Finding time for exercise can feel difficult, but new research suggests that cancer prevention may not depend only on long workouts.
Simply shifting a small part of the day from inactivity to movement was linked to a lower risk of cancer in a large UK study.
Researchers from University College London found that replacing 15 minutes of sedentary time with 15 minutes of movement was associated with about a 2% reduction in cancer risk. A similar association appeared when 15 minutes of sleep was statistically replaced with movement.
The research was published in BMC Medicine and was led by Dr. John Mitchell from UCL’s Division of Surgery and Interventional Science. It used data from the UK Biobank.
The study included 59,218 people, with an average age of 61.7 years. Slightly more than half of the participants were women.
Instead of asking participants how much they thought they moved, researchers used wearable activity monitors. These devices recorded movement patterns and helped the team estimate how much time people spent sleeping, sitting, standing or being physically active.
The participants were followed for about eight years. During that time, 2,385 cases of cancer included in the analysis were recorded.
Researchers then used mathematical models to examine how changing the balance of daily activities might relate to cancer risk. Because a day always has 24 hours, adding time to one activity necessarily takes time away from another.
This approach allowed the team to ask questions that are closer to real-life choices. For example, what is the difference between spending 15 minutes sitting on the sofa and using those 15 minutes to walk or do another physical activity?
The analysis found that greater movement was generally associated with lower cancer risk. Replacing either sedentary time or sleep with movement for 15 minutes was linked to roughly a 2% lower risk.
Researchers also looked at what happened when movement was replaced by less active behavior. Swapping 30 minutes of movement for sitting was associated with an 8% higher cancer risk.
When 30 minutes of movement was replaced with sleep, the modeled increase in risk was about 7%. This result should not be taken to mean that sleep causes cancer or that people should reduce the sleep their bodies need.
Instead, the study is about the balance of behaviors across the day. Someone who sleeps enough but spends many waking hours sitting may have opportunities to replace some of that sitting with movement without cutting healthy sleep.
The study also examined vigorous physical activity. This is activity that noticeably raises the heart rate and breathing and may make a person sweat.
Examples do not have to involve a gym. Running to catch public transport, rushing up a flight of stairs or carrying heavy shopping can create short bursts of vigorous movement.
The researchers’ modeling suggested that among people who were already active, replacing only two or three minutes a day of vigorous activity with sitting, sleep or light activity was associated with an increase in cancer risk. This finding emphasizes the possible value of maintaining higher-intensity movement over time.
Mitchell said this is particularly important as active people grow older. People often become less active with age, so preserving existing activity may be just as important as encouraging inactive people to start moving.
Scientists have several ideas about why movement may protect against some cancers. Physical activity helps regulate body fat, blood sugar and insulin and can influence inflammation and hormone levels.
These processes matter because obesity, long-term inflammation and abnormal hormone or insulin signals can contribute to the development of certain cancers. Physical activity may therefore influence cancer risk through several biological pathways at once.
Earlier studies have linked higher activity with reduced risk of cancers including breast, bowel, kidney, bladder and stomach cancer. The UCL study does not replace that evidence but adds a new way of thinking about how everyday movement fits into a full day.
The findings also fit with a growing interest in 24-hour movement guidelines. This approach recognizes that health is shaped by a combination of physical activity, sedentary time and sleep rather than by exercise alone.
UK health guidance currently recommends at least 150 minutes of moderate-intensity activity each week or 75 minutes of vigorous activity. Strengthening exercises for the major muscle groups are also recommended on at least two days each week.
Moderate activity includes movement such as brisk walking that raises the heart rate while still allowing a person to talk. Vigorous activity requires more effort and can include jogging, fast cycling and energetic sports.
The new study is strong in several ways. It included tens of thousands of people, followed them for years and used wearable measurements, which can capture daily movement more accurately than memory-based surveys.
But the percentages should be interpreted carefully. The researchers did not randomly assign people to sit for 15 minutes less every day and then observe whether fewer cancers developed.
Instead, they studied existing behavior and used models to estimate associations between different activity patterns. This means the research cannot prove that a specific 15-minute change will produce a precise reduction in cancer risk for every person.
UK Biobank volunteers may also differ from the general population, and cancer is influenced by many factors including age, genes, smoking, alcohol, diet, infections and environmental exposures. Physical activity is only one part of that larger picture.
Even so, the findings offer a useful practical idea. Health benefits may come not only from scheduled exercise but also from protecting the movement already present in daily life and replacing some unnecessary sitting with activity.
The most sensible message is therefore not to obsess over an exact number of minutes. It is to keep moving regularly, maintain more demanding activity when it is safe to do so, get adequate sleep and avoid allowing long periods of sitting to take over the day.
Source: University College London.
