There is a plethora of data that shows exercise prevents Cancer. In fact, many types of Cancer are reduced by exercise including:

• Breast Cancer
• Stomach Cancer
• Colon Cancer
• Bladder Cancer
• Esophageal Cancer
• Kidney Cancer
• and more…

Based on most of the data, people with the highest levels of exercise tend to see a decrease of Cancer risk by at least 20%.

While it seems pretty clear that exercise is beneficial for Cancer, what hasn’t been clear is how it does this. A new paper sheds a little bit of light on how exercise slows the development of Cancer.

The interesting thing about this is that this same mechanism may also protect us from infections, including COVID-19.

Energy metabolism during exercise

One of the more profound ways that exercise changes our physiology is through alterations in energy metabolism. When we go from sedentary to exercise, there is a substantial increase in our energy metabolism based on the volume and intensity of exercise.

At low exercise intensities such as walking, we generate energy primarily through the metabolism of fat. As exercise intensity increases to jogging and running, we transition towards using more glucose to create energy.

One byproduct of increased energy metabolism from glucose is lactate. Once believed to be a simple waste product of metabolism, it’s now clear that lactate is not only an energy source, but a signaling molecule.

Higher exercise intensities require rapid energy, which increases lactate production. Fast twitch muscle fibers generate most of the lactate, but metabolize it poorly. So fast twitch muscle fibers eject lactate towards one of 2 fates.

First, local slow twitch muscle fibers metabolize lactate well, so they suck it up. Additionally, other tissues such as the brain and gut use lactate as well.

Conversely lactate enters the blood and travels to the the liver. The liver then converts lactate into glucose via the Cori Cycle and sends it back into the blood to further power energy metabolism during exercise.

How exercise prevents Cancer

This increase in blood lactate appears to be central in how exercise helps kill and limit the spread of cancerous cells. As we produce more lactate during exercise, it enters the blood and alters the activity of immune cells.

A particular set of immune cells called cytotoxic T cells become more effective at removing cancer cells in those who exercise. As the name suggests, cytotoxic T cells are T cells that kill cells(Cyto=cell, toxic=killing).

Of course, we don’t want to kill just any type of cell. Cytotoxic T cells recognize abnormal cells such as those with mutated DNA or infected by viruses. When they encounter these cells, they kill them, leaving healthy cells alone.

In a recently published paper, researchers found that cytotoxic T cells are more effective at removing Cancer cells in mice that exercise. In untrained mice, transplanting cytotoxic T cells from exercising mice reduced their tumor burden.

Finally, infusing mice with sodium lactate also decreased tumor burden in mice, but not to the same extent as exercise. This indicates that other metabolites from exercise energy metabolism, along with lactate, prime cytotoxic T cells to eliminate cancer cells.

Though this study didn’t look at virally infected cells, exercise does appear to have a beneficial effect on preventing viral infections. Thus, this same mechanisms may hold true for preventing viral infections such as SARS-CoV2.

You may have heard of cytotoxic T cells, also called killer T cells, recently. Cytotoxic T cells are important for determining the severity of COVID-19 illness. Poor cytotoxic T cell responses lead to poorer outcomes. For a video on the basics of viral immunity, click here.

Conclusion

The benefits of exercise extend across many domains of human health. If exercise were a pharmaceutical drug, it would be the most widely prescribed drug in the World.

Evidence indicates that exercise prevents Cancer, but how does it do it? We know that exercise decreases inflammation, but is there something else about exercise that prevents Cancer?

As it turns out, metabolites generated during exercise act as signaling molecules that change the way many types of cells in our body function. Lactate is one of these molecules that was largely believed to be just waste for a long period of time.

Through the generation of systemic lactate, exercise helps prime cytotoxic T cells to become more efficient killers of cancerous cells. Since cytotoxic T cells are also important for controlling viral infections, this same mechanism may play an important role in preventing infection with SARS-CoV2, or to reduce the risk of severe illness leading to COVID-19.