Bowel cancer is a life-threatening illness that results from an abnormal growth of cells in the large intestine or rectum. Drinking alcohol, even in moderation, can increase the risk of several cancers, including bowel cancer. Alcohol can cause cells to accumulate carcinogenic compounds and can have disruptive effects on the intestinal lining. As such, healthcare professionals recommend limiting alcohol consumption as an important aspect of bowel cancer prevention, among other lifestyle modifications.

Introduction

Bowel cancer, also known as colorectal cancer, is a disease characterised by an abnormal mass of cells in the large intestine or rectum.¹ Since the colon is involved in food absorption and excretion of faecal waste, bowel cancer can result in various symptoms such as weight loss, fatigue, bloody stool, and constipation or diarrhoea.²

In cancer, these cell masses – known as tumours – have mutated and strongly differ from the surrounding tissue.¹ Cancerous or malignant tumours can spread to other parts of the body, such as the stomach, lungs and brain. Therefore, early diagnosis while the cancer is still in its initial stages, along with prompt treatment through surgery and anticancer medications, is fundamental.²

In the United Kingdom, bowel cancer is the 4^th most common type of cancer with over 40,000 cases and over 16,000 deaths every year. Bowel cancer can occur in every age but it is more common in the elderly with 4 out of 10 diagnoses in the UK occurring in those aged 75 or over.³

Importantly, as much as 54% of all bowel cancer cases are potentially preventable through lifestyle modifications and early identification of risk factors.³ People who have a family history of bowel cancer or certain intestinal conditions, such as Crohn’s Disease and Ulcerative Colitis, have an increased lifetime risk of bowel cancer. Lifestyle-related risk factors for bowel cancer include obesity, high-fat diet, excessive consumption of red and processed meat, and lack of physical activity.⁴

In addition, excessive alcohol consumption is another significant cause of bowel cancer, being associated with 1 in 17 cases of bowel cancer in the UK.⁵ In fact, studies show that heavy drinking – equivalent to 50g/day or 3 drinks per day – can increase one´s risk of bowel cancer by 1.5 times.⁶ Understanding the effects of alcohol on the intestines and how to reduce your risk can help prevent cancer and maintain bowel health.

Pathophysiology of bowel cancer

Typically, bowel cancer starts as a non-invasive cell growth called an adenomatous polyp. These cells can undergo genetic mutations to become more undifferentiated – meaning they differ increasingly from normal gut tissue – and eventually develop into cancerous tumours known as carcinomas. Carcinomas are made up of rapidly dividing cells that infiltrate nearby lymph nodes and travel to distant organs through the lymphatic system and bloodstream to form a secondary tumour, known as metastasis, at a different site.

Although some patients do not experience any symptoms, bowel cancer usually disrupts the normal functioning of the bowels primarily due to the physical presence of a tumour within the colon or rectum. The cell mass can obstruct the passage of stool and result in constipation, or they can also irritate the intestinal lining causing inflammation and pain.

Depending on the tumour location and the stage of the disease, other symptoms such as diarrhoea, bloody stool and bowel wall perforation can also occur. As cancer cells alter metabolic demands and intestinal tumours interfere with nutrient absorption, patients often also present with systemic symptoms such as weight loss, fatigue and anaemia.⁷

Diagnosis and bowel cancer management

Bowel cancer diagnosis is often difficult and requires multiple steps. Usually, doctors will start by taking a detailed medical and family history and will prescribe appropriate investigations if they suspect the patient may be at risk of having bowel cancer. Stool samples are often collected to check for the presence of macroscopic or microscopic blood, which can help determine whether the patient requires a colonoscopy.

This is a procedure in which a long, flexible tube with a camera is used to visually inspect the entire colon and rectum, and possibly remove a biopsy of tissue for inspection. Advanced imaging techniques, such as CT and MRI scans, can help determine the extent of cancer spread within the abdomen and to distant organs (staging).

Bowel cancer management involves a combination of treatments tailored to the cancer's stage and location. Surgery is often the primary treatment, aiming to remove the tumour and surrounding tissues. Adjuvant therapies, such as chemotherapy and radiotherapy, may follow surgery to eliminate any remaining cancer cells and reduce the risk of recurrence.

