Why Exercise Lowers Cancer Risk: An Oncologist’s Perspective

Regular physical activity is linked to a lower risk of developing several types of cancer. Data from the National Cancer Institute released on March 26, 2025, indicates that individuals with the highest total amount of daily physical activity had a 26% lower risk of developing cancer than those with the lowest levels of activity.

The Centers for Disease Control and Prevention stated on February 9, 2026, that being physically active lowers the risk for at least eight specific types of cancer. These include cancers of the bladder, breast, colon, endometrium, esophagus, kidney, lung and stomach.

Defining Physical Activity and Intensity

Physical activity is defined as any movement that uses skeletal muscles and requires more energy than resting. This includes a wide range of activities such as walking, running, dancing, biking, swimming, exercising, engaging in sports, and performing household chores.

Medical researchers use a measure called the metabolic equivalent of task, or MET, to characterize the intensity of these activities. One MET represents the rate of energy expended by a person sitting at rest.

Physical activity is categorized by MET levels as follows:

• Light-intensity activities: Expend less than 3 METs.
• Moderate-intensity activities: Expend 3 to 6 METs.
• Vigorous activities: Expend 6 or more METs.

Sedentary Behavior and Cancer Risk

Sedentary behavior is defined as any waking behavior characterized by an energy expenditure of 1.5 or fewer METs while reclining, sitting, or lying down. Common examples include driving a vehicle, most office work, and sitting while watching television.

The National Cancer Institute notes that it is possible for a person to be physically active and yet still spend a substantial amount of time being sedentary.

Evidence linking higher physical activity to lower cancer risk is primarily derived from observational studies. While these studies cannot prove a causal relationship, the National Cancer Institute states that evidence of a causal connection is provided when studies in different populations show similar results and a possible mechanism for that relationship exists.

Specific Findings and Clinical Perspectives

Some research has highlighted specific risk reductions for certain cancers. In a 2014 meta-analysis involving 11 cohort studies and 4 case-control studies, the risk of bladder cancer was 15% lower for individuals with the highest level of occupational or recreational physical activity compared to those with the lowest level.

Beyond prevention, medical professionals also recognize the value of exercise for those already diagnosed. A Canadian National Survey revealed that most oncologists believe exercise during cancer treatment is beneficial.