New research has unveiled a concerning link between alcohol consumption and an increased risk of certain bowel cancers, particularly rectal cancer. A comprehensive twenty-year study conducted by the National Cancer Institute (NCI) in the US, involving over 8,000 participants, indicates that consuming 14 or more alcoholic drinks per week – equivalent to two drinks nightly – significantly elevates the risk of colorectal cancer and nearly doubles the risk of rectal cancer compared to light drinkers.

The study found that individuals who consumed between seven and 13 drinks weekly actually had a lower risk of colorectal cancers. However, those drinking 14 or more alcoholic drinks per week faced a 25 percent higher risk of developing colorectal cancer and a striking 95 percent increased risk specifically for rectal cancer, when compared to light drinkers (defined as having less than one drink per week). This elevated risk was attributed to heavy drinking throughout adulthood, though encouragingly, researchers observed no increased risk among former drinkers, suggesting that reducing or ceasing alcohol intake can help safeguard against bowel cancer.

Dr. Erikka Loftfield, an epidemiologist at the National Cancer Institute and co-author of the study, highlighted the significance of their findings: "Our study is one of the first to explore how drinking alcohol over the life course relates to both colorectal adenoma [non-cancerous tumours] and colorectal cancer risk." She added that while data on former drinkers was sparse, the indication that their risk might return to that of light drinkers was encouraging. Dr. Loftfield emphasized that cumulative exposure over a person's lifetime, not just drinking habits in older age, might be a crucial factor for cancer risk.

The research, published in the journal Cancer, analyzed health records of 88,092 US adults enrolled in the Prostate, Lung, Colorectal, and Ovarian (PLCO) cancer screening trial who were initially cancer-free. Over approximately 20 years of follow-up, 1,679 cases of colorectal cancer were identified. The study also noted that occasional moderate or heavy drinking did not carry the same risk as consistent heavy drinking. Interestingly, current drinkers with a moderate average lifetime intake (less than 14 drinks per week) exhibited a lower cancer risk, particularly for distal colon cancer, compared to those with the lowest alcohol intake. Dr. Loftfield explained that the inverse association with colorectal cancer was strongest in the screening arm of the trial, suggesting that screening might modify the link between alcohol consumption and CRC risk.

Colorectal cancer, also known as bowel cancer, refers to cancer found anywhere in the large bowel, encompassing the colon and rectum. It is one of the most common cancers in the UK and was recently identified as the leading type of cancer diagnosed in Americans aged 50 and under. Rectal cancer, specifically, forms in the tissues of the rectum, with symptoms including blood in the stool or changes in bowel habits. While numerous risk factors exist for bowel cancer—such as heavy drinking, smoking, and poor diet—they typically increase the likelihood of DNA damage in cells that can lead to cancer, rather than directly causing it.

Researchers propose several mechanisms for the link between alcohol and abnormal cell growth. Firstly, alcohol produces acetaldehyde, a known carcinogen that causes DNA mutation and oxidative stress in the colon and rectum. This toxin also hinders the absorption of folate, which is associated with an increased risk of certain cancers, like colon cancer. Additionally, alcohol consumption is known to damage the gut microbiome, leading to cell death. Conversely, the authors acknowledged that moderate alcohol intake might reduce inflammation and lower DNA damage, potentially explaining the lower risk observed in those adhering to drinking guidelines.

The NHS recommends that individuals consume no more than 14 units of alcohol per week, which equates to approximately six glasses of wine, stating there is no completely safe level of drinking. More than half of bowel cancer cases—54%—are considered preventable, with risk factors including eating processed meat, being overweight, and drinking alcohol, according to Cancer Research UK. To combat this, the NHS in England is enhancing the accuracy of bowel cancer tests by lowering the blood detection threshold in stool tests, enabling earlier detection and treatment, often before symptoms emerge. This move is expected to save hundreds of lives. The late Dame Deborah James, known as the 'bowel babe,' significantly raised public awareness of the disease, which tragically claimed her life in 2022 at the age of 40, raising over £11.3 million for Cancer Research.