Introduction

Bowel cancer refers to cancer, uncontrollably dividing cells, residing in the colon and/or rectum. It is estimated to account for approximately 10% of global cancer cases globally by the World Health Organisation (WHO).^1,2 The development of bowel cancer usually manifests from non-cancerous growths (termed ‘polyps’), which have been linked to lifestyle factors including a poor diet, regular long periods of sitting, obesity, smoking, and excessive alcohol consumption. It has been shown that both the incidence and impact of bowel cancer can be significantly reduced by adopting a healthy lifestyle and avoiding these risk factors.¹

Physical activity has proven to be significantly beneficial to health by scientists countless times over the decades. This article addresses the epidemiology, or associated risk, of bowel cancer, its associations with physical activity, and the potential benefits of physical activity in preventing the development of cancer in the bowel.

Epidemiology of bowel cancer

Incidence and prevalence

• In 2020, there were 1.9 million new diagnoses of bowel cancer worldwide, coinciding with over 930,000 associated deaths
• Europe and Australasia have the highest incidence of bowel cancer, whilst eastern regions of Europe had the highest mortality associated with bowel cancer in 2020¹ 
• It is estimated that 1 in 15 to 18 individuals will face a bowel cancer diagnosis in their lifetime, according to Bowel Cancer UK² 
• The WHO predicts a 63% increase in occurrence and a 73% increase in mortality by 2040 based on current figures, raising significant concern and highlighting a need for intervention.¹ 

Risk factors

The following factors have been shown to have an association with an increased risk of bowel cancer:¹

Age 

Individuals aged 50 and over are at a greater risk of developing bowel cancer and the risk continues to increase with age.

Family history 

Individuals with close relatives who have a history of bowel cancer or genetic conditions have an increased risk of developing polyps that will likely develop into bowel cancer (such as Lynch syndrome and familial adenomatous polyposis).

Personal history 

Individuals who have previously had bowel cancer or specific types of polyps are at a higher risk.

Lifestyle

Unhealthy lifestyle habits are associated with bowel cancer development. These include: 

• A poor diet with high amounts of processed meat and low quantities of fruit and vegetables
• Frequently sitting for long periods
• Obesity 
• Smoking
• Alcoholism

Physical activity and bowel cancer

Biological mechanisms 

Inflammation

In response to physical activity, the body releases myokines, hormones released when skeletal muscles connecting muscle to bone contract to allow movement. These myokines have an anti-inflammatory effect, reducing redness, swelling, and pain.³ When physical activity does not occur and these myokines aren’t released, any inflammation in the body is less combated. Inflammation that manifests for 3 months and beyond is considered chronic, which causes damage to DNA replication, contributing to uncontrolled cell division and prerequisite cancer.⁴ 

This biological mechanism is often associated with bowel cancer in patients who are obese, lead lifestyles that are sitting-intensive, and ultimately less physically active. Therefore when physical activity is increased, there is less associated inflammation and reduced risk of bowel cancer development.

Insulin resistance 

Insulin resistance, a reduced or complete lack of insulin response, is commonly associated with obesity and type II diabetes, and subsequently the progression of these conditions to bowel cancers. 

Scientists have proposed the resistance to the blood sugar-regulating hormone is attributed to defects in either:⁵

• Regulating insulin levels, resulting in higher levels of insulin in the blood than the recommended levels (hyperinsulinemia)
• Desensitised insulin receptors, insulin-like and/or hybrid insulin growth factor 1 receptors, interact with insulin in the blood to regulate blood sugar levels

Although the exact mechanism is unknown, it is theorised by scientists that since cancer cells have a high energy expenditure, requiring around 200 times the amount of sugar to function than normal cells, cancer is more likely to develop when insulin regulation and detection are poor, and therefore blood sugar levels are higher.⁶ There is a wealth of evidence to show that physical activity improves insulin sensitivity, preventing a build-up of sugar in the blood and therefore reducing the risk of cancer.⁷

Gut microbiota 

The bacterial composition in the gut, otherwise known as the gut microbiota or microbiome, is an essential part of human health. 

