- Exercising at specific times of day could lower colorectal cancer risk, a new study found.
- Activity is known to reduce cancer risk, but how timing affects this isn't well-studied.
- Colorectal cancer rates have fallen since the '80s, but have risen in under-55s by 1 to 2% yearly since the mid-'90s.
Being physically active in both the morning and evening could reduce the risk of colorectal cancer by 11%, according to a new study.
Previous studies have found that people who exercise regularly have a lower colorectal cancer risk than those who don't. This latest research, published September 18 in the journal BMC Medicine, suggests that what time of day someone is active could have an impact too.
Professor Michael Leitzmann, lead author of the study and chair of the department of epidemiology and preventive medicine at the University of Regensburg, Germany, told Business Insider that the findings could be a helpful jumping-off point for research into new colorectal cancer prevention strategies.
But he stressed that from a public health perspective, people should be encouraged to be active at any time of the day.
Sam Orange, a senior lecturer in clinical exercise physiology at the University of Newcastle, UK, who has studied the impact of exercise on colorectal cancer prevention and was not involved in the study, told BI that the findings could help create more accurate and clearly-defined physical activity guidelines for cancer prevention.
Leitzmann and his team analyzed the physical activity habits of 86,252 participants aged between 42 and 79 who shared their health and lifestyle information with the UK Biobank biomedical database. They were asked to track their activity by wearing a device on their wrist known as an accelerometer.
After five years, 529 of the participants were diagnosed with colorectal cancer, also known as bowel cancer.
People who were active in the morning and evening had an 11% lower risk of developing bowel cancer
The researchers identified four common patterns of activity: continuous daylong activity, activity late in the day, activity in the morning and evening, and activity at midday and at night.
The primary finding was that two peaks of activity, one around 8 a.m. and the other around 6 p.m., was associated with a lower colorectal cancer risk "beyond the benefits of overall physical activity," the authors said.
Daylong activity was associated with a 6% lower risk, and middle of the day and the night activity didn't appear to impact the participants' risk. Data from those who were only active later in the day was inconclusive.
Further research is needed to confirm whether the time we exercise affects our colorectal cancer risk, but Leitzmann suspects it stems from beneficial biological processes being activated twice a day instead of once.
In 2022, Orange's research group found in a study published in the International Journal of Cancer that each exercise bout releases of cancer-fighting molecules into the bloodstream, which is thought to help reduce tumor growth. They used colon cancer cells and blood samples from 16 men over 50 who, due to lifestyle choices, had a higher risk of colon cancer.
"Therefore, being active twice daily, instead of once, could provide additional benefits by allowing more cancer-fighting molecules to be released into the bloodstream," he said.
More people under 55 are developing colon cancer
Colorectal cancer is the third-leading cause of cancer-related deaths in US men and the fourth-leading cause in US women, according to The American Cancer Society. It's expected to cause about 53,010 deaths this year.
The rate of people being diagnosed with the condition has fallen since the mid-1980s, but in people under 55, rates have been increasing by 1% to 2% a year since the mid-1990s, the Society said.
Experts still don't know what's behind this uptick, but many potential explanations, including ultra-processed foods, microplastics, and obesity, are being studied.
Dr. Michael Shusterman, a gastrointestinal medical oncologist at NYU Langone's Perlmutter Cancer Center on Long Island, previously told BI that he typically recommends patients quit smoking; cut down on alcohol; do some moderate-intensity exercise; eat more fiber and less red meat; and avoid ultra-processed foods as much as possible to prevent colorectal cancer.
"Every movement counts for reducing colorectal cancer risk, meaning that doing any amount of physical activity is better than none," Orange said.