US Government Report: Physical Activity, Inactivity Matters for Cancer Risk

This article appears in the April 18, 2018 issue of AICR's Cancer Research Update.

A major new scientific report set to help shape US government guidelines has concluded there is strong evidence that physical activity lowers the risk of certain cancers for adults.

The 2018 Physical Activity Guidelines Advisory Committee Scientific Report also found, for the first time, that sedentary behavior links to increased risk of cancer.

AICR research shows that being physically active, along with staying a healthy weight and eating well, can prevent close to one third of the most common US cancer cases. Add in not smoking and avoiding sun damage and the estimate of US cancer cases that can be prevented grows to nearly half.

Anne McTiernan, AICR/WCRF Expert Panel Member was also a member of the 2018 Physical Activity Guidelines Advisory Committee.  She says, “We found strong evidence that being physically active decreases risk for many cancers. While the greatest benefit was seen in people who are highly active, protection against cancer was seen at all levels of activity.”

With April recognized as National Cancer Control Month, the report reinforces how daily life choices play a pivotal role in lowering cancer risk and overall health. The findings take on added urgency with a recent survey reporting that over a quarter of Americans are inactive.

McTiernan advises, “You don’t need to become an athlete or spend a lot of money in order to gain the benefits of physical activity. All it takes is a pair of walking shoes and determination to fit physical activity into your life.”

New Research, Sedentary Time and Weight Gain: For the 2018 Scientific Report, a committee of experts conducted a systematic review of the scientific evidence on physical activity, fitness, and health. The report is a follow-up to a scientific report a decade earlier, which led to the 2008 Physical Activity Guidelines for Americans.

The growing number of studies in physical activity and health led to the current committee able to identify several health benefits of physical activity not seen in previous reports. These include:

   1). Lowering excessive weight gain for adults. The 2008 Scientific Report found that activity is associated with modest weight loss and prevention of weight gain following weight loss. The new report adds to this evidence, also finding that activity lowers risk of weight gain and obesity.

That's important for overall health, as well as cancer risk. AICR research shows that staying a healthy weight is important for cancer prevention. Overweight and obesity is a cause of 11 cancers, including colon, postmenopausal breast, and endometrial.

   2). More sedentary time links to greater incidence of certain cancers, along with type 2 diabetes and other chronic diseases. The field of sedentary research is a fast emerging one, and in 2008 there was not enough research for that report to systematically assess its health effects.

The 2018 report found moderate evidence indicating that more time spent sitting and in other sedentary behavior linked to higher risk of endometrial, colon, and lung cancers. There was strong evidence that greater sedentary time links to higher risk of cardiovascular disease and type 2 diabetes. Type 2 diabetes shares many cancer risk factors and evidence links having this disease with increased risk of several cancers.

Activity Translates to Lower Cancer Risk: Evidence linking physical activity to lower cancer risk has also grown since the report a decade earlier. This 2018 Scientific Report, which included AICR/WCRF research, included hundreds of epidemiological studies with several million study participants.

The expert committee found strong evidence linking highest versus lowest physical activity levels to reduced risks of breast, colon, endometrial, and several other cancers. Risk reductions ranged from approximately 10 to 20 percent.

There are several possible ways in which physical activity may act to lower cancer risk and, as the report points out, this is a critical area of research. Regular activity can help regulate body levels of insulin and other hormones that increase cancer risk at high levels. Being active may also decrease chronic inflammation. AICR recommends at least 30 minutes of moderate intensity physical activity daily for lower cancer risk.

Over 80 Million Americans Inactive: The new report, supporting AICR research, highlights the importance of both activity and avoiding inactivity to reduce risk of cancers as well as other chronic diseases. Yet a recent survey shows that over a quarter of Americans are currently inactive.

The 2018 Physical Activity Council Participation Report on sports and activities found that 28 percent of the US population – 82.4 million people – are inactive. Over half of the active Americans reported they were active only three times a week at the most.

This rate of inactivity has remained stable for more than five years, with the number of inactive people increasing due to a rising population. When segmented by ages, Americans of all age ranges have slightly decreased their inactivity levels, except for men and women ages 65 and older. Inactivity rates among Americans 65 plus have increased almost 2 percent, with over 40 percent inactive overall.

According to the non-active participants, the top ways to spur them into activity is to have someone there to join in the activity. “Having someone to take part with” and “Having a friend take me along” were the top answers given to get a non-active person involved.

The survey was conducted by the Physical Activity Council, an organization made up of eight industry organizations.

Surveys by other organization have also reported on a troubling level of activity in the United States. According to a State of Obesity report, for example, 80 percent of American adults do not meet the government's  physical activity recommendations for aerobic activity and muscle strengthening. Almost half are not active enough to achieve health benefits.

Read more about the current and upcoming guidelines from the Office of Disease Prevention and Health Promotion.