300 minutes of moderate activity each week in those diagnosed with or with a history of cancer. This includes at least two days of resistance or strength training exercises. It has been well-demonstrated that intentional movement mitigates the risk of cancer development. Most notably, the International Agency for Research on Cancer of the World Health Organization estimates a 20-40% decrease in the risk of developing breast cancer among the most physically active women, regardless of menopausal status, type, or intensity of activity. [[i]] A systemic review examining the 2018 Physical Guidelines Advisory Committee Scientific Report concluded when comparing individuals in the highest category of physical activity versus the lowest, there was 10-20% relative risk reduction in breast, colon, bladder, endometrial, esophageal, renal, and gastric cancers. [[ii]]

The effects of prolonged sitting or inactivity has also been well-studied in the cancer context. 1,535 cancer survivors self-reporting activity levels were followed for a median of 4.5 years. A staggering five-fold (400%) increase in all-cause mortality, cancer-specific mortality, and noncancer mortality was observed in those collectively sitting more than eight hours per day. Conversely, in those survivors who were more physically active, there was a 66% lower risk of all-cause mortality, 68% lower risk of cancer-specific mortality, and 64% decreased risk of noncancer mortality. [[iii]]


Decreasing Cancer Recurrence with Exercise

While regular physical activity may play a substantial role in decreasing risk of cancer development, emerging research demonstrates a powerful link between exercise and decreased risk of cancer recurrence in those already diagnosed. In an analysis of eight studies involving 15,298 patients diagnosed with breast, colorectal, and prostate cancer, researchers concluded higher volumes of post-diagnosis activity was associated with a 45% reduction in risk of cancer recurrence. [[iv]] Another study, involving 1,696 patients with surgically resected stage III colon cancer enrolled 21-56 days following the operation, revealed the positive impact of physical activity throughout adjuvant chemotherapy. Followed closely for six years, these patients self-reported levels of exercise with the definition of “physically active” being equivalent to 150 min of brisk walking per week. Amongst several parameters, risk of disease recurrence was always lower in the physically active group. Most notably, postoperative physical activity within the first year of treatment was the most statistically significant in preventing cancer recurrence and improving overall survival. [[v]]

In addition, a similar study with 832 participants with stage III colorectal cancer reporting on activity level six months following surgical resection of the tumor and adjuvant chemotherapy showed improved disease free and overall survival that was NOT influenced by sex, body mass index, number of involved lymph nodes, age, baseline performance status, or chemotherapy received. [[vi]] Following a stage I, II, or III breast cancer diagnosis, 2,987 female patients were assessed based on physical activity level. The greatest benefit occurred in women who performed three to five hours of brisk to average-paced walking per week. Most importantly, participation in physical activity after diagnosis was associated with a 24% reduction in disease recurrence and 45% reduction in mortality. [[vii]]


How Exercise Impacts the Body and Reduces Cancer Risk

Brown et. al. hypothesizes physical activity is involved in several mechanisms throughout the human body that reduce risk of cancer recurrence. These mechanisms involve favorable changes in metabolic growth factors, inflammation, and immune function. [[viii]] Overall, this creates an environment that is inhospitable to metastatic initiation and progression. It is a well-established phenomenon that cancer cells often overexpress insulin receptors, which in turn may activate several pathways that allow for malignant cell growth. A study evaluating fasting insulin and outcome in early-stage breast cancer patients showed higher fasting plasma insulin was associated with a two-fold higher risk of distant recurrence and three-fold higher risk of mortality.

[[ix]] A meta-analysis performed following publication of this study confirmed fasting plasma insulin was decreased in women with stage I-III breast cancer with an established physical activity routine. [[x]] Another proposed mechanism for how exercise decreases risk of recurrence is via regulation of immune function. Circulating tumor cell DNA testing allows for the ability to detect microscopic residual disease following curative-intent therapy or to detect disease recurrence. Consistent exercise directly affects cell viability, inhibits growth, and decreases metabolic potential of circulating tumor cells. [[xi]] A study published in 2018 showed lower occurrence of circulating tumor cell DNA in patients with stage I-III colorectal cancer with a physical activity routine averaging 150-300 minutes per week. [[xii]]


Exercise and Cancer Care

In summary, the amalgamation of evidence underscores the pivotal role of physical activity in the continuum of cancer care. As the scientific community delves deeper into understanding these mechanisms, the call for integrating structured physical activity into cancer care regimens becomes increasingly compelling, offering hope for improved outcomes and enhanced quality of life for cancer survivors.

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