Current research points to a dysbiosis, or imbalance in the specific bacteria lining the gut, leading to the manifestation of many diseases including bowel cancer. Scientists have theorised that altered gut microbiota, often caused by other illnesses or lifestyle factors, interact with the colonic epithelium lining the walls of the bowel and the immune system. This will then cause the release of metabolites, proteins and macromolecules, ultimately leading to cancer development.⁸ Physical activity has been shown to contribute to a diverse and healthy gut microbiota, preventing the development of dysbiosis and therefore the development of diseases including bowel cancer.⁹

Behavioural mechanisms

Body weight

Obesity and excessive body fat, particularly when carried around the waist, predispose a person to the development of bowel cancer. 

Approximately 11% of bowel cancer diagnoses made in the UK are attributed to being overweight or obese.¹⁰ This is due to fat cells releasing molecular signals, such as:¹¹

• Growth hormones, which encourage the division and growth of cells aid cancer development
• Immune cells, which traffic to fat cells and cause inflammation
• Sex hormones, especially in post-menopausal women when fat cells produce the female sex hormone oestrogen, causing cell division

A higher body weight is often associated with a reduction in physical activity, demonstrating the need for physical activity to prevent the accumulation of fat cells.¹¹

Dietary habits and bowel regularity 

The diet is heavily associated with the motility of the gut. A diet rich in fibre, obtained from whole grains, pulses, fruit and vegetables, and low in processed and red meats promotes more regular bowel movements.¹² 

The muscles in the bowel respond to activity, meaning the more physically active a person is, the more likely they are to have toned bowel muscles. Bowel muscle with good tone contributes to greater bowel regularity.¹³ When bowel muscles are not toned, individuals can suffer from constipation. The American College of Gastroenterology’s 2012 study showed chronic constipation was associated with an increased risk of bowel cancer, solidifying the importance of physical activity in prevention.

Types of physical activity beneficial for bowel cancer prevention

There are 3 main subtypes of physical activity beneficial for preventing bowel cancer:¹⁴

• Aerobic exercise, consisting of rhythmic movements that elevate the heart rate and breathing for an extended period of time such as:
  • Walking 
  • Running 
  • Swimming 
  • Cycling
  • Dancing

• Resistance training, also known as weight/strength training, increases muscle tone by using:
  • Weights 
  • Resistance bands
  • Body weight (calisthenics)

• Combination approaches, integrating aerobic and resistance training. Examples include:
  • Circuit training 
  • Cross-training
  • High-intensity interval training (HIIT)

All subtypes of physical activity improve: 

• General health and well-being 
• Reduce inflammation 
• Contribute to a diverse gut microbiota 
• Lower insulin resistance 
• Control body weight 
• Sustain good muscle tone in the gut 

All of these factors lower the risk of bowel cancer.

Recommendations for physical activity

The WHO recommend the following physical activity guidelines for individuals between the ages of 18 and 64:¹⁵

• A minimum of 150-300 minutes of moderate-intense aerobic exercise
• Or 75-100 minutes of either moderate and vigorous, or vigorous aerobic exercise in a week.
• 2 or more days of moderate to intense muscle strengthening exercises, which involve all major muscle groups.
• Limiting time spent sitting and replacing it with light exercise.

Case studies and real-world examples

A meta-analysis study concluded a 24% reduction in the relative risk of bowel cancer for individuals assigned male at birth and a 21% reduction in those assigned female at birth when physical activity is implemented. This greatly emphasises the importance of physical exercise in preventing bowel cancer development.¹⁶ 

FAQs

What are the symptoms of bowel cancer?

The symptoms of bowel cancer include:¹

• Changes in bowel regularity, such as diarrhoea, constipation, or stool narrowing
• Blood in the stool, or rectal bleeding
• Cramping, pain or bloating in the abdomen that does not go away
• Sudden and unexplained weight loss 
• A lack of energy and extreme tiredness where rest is unchanged
• Iron deficiency anaemia caused by blood loss

What are the survival rates of bowel cancer?

When detected and diagnosed early, bowel cancer is easily treatable. The number of deaths caused by bowel cancer has been dropping in the UK since 1970, and it is estimated that 16,800 die from bowel cancer per year in the UK.²

Summary

• Although bowel cancer is one of the most common types of cancer, its associations with lifestyle factors mean many cases can be easily prevented
• Making small behavioural changes, by increasing physical activity and decreasing the amount of time spent sitting, influences biological mechanisms and reduces the predisposition to developing bowel cancer
• A multitude of data supports the link between physical activity and its impact on bowel cancer patients and emphasises the importance of being active with or without an impending cancer diagnosis