December 14, 2021 | 4 minute read

If you are familiar with AICR’s Cancer Prevention Recommendations, you likely know that exercise is one of the key steps for lower cancer risk. Now comes a major study that estimates three percent of all U.S. cancer cases annually—approximately 46,000 cases—could be prevented if inactive adults were to meet the physical activity guidelines of five hours per week.

The study was published in Medicine & Science in Sports & Exercise.

It is the first study to estimate the number of cancer cases attributable to physical inactivity based on cancer sites for each state, placing a concrete figure on the strong research involving exercise and cancer.

Being physically active, a clear link to lower cancer risk

AICR’s comprehensive analysis of the global research concluded that regular physical activity lowers the risk of breast, colorectal and endometrial cancers. There were also indications that physical activity may lower risk of esophageal, liver and lung cancers, but the evidence was not strong enough to meet AICR’s rigorous guidelines to conclude a clear link.

Single studies over the years have found physical activity lowers the risk of several cancers beyond what AICR has concluded, such as this one. The research involving exercise and cancer also points to many benefits of physical activity for survivors.

Both laboratory and clinical studies show that physical activity spurs numerous health benefits, including supporting the immune system, reducing chronic inflammation and promoting healthy levels of hormones like insulin and estrogen. All of these factors play a role in many of the most common cancers.

AICR recommends meeting the U.S. government recommendations for physical activity: 30 to 60 minutes of moderate-intensity activity per day (2.5 to 5 hours per week), or at least 75 minutes per week of vigorous exercise.  All activities that raise your heart rate to at least a moderate activity count, including brisk walking, dancing and swimming.

Calculating the cancer-inactivity risk

For this study, researchers first gathered data on cancer incidence and activity habits of residents ages 30 and over in each state and the District of Columbia. They pulled activity data from self-reported surveys from 2013 to 2016.

The authors broke people’s activity habits into eight categories depending upon the energy expended, with the lowest being 0—completely inactive. The highest category was equivalent to five hours of moderate-intensity activity per week, or 45 minutes per day.

For their calculations, the researchers focused on total cancer incidence and seven cancer types drawn from an analysis of nine studies. This analysis found specific lower risk when comparing high to low activity levels for cancers of the breast, endometrium, colon, stomach, kidney, esophagus and bladder.

A last step was placing all the figures in an equation called the population attributable fraction. This gives the proportion of incidents (such as cancer) in a population attributed to a specific risk factor (such as inactivity).

Cancers attributed to inactivity

When compared to the highest recommended level of physical activity—five hours a week—the study estimated that 3 percent of all incident cancer cases (excluding nonmelanoma skin cancers) were attributable to physical inactivity. The proportion of cancers due to inactivity was higher in women, with annual cases more than double the numbers of men.

For specific cancer sites, 9.3% of colon cancers, 8.1% of esophageal cancers and 6.5% of female breast cancers were associated with lack of exercise. By state, the proportion of cancer cases attributable to physical inactivity ranged from 2.3% in Utah to 3.7% in Kentucky.

There are many barriers to physical activity, with some more likely to affect historically marginalized populations and individuals with a limited income, note the authors. The findings underscore the importance of interventions, including community programs and appropriate infrastructure, to promote physical activity across states, notably in states with a higher prevalence of physical inactivity and attributable cancer cases, they conclude.

Over 9 hours of daily inactivity, making the move to move

The study estimating preventable cancer cases with exercise was published just before a new paper estimated that the average American adult is far more sedentary than previously believed, spending an average of 9.5 hours of daily waking time inactive. That figure is 34 percent higher than previously estimated.

Conducted by authors at the National Cancer Institute, this study used a new method of collecting inactivity levels, asking participants ages 20 to 75 to recall their sitting time over the previous day. Leisure time accounted for close to half of total sedentary time. For those who are inactive or simply want to move more, here are some tips to get started.

You can also join others working to live healthier lives by signing up for AICR’s online Healthy10 Challenge.

The study estimating cancers attributable to inactivity was supported by the American Cancer Society.