Bowel cancer, also known as colorectal cancer, is one of the most common cancers worldwide. Although it has traditionally been associated with people over 50, an important and concerning change has emerged: bowel cancer is increasingly being diagnosed in younger adults.
According to the World Health Organization (WHO), colorectal cancer accounts for approximately 10% of cancer cases worldwide and is the second leading cause of cancer-related death. Most cases still occur in older adults, but rates among people under 50 have risen substantially in many countries.
Researchers are actively investigating why this is happening. There is unlikely to be one single explanation. Instead, the increase may involve a combination of diet, lifestyle, metabolic health, environmental exposures, genetics and potentially changes within the gut microbiome.
Bowel cancer in younger adults
Early-onset colorectal cancer generally refers to bowel cancer diagnosed before the age of 50. Over the past three decades, incidence rates in younger adults have approximately doubled worldwide, and around 10% of new colorectal cancer cases are now diagnosed in this age group, according to the International Agency for Research on Cancer (IARC).
This matters because younger people may not consider themselves at risk. Symptoms can sometimes be attributed to more common digestive conditions, potentially delaying medical assessment and investigation.
The key message: bowel cancer remains much more common in older adults, but persistent or unexplained bowel symptoms should not be dismissed because of a person’s age.
Why might bowel cancer be becoming more common?
Changes in our diet
Diets high in red and processed meat and low in fruit, vegetables and fibre are associated with increased colorectal cancer risk. Modern eating patterns may also contain more highly processed foods, refined carbohydrates and saturated fat.
Fibre supports normal bowel function and is fermented by bacteria in the colon to produce short-chain fatty acids, including butyrate, which helps maintain the cells lining the colon.
Obesity and metabolic health
Obesity and type 2 diabetes have been associated with colorectal cancer risk. Possible mechanisms include insulin resistance, higher circulating insulin, chronic low-grade inflammation and other metabolic changes.
However, obesity does not explain every case. Young people who are physically active and of normal weight can still develop bowel cancer.
Increasingly sedentary lifestyles
Many people now spend long periods sitting at desks, driving or using screens. Physical inactivity is an established risk factor, while regular physical activity is associated with reduced colorectal cancer risk.
Movement can influence body weight, insulin sensitivity, inflammation and bowel function.
Alcohol and smoking
Alcohol consumption and tobacco use are recognised risk factors for colorectal cancer. With alcohol, risk rises with consumption, while tobacco exposes the body to carcinogenic substances that can contribute to genetic damage over time.
These exposures may begin many years before cancer develops, which is why researchers are interested in adolescence and early adulthood.
Could the gut microbiome be involved?
The gut microbiome is the enormous community of microorganisms living within our gastrointestinal tract. It is shaped by diet, antibiotics, lifestyle, environment and exposures beginning early in life.
Researchers are investigating whether particular microbiome changes could contribute to colorectal cancer by promoting inflammation or producing substances capable of damaging DNA. This is an important emerging field, not yet a complete explanation.
Antibiotics and early-life exposures
The intestinal microbiome begins developing in infancy and can be influenced by diet, breastfeeding, mode of birth, antibiotics and environmental factors.
Researchers are examining whether childhood or early-adult exposures may influence risk decades later. Antibiotics can alter the microbiome, but they should not currently be considered an established cause of the rise in early-onset bowel cancer.
Genetics still matter
Inherited conditions such as Lynch syndrome and familial adenomatous polyposis can substantially increase risk, and a strong family history is also important.
However, hereditary syndromes account for only a proportion of cases in younger people and cannot explain the rapid population-level increase by themselves.
Recognising the symptoms of bowel cancer
Persistent bowel symptoms should not be ignored simply because someone is young. Symptoms that warrant medical assessment can include:
- Blood in the stool or rectal bleeding
- A persistent change in bowel habit
- Unexplained diarrhoea or constipation
- Persistent or unexplained abdominal pain
- Unexplained weight loss
- Persistent fatigue
- Iron-deficiency anaemia or low iron
- A feeling that the bowel is not emptying fully
These symptoms do not necessarily mean that someone has bowel cancer. Many common and non-cancerous gastrointestinal conditions can cause similar symptoms. However, persistent or unexplained symptoms should be discussed with a GP rather than self-diagnosed.
The importance of earlier investigation
There is no single home test that can diagnose or completely exclude bowel cancer. Depending on a person’s symptoms, age, family history and other risk factors, a doctor may recommend blood tests, a Faecal Immunochemical Test (FIT) to detect small amounts of blood in the stool, other stool investigations, imaging or colonoscopy.
A negative FIT is not a complete “all clear”
A negative FIT result does not completely exclude colorectal cancer. If symptoms are persistent, worsening or concerning, medical assessment remains important and should be based on the overall clinical picture.
Can we reduce our risk?
Not every case of bowel cancer can be prevented, and people who lead healthy lifestyles can still develop the disease. However, several established risk factors are modifiable.
Perhaps equally importantly, become familiar with what is normal for your own bowel habits and seek medical advice when persistent changes occur.
Awareness without unnecessary alarm
At GastroLife, we believe that increased awareness of digestive health and appropriate investigation of persistent gastrointestinal symptoms are extremely important.
The increase in bowel cancer among younger adults does not mean that common symptoms such as bloating, diarrhoea, constipation or abdominal discomfort are usually caused by cancer—they are not. It does reinforce why persistent or unexplained symptoms should not automatically be assumed to be IBS, food intolerance or another benign digestive condition without appropriate medical assessment.
Research into early-onset bowel cancer is continuing rapidly. Diet, obesity, metabolic health, physical inactivity, alcohol and smoking are established or recognised risk factors, while the gut microbiome and earlier-life exposures are important emerging areas of research.
There may ultimately be no single explanation. The increase is likely to reflect a complex interaction between genetics, environment, lifestyle, metabolism and potentially the microorganisms living within the gut.
Persistent symptoms? Speak with your GP.
Rectal bleeding, unexplained weight loss, a persistent change in bowel habit or unexplained iron-deficiency anaemia should be medically assessed. FIT may form part of an investigation, but it does not replace clinical advice.
Learn about the FIT test
