Share on PinterestPhysical activity is linked to a reduced risk of many cancers. Vlad Georgescu/Getty Images
- Physical activity may reduce the risk of many types of cancer, while inactivity appears to increase the risk.
- However, the time of day people exercise may also influence that risk.
- A study indicates that being active in both the early morning and evening might provide greater benefits than overall activity in reducing colorectal cancer risk.
- The researchers suggest their findings could help shape cancer-prevention programs.
Regular physical activity improves overall health, and can help prevent many health conditions. However, according to the Centers for Disease Control and Prevention (CDC), less than a quarter of adults in the United States met the recommended guidelines for both aerobic and muscle-strengthening activities. And the number of people meeting the guidelines declined with age.
Cancer risk, which increases with age, could also be affected by physical activity levels. There is strong evidence that higher levels of physical activity reduce the risk of bladder, breast, colon, endometrial, oesophageal and stomach cancers, and some evidence that it may lower the risk of lung, ovarian, pancreatic, renal, and prostate cancers.
For example, a large study found higher levels of exercise—equivalent to 2.5-5 hours of moderate-intensity activity, such as brisk walking per week—were associated with a lower risk of many different cancers, including liver cancer, colon cancer in men, and breast cancer in women.
So, greater physical activity overall may reduce cancer risk, but could the time of day you exercise have a significant effect?
A new study, using data from the UK Biobank, suggests that exercising in the morning and evening may reduce the risk of colorectal cancer more than overall activity.
The study, led by experts from the University of Regensburg, Germany, is published in BMC Medicine.
“It is a well-known fact that exercise has an anti-inflammatory effect which may reduce the risk of developing colorectal cancer. Little, however, is known about the timing of exercise and whether diurnal variations impact colorectal cancer risk. This study uses novel methodology which has both strengths and limitations. While it provides a better understanding of variations in time it does not capture many other aspects of exercise – intensity, type (aerobic vs anerobic) or the history of previous physical activity in these individuals.”
— Anton Bilchik, MD, PhD, surgical oncologist, chief of medicine and Director of the Gastrointestinal and Hepatobiliary Program at Providence Saint John’s Cancer Institute in Santa Monica, CA.
24-hour activity tracking identified exercise patterns
The researchers used 24-hour tracking of 86,252 people aged 42-79 years from the UK Biobank. All participants wore a wrist-worn triaxial accelerometer on their dominant wrist continuously for 7 days. After 7 days, they returned the device to the coordinating center for analysis.
From this, the researchers identified 4 types of activity pattern:
- Continuous day-long activity
- Late-day activity
- Early plus late-day activity
- Mid-day plus night-time activity
They followed up with participants for a median of 5.3 years, until whichever came first of cancer diagnosis, loss to follow-up, death, or complete follow-up. They focused on colorectal cancer, as this has the strongest evidence of an inverse relationship to physical activity.
Higher activity decreased bowel cancer risk
Activity patterns were associated with how healthy the participants’ overall lifestyle was. Those in group 3 (morning and evening activity) had the healthiest lifestyles, characterized by higher overall acceleration, decreased alcohol drinking and smoking habits, and lower sedentary behavior. Next came those in group 1, then 2 and 3.
In general, physical activity throughout the day was associated with decreased risk of colorectal cancer, with a continuous day-long activity pattern showing a 6% reduction in risk.
A late-day activity pattern was suggestively associated with a 7% reduction in risk. The early plus late-day activity group showed an 11% decrease in risk—more than any other activity pattern.
Finally, a mid-day plus nighttime activity pattern showed no statistically significant change in risk.
“The study makes good observations and potentially touches on a new way to reduce the incidence of bowel cancer,” Nilesh Vora, MD, board certified hematologist and medical oncologist and medical director of the MemorialCare Todd Cancer Institute at Long Beach Medical Center in Long Beach, CA, told Medical News Today.
“We may have uncovered a way to reduce the risk of colon cancer and that is always exciting given the rising number of cases we are seeing in patients under 50,” he added.
Although there are few studies into the effect of physical activity timing on cancer risk, some studies have investigated whether time of exercise has health impacts. One study found that, for older adults, moderate to vigorous activity at any time of day lowered all-cause mortality (including cancers). Exercise taken from midday to the early afternoon or at mixed times had more impact than exercise taken only in the morning or evening.
Another wide-ranging review of studies found no consistent evidence that exercising at any particular time of day had a greater impact on health risks.
“This study finds a possible link between exercising early and late in the day and lower risk of bowel cancer. However we need more, bigger studies with longer follow up to confirm whether the time of day that we exercise has an impact on bowel cancer risk.”
— Maxine Lenza, health information manager at Cancer Research UK.
Why might morning and evening exercise have this effect?
This study found that the benefits of early morning and evening activity were greater than the benefits of overall physical activity. The authors suggest this may be because it means that people have more active time during the day.
This suggestion is supported by evidence from a previous UK Biobank study that observed a reduced cancer risk in people who exercised morning and evening, and that this activity pattern was linked to lower levels of inflammation, which may have mediated the reduced cancer risk.
Bilchik added to this potential explanation:
“There are diurnal changes in our metabolism which may reduce the risk of developing colorectal cancer through a variety of mechanisms including changes in insulin metabolism and inflammation. This may provide opportunities to further evaluate mechanisms for colorectal cancer prevention as well as whether treatments in patients with colorectal cancer are more likely to be effective during these times.”
Advice for reducing colorectal cancer risk
Lenza advised: “Being physically active helps with maintaining a healthy weight, which reduces the risk of 13 types of cancer, including bowel cancer. Anything that gets you a bit warmer, slightly out of breath, and your heart beating faster counts.”
She pointed out other potential “ways to reduce your risk of bowel cancer include stopping smoking, eating a healthy balanced diet with lots of fruit and veg and less processed and red meat, and cutting down on alcohol.”
Bilchik echoed these comments:
“I think it is too early to advise individuals to change their exercise schedules to twice a day, but this study does emphasize the importance of physical activity and exercise to reduce the risk of developing colorectal cancer.”
