The title of a 2019 paper published in the Journal of Physiology got my attention: “Acute High Intensity Interval Exercise Reduces Colon Cancer Cell Growth”[i]. Questions immediately popped into my mind:
- “Acute” implies a short-term burst of activity. How short is “acute”?
- How intense is “high”?
- How long are the intervals?
- How can a burst of high intensity exercise reduce cancer cells?
I dove right in, hoping to find the answers to my questions.
What the article said
The article opens by citing studies showing that exercise lowers colorectal cancer mortality rates. Fair enough—we already know that exercise has many longevity benefits such as increasing heart health, extending life for advanced prostate cancer patients, and even preventing prostate cancer altogether. The authors then identify a number of current theories about the biological mechanisms that affect colorectal cancer cells, including the release of cytokines. More about cytokines in a bit.
The study involved 20 male colorectal survivors age 40+ years. They were assigned to one of two groups:
- Ten performed a single intense 38-minute highly intense exercise session (10-minute warm-up, then four 4-minute periods of intense stationary bike-ride riding separated by 3-minute rests). Blood was drawn before exercise, 0 minutes after exercise, and finally at 2 hours after exercise.
- The other ten were trained to perform the above workout three times per week for 4 weeks. Blood was drawn a few days before starting the 4-week program, and after completion.
All blood samples were processed for a complex biochemical analysis.
In addition, colorectal cancer cells in petri dishes were exposed to fluid from
each blood draw, and the number of cells per dish were counted at certain intervals
over the next 72 hours. Results were as follows:
|Group||Blood Analysis||Effect on cancer cells in dish|
|Single 38-minute intense exercise||0 minutes post-exercise blood samples showed increase in inflammatory cytokines which then abated at 2 hours||Blood samples taken at 0 minutes post-exercise reduced the number of petri dish colorectal cancer cells during the 72-hour counting period. However, blood samples taken at 2 hours post-exercise had no effect on the number of petri dish cancer cells|
|4-week program (workout 3x/week for 4 weeks)||No change observed in cytokines after the 4-week training program||Blood samples taken at the end of the 4-week program had no effect on the number of petri dish cancer cells|
In short, the men who did a single high-intensity workout had an immediate post-exercise increase of inflammatory biomarkers (cytokines) in their blood. When a small amount of this biomarker-loaded blood was placed in a petri dish with colorectal cancer cells, over the next 72 hours the number of cells decreased. However, blood taken from the same men two hours post-exercise quickly returned to baseline biomarker levels that had no effect on the cancer cells. Also, blood taken from men in the training period group also revealed baseline biomarker levels which had no effect on cancer cells. It thus seems that the immediate post-exercise cytokine surge that harms cancer cells disappears quickly.
Cytokines are molecules secreted by immune system cells, and they act as biochemical instruction manuals between cells. Healthy cells generate cytokines but so do cancer cells. There are many different cytokines such as growth factors, interferon, interleukin, etc. Some cytokines are inflammatory while others are anti-inflammatory. When an injury or invasion of the body occurs, a natural response of the immune system uses cytokines to generate an inflammatory response that can help protect and assist tissue during wound healing or help eliminate invaders. So, inflammation is a good thing, right?
Not necessarily. Chronic inflammation sets in if it persists after the need for it is over. It can become a precursor for prostate cancer and other cancers. Furthermore, tumor cells can also produce inflammatory cytokines as a sort of survival strategy following radiation or chemotherapy, often defeating the treatment’s effectiveness. This raises the question: is inflammation good or bad? And if it’s bad, why should anyone exercise vigorously if inflammatory cytokines might encourage cancer?
Those questions are addressed in another research article I found, “A Model for Cancer-Suppressive Inflammation.” [ii] The authors point out that blaming cancer on inflammation is a “misleading oversimplification.” In animal experiments, they found that certain type of immune system T-cells mount an antitumor response that includes pro-inflammatory cytokines. They cite other published evidence that the increased number of T-cells and other immune system components at a tumor site—in other words, inflammation—generates a lethal infiltration into cancer cells that may discourage proliferation or even cause cancer cells to die off.
To inflame or not to inflame?
To return to the exercise study, the authors themselves note that the role of inflammatory cytokines “is somewhat perplexing given that chronic inflammation… is a hallmark of cancer and is associated with an increased risk of incidence…”[iii] They add a technical discussion of mechanisms by which both the immune system and cancer cells employ cytokines, and admit that their study can’t rule out additional as-yet-unknown biochemical factors to account for the drop in petri dish cancer cells. They conclude, however, that given how short-lived the increased cytokine response is after intense exercise intervals, people should embrace a regular practice of vigorous exercise as a way to regularly engage Nature’s own anti-cancer powers through the immune system. In other words, get thee to a gym!
NOTE: This content is solely for purposes of information and
does not substitute for diagnostic or medical advice. Talk to your doctor if
you are experiencing pelvic pain, or have any other health concerns or
questions of a personal medical nature.
[i] Haabeth OA, Bogen B, Corthay A. A model for cancer-suppressive inflammation. Oncoimmunology. 2012 Oct 1;1(7):1146-1155.
[ii] Devin JL, Hill MM, Mourtzakis M, Quadrilater J et al. Acute high intensity interval exercise reduces colon cancer cell growth. J Physiol. 2019 Apr;597(8):2177-2184.
[iii] Devin et al., ibid.