Optimal Physical Activity for Preventing Digestive System Cancers

Digestive system cancers (DSCs), including malignancies of the esophagus, stomach, colon, rectum, pancreas, liver and other digestive organs account for nearly one-third of global cancer incidence and 40% of cancer-related deaths. Despite their heavy burden, prevention strategies remain limited.

While obesity, smoking, alcohol and diet are well-established risk factors, physical activity has emerged as a promising protective factor. New research from JAMA Oncology relied on decades of data from major U.S. cohorts, suggested that when it comes to preventing DSCs, maintaining consistent, moderate physical activity is more effective than intermittent periods of high-intensity effort.

Yiwen Zhang, Ph.D., from the Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, and colleagues addressed this gap by examining both the amount and long-term consistency of physical activity in relation to DSC risk and mortality. Their findings provide compelling evidence that steady, moderate activity over decades may be the most effective strategy for prevention.

The investigators pooled data from three of the largest and longest-running U.S. prospective cohorts: the Health Professionals Follow-Up Study, the Nurses’ Health Study, and the Nurses’ Health Study II. These cohorts included 231,067 men and women who were free of cancer and cardiovascular disease at baseline. Participants were followed for up to 32 years (1988–2021) with biennial questionnaires capturing lifestyle, medical history and detailed physical activity patterns.

Physical activity was quantified in metabolic equivalent task (MET) hours per week, a standardized measure of energy expenditure. Activities such as walking, running, cycling, swimming and aerobics were included. Importantly, the researchers assessed not only total activity levels but also consistency, defined as the percentage of follow-up years in which participants met the guideline threshold of at least 7.5 MET-hours/week (equivalent to 150 minutes of moderate activity).

The primary outcomes were incidence of digestive system cancers and mortality from these cancers, confirmed through medical records, pathology reports and death registries. Over three decades of follow-up, the study documented 6,538 incident DSC cases and 3,791 DSC deaths.

Several important patterns emerged. The study confirmed a general inverse association, that is, higher total physical activity was associated with lower total DSC risk and mortality. Participants engaging in ≥45 MET-hours/week (roughly 10 hours of brisk walking or 4 hours of running) had a 17% lower risk of DSC (HR, 0.83) and a 28% lower risk of DSC mortality (HR, 0.72) compared with those performing less than 3 MET-hours/week.

There were observed benefits across cancer sites, as protective association was observed for both digestive tract cancers (mouth, esophagus, stomach, colon, rectum) and accessory organ cancers (pancreas, gallbladder, liver).

Traditional dose-response analysis suggested that risk reduction plateaued at about 50 MET-hours/week, beyond which additional activity did not confer further benefit.
Consistency did matter the most when long-term patterns were considered. Individuals who consistently met the guideline at moderate levels (median 17 MET-hours/week, or about 5 hours of brisk walking weekly) had substantial reductions in DSC risk (HR, 0.83). Strikingly, those who consistently performed much higher amounts (median 39 MET-hours/week) did not experience additional benefit.

This study offers some of the most definitive evidence thus far that sustained, moderate physical activity is adequate for excellent protection against malignancies of the digestive system. The results go against the idea that "more is always better" and instead show that consistency is the most important thing.

Results suggest the outcomes can benefit public health. Most adults can reach the best protective threshold of about 17 MET-hours per week by walking briskly for 5 hours or running for 2 hours a week. This is very similar to what the American Cancer Society already says, which makes their suggestions even more relevant and adds some complexity about how important it is to stay active for decades.

The authors suggest that preventative programs should focus on maintaining moderate activity levels instead of promoting excessive exercise routines. They also want more investigation into biological processes that could explain the beneficial effects, such as better insulin sensitivity, less inflammation and better movement in the digestive system.