Working out at these times of day could reduce your risk of colorectal cancer by 11%, new study says

Compared to other workout patterns studied, peak physical activity in both the morning and evening, around 8 a.m. and 6 p.m., was associated with an 11% lower risk of colorectal cancer “beyond the benefits of overall physical activity,” according to research published in September in the journal BMC Medicine.

Researchers from institutions in Germany, France, Canada, and Spain used information from a health research database called the UK Biobank to assess the physical activity habits of more than 86,000 people aged 42 to 79, over half (56%) of whom were women. They wore accelerometers, devices that tracked their physical activity, on their dominant wrists for a week. The researchers noted these activity patterns among study participants: 

1. Continuous daylong activity
2. Activity later in the day (6 p.m.)
3. Early and late-day activity (8 a.m. and 6 p.m.)
4. Activity in the middle of the day and during the night

During the median five-year follow-up period, more than 500 participants (0.6%) developed colorectal cancer. After accounting for other cancer risk factors including smoking, shift work, and family history of colorectal cancer, the research team found that people whose physical activity peaked both early and late in the day had an 11% reduced risk of colorectal cancer.

People who were continuously physically active during the day showed a 6% lower risk. People who were active in the middle of the day and at night didn’t have a reduced risk, and data were inconclusive for those mostly active later in the day.

“Our study highlights that not only is physical activity important for reducing colorectal cancer risk, but the timing of peak activity throughout the day could play a crucial role,” lead study investigator Dr. Michael Leitzmann, chair of the Department of Epidemiology and Preventive Medicine at the University of Regensburg in Germany, said in a WCRF news release. “By identifying specific times—early morning and late day—when physical activity is most beneficial, our findings open new avenues for targeted prevention strategies. 

“If confirmed by future research, this could provide a simple yet impactful way for individuals to further reduce their cancer risk through the timing of their exercise.”

Sedentary people saw most benefit from all-day physical activity

While morning and evening physical activity was most beneficial to study participants overall, continuous daylong activity most effectively reduced colorectal cancer risk among participants who reported more sedentary behavior.

One possible explanation for this finding, the researchers noted, is that the more active subjects were already at a lower risk of developing cancer. Therefore, people who spend most of the day sitting down saw a greater health benefit from becoming more active.

“Being physically active is one of our cancer prevention recommendations, and we know that this cuts cancer risk,” Helen Croker, PhD, WCRF assistant director of research and policy, said in the news release. “These intriguing new findings offer potential for developing more specific recommendations, including patterns and timing of physical activity, for reducing cancer risk. 

“This shows the vital importance of World Cancer Research Fund continuing to support research that expands our knowledge to inform cancer prevention going forward.”

Despite the study’s large sample size, its racial and ethnic diversity is limited; 95% of UK Biobank subjects are white. In addition, this study didn’t consider activity type or intensity. Also, because participants wore accelerometers for only a week, that snapshot in time may not be indicative of their long-term behaviors.

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What counts as physical activity?

The study results aren’t meant to suggest you have to hit the gym hard twice a day to lower your cancer risk. Simply incorporating more movement throughout your day—particularly if you have a job that keeps you sitting at a desk or behind a wheel—may help get you on your way. Swapping the elevator for the stairs, for example, is a start.

Any movement that uses your skeletal muscles and requires more energy than resting is considered physical activity, according to the National Cancer Institute. (Yes, doing household chores counts.) To reduce the risk of chronic diseases including cancer, the Physical Activity Guidelines for Americans, championed by the Department of Health and Human Services, recommends adults do this much exercise weekly:

• 150–300 minutes of moderately intense aerobic activity or 75–150 minutes of vigorous aerobic activity
• 2 days of muscle-strengthening activities
• Older adults should also include balance training

Whether you want to sprinkle in brief walks here and there or take up kickboxing, discuss any mobility concerns you may have with your health care provider before switching up your workout routine.

What’s my risk of getting colorectal cancer?

About one in 23 men and one in 25 women will develop colorectal cancer, according to the American Cancer Society (ACS). The organization lists these among the risk factors for the disease:

• 50+ years old
• Alcohol use
• American Indian, Alaskan Native, African American, or Ashkenazi Jewish ancestry
• Colorectal polyps
• Diet high in red and processed meats
• Gallbladder removal (cholecystectomy)
• Inflammatory bowel disease
• Overweight or obesity
• Smoking
• Type 2 diabetes

More than 53,000 people in the U.S. will die from colorectal cancer this year, the ACS estimates. It’s the third-leading cause of cancer-related deaths in men, fourth in women, and second for both sexes combined. The ACS recommends people at average risk of colorectal cancer start regular screenings at age 45.

For more on colorectal cancer:

• More Millennials and Gen Xers are getting colorectal cancer. Even young adults should watch for these 7 symptoms
• Virtual colonoscopy lets you skip the scope. Here’s what to know about the colorectal cancer screening Mark Cuban says saves time and money
• Katie Couric says too many people think colorectal cancer is a man’s disease. She’s imploring women to get potential lifesaving screenings
• Colorectal cancer cases have tripled in teens—and jumped by 500% in kids. What you need to know