Targeted therapies and immunotherapy are new treatments that can be used to specifically attack cancer cells or boost the immune system to fight cancer.⁸ In the UK, bowel cancer has a 10-year survival rate of 53%, however; prognosis varies significantly based on age.³ For advanced stages, palliative care focuses on relieving symptoms and improving quality of life.⁸

The link between alcohol and bowel cancer

Alcohol consumption is associated with an increased risk of developing various cancers including of the liver, stomach, mouth, oesophagus, breast, colon and pancreas. In 2020, just over 4% of all new cancers worldwide were potentially attributed to alcohol.⁹ Different mechanisms have been proposed to explain this link. Notably, alcohol metabolism is known to cause a buildup of acetaldehyde and reactive oxygen species (ROS) in cells, which can damage cell DNA and induce cancer.¹⁰

DNA molecules frequently undergo modifications that alter the activity of certain genes. One way this occurs is through the addition of a methyl group, a process that is usually tightly regulated. Alcohol can increase or decrease DNA methylation which may contribute to the generation of cancerous cells. Alcohol may also affect the availability of important nutrients, such as folic acid, which are essential for DNA repair.¹¹

In some cases, alcohol has specific effects that influence the development of certain types of cancer. For example, heavy alcohol consumption can raise oestrogen levels, increasing the risk of breast cancer. Alternatively, exposure of the mouth, throat and oesophagus to alcoholic beverages may have local carcinogenic effects.¹²

Regarding colorectal cancer, research shows that both heavy and moderate drinking are significant risk factors. Exposure to acetaldehyde and other metabolites of alcohol can affect cell DNA and activate carcinogenic signalling cascades.¹³ Alcohol can also affect the gut microbiome and irritate the epithelial lining, leading to increased inflammation and promoting chronic cell damage and replacement, which can raise the risk of cancer-causing mutations.⁶

How to reduce your risk of bowel cancer

Many of the risk factors for bowel cancer are easily modifiable through lifestyle changes. Some important measures that can be taken include:

• Limit the consumption of red and processed meat
• Maintain a healthy weight
• Be physically active
• Avoid drinking more than the recommended of up to 8 drinks per week for women and 14 for men
• Increase dietary intake of fibre
• Quit smoking¹⁴

Another important part of prevention is regular screening. In the UK, the National Health Service (NHS) recommends that people aged 60-74 take a faecal immunochemical test every two years to screen for blood in stools.¹⁵

Importantly, even moderate drinking can increase the risk of colorectal cancer and negatively impact intestinal health. Below are some tips to help lower your alcohol intake:

• Set clear limits on alcohol intake
• Choose to have some alcohol-free days each week
• Find alternative activities to unwind, like exercise or hobbies
• Keep track of your drinking habits to identify patterns and triggers
• Find low-alcohol drinks to replace your usual beverages
• Ask for help from family, friends and/or healthcare providers if you feel like your drinking is getting out of control¹⁶

Summary

Bowel cancer is a life-threatening health condition, in which a mass of invasive undifferentiated cells develops in the colon or rectum. The cancerous cells can then spread through the blood and lymph to distant organs forming metastases. Bowel cancer diagnosis typically involves a combination of medical history, stool analysis and colonoscopy. The majority of patients survive for over 10 years with treatment through surgery and anticancer therapies.

Different genetic and environmental factors have been associated with an increased risk of bowel cancer. Some of these include family history, old age, fibre-deficient diet, obesity, and excessive consumption of red meat. Importantly, 1 in 17 cases of bowel cancer in the UK can be attributed to alcohol consumption. Studies show that heavy, and to a lesser extent, moderate, alcohol intake can produce harmful amounts of toxic metabolites that damage our cells and promote carcinogenesis. In the intestines, alcohol can also disrupt the normal microbiota and promote inflammation.

As such, since over half of all bowel cancer cases in the UK are preventable, it is fundamental to spread awareness about possible prevention and early detection measures. An important health recommendation is to limit alcohol consumption to avoid alcohol´s toxic effects on the gut and reduce long-term cancer risk.