Walk to stave off bowel cancer: Experts pinpoint how many hours a week

Walking for just five hours a week could dramatically reduce your risk of developing or dying from deadly digestive system cancers, including bowel, liver and pancreatic.

Regular exercise has long been lauded as a crucial way to not only help stave off cancer, but also lower the chances of it spreading.

Now, groundbreaking research published in medical journal JAMA Oncology, has shown those who maintain a moderate level of physical activity, by getting their heart rate up for around 17 hours a week, see a significant decrease in cancer risk.

But, the researchers noted, consistency is key—you need to stick to it for three decades.

In 2024 alone, digestive system cancers, including cancers of the mouth, throat, esophagus, stomach, bowel, pancreas gallbladder and liver, accounted for 40 per cent of all cancer-related deaths. 

And whilst it’s well-known that sedentary lifestyles, being overweight, smoking and excessive alcohol consumption can increase the risk of the disease, until now relatively little was known about how much exercise, and over how many years, is needed to lower the risk. 

In the new study, researchers led by Dr Yiwen Zhang, at Harvard T.H Chan School of Public Health, combined data from three large US cohorts, following 231,067 participants for around 32 years. 

At the beginning of the study, all participants were cancer free and had no history of heart disease.

Participants completed surveys every two to four years assessing medical history, how active they were during leisure time, and diet, with more than 90 per cent of participants submitting data within each cycle. 

With regards to physical activity, participants were asked, on average, how long they had spent doing various activities per week, over the past year.

These activities included walking, jogging, running, cycling, swimming, tennis or squash, other aerobic activities, low intensity exercise and working outdoors. Information on weight lifting was later added to the questionnaire. 

They also recorded how many flights of stairs they climbed a day. 

Over the course of the study, self reported cancer diagnoses were verified through medical records, and any deaths—which totalled 3,791 by the end of the study—were confirmed by autopsy reports. 

A total of 6,358 digestive system cancer cases were diagnosed.  

The researchers found that in this cohort, made up of healthy 40-75-year-olds, higher levels of leisure time physical activity was associated with lower digestive cancer risk and death. 

They added that whilst the optimum duration of physical activity was around 50 hours of exercise, consistency was crucial. 

Sustaining around 17 MET hours a week—which is around five hours of brisk walking or two hours of running—over 30 years was found to offer the greatest benefits, lowering the risk of digestive system cancer by 17 per cent. 

MET refers to ‘metabolic equivalent of task’ – a scientific unit that measures energy burned. 

This suggests that much higher levels of physical activity than currently recommended are needed to achieve the greatest benefits, with the NHS recommending adults aged 19-64 to aim for at least 2.5 hours of moderate intensity activity a week. 

In the US, this more than doubles the recommended guidelines. 

Interestingly, however, more than 17 hours of consistent physical activity were not associated with extra benefit. 

The researchers theorised that the protective benefits do not come from weight loss alone. 

‘Physical activity may have systematic anticancer effects, such as improving insulin sensitivity, lowering inflammation and enhancing immune function,’ Dr Zhang  explained. 

He added that exercise may also aid digestion, reducing the amount of time potential toxins spend in contact with the bowel wall, minimising the risk of contamination. 

‘Furthermore, maintaining consistent adequate physical activity may be particularly beneficial for preventing cancer, which usually takes a long time to develop.’ 

Previous research has suggested that exercise can trigger the release of chemicals in the blood that help the immune system hunt and destroy cancer cells.

Studies have also found that regular exercise reduces levels of inflammatory proteins in the body that are known to fuel the development of tumours

Commenting on the landmark study, cancer experts from the University of Sydney said the results may help doctors to offer reassurance to patients who cannot achieve 17 hours of exercise a week. 

Writing in the journal JAMA oncology, they said: ‘Even smaller amounts of exercise performed consistently for those unable to reach the goal of 17 hours a week will be beneficial. 

‘Government, social and health systems must adopt a holistic approach to human health to embed opportunities for physical activity, while providing structured exercise programs to support individuals to increase their physical activity and experience its benefits to their overall health.’ 

The need for such solutions is clear. A recent analysis by One Cancer Voice predicted that by 2040, the most common cancers – breast, prostate and lung – will hit unprecedented levels, while more than 63,000 cases are predicted in children and young people.

England has experienced one of the fastest rises in early-onset bowel cancer worldwide, with an average annual increase of 3.6 per cent between 2007 and 2017 among under-50s. 

Although the disease remains relatively rare in younger adults – accounting for about five per cent of cases – this upward trend has baffled experts.

Moreover, bowel cancer death rates among under-50s were projected to rise by 39 per cent for women and 26 per cent for men in 2024 compared with the average for the period from 2015 to 2019.

Regardless of survival, it is a life-changing diagnosis, not least because it often involves surgery, months of chemotherapy, radiotherapy and hormone treatments that can leave some suffering debilitating side-effects.

Generally speaking, symptoms of gastrointestinal cancers—including oesophageal, stomach, bowel, pancreatic and liver cancer—don’t occur until the disease has become more advanced. 

Patients with esophageal cancer may experience difficulty swallowing whilst those with stomach or bowel cancer may experience abdominal pain, and a change in bowel movements. Liver and pancreatic cancer can also present with similar symptoms. 

A lump in the stomach, bloating, unexpected weight-loss and fatigue are among other common signs.