Jet lag would promote the growth of tumor cells

When we take the plane for long distances, we happen to be out of phase on landing: it is the jet lag. This phenomenon of lag also affects people working at night, we then speak of social jet lag. In both cases, this situation can be harmful to our body. In addition to the fatigue that sets in and forces us to adjust to another rhythm, jet lag also disturbs our cells. This is the conclusion reached by scientists from the National University of Quilmes (Argentina) and Virginia Tech University (USA). In their study published on October 14, 2020 in the journal Science Advancesscientists talk about the negative effects of jet lag, including its propensity to let tumor cells grow during this period.

The importance of the circadian cycle for the body

Fast travel over very long distances and night work have in common that they do not respect our circadian cycle. The day-night rhythm, on which we are built, allows our body to distinguish when it must be active (during the day) from when it must rest (at night). The rest and sleep phases are important because it is when we reset all our functions, whether it is to store energy, rest our brain or strengthen our immune defenses.

By ignoring the circadian cycle, we stress our immune defenses. Each cell in our body has its own molecular clock, which it adjusts when certain functions of our body are at rest. The brain is the master of our body’s time, which uses daylight to synchronize all the peripheral clocks of our cells.

In cancer cells, this molecular clock is disrupted, which explains this anarchic, rapid and uncontrolled development. When the perception of day and night becomes confused, our brain no longer knows how to determine for our cells the right moment for them to rest. With this confusion, they put themselves in a state of stress, which reduces their effectiveness. It is during this phase that cancerous cells can grow.

Cancer cells take advantage of chronic stress from healthy cells

To carry out their research, the scientists examined two groups of mice. The first was subjected to a strict circadian rhythm with twelve hours of light and twelve hours of darkness. The second group saw their ranges of light and shadow shifted by six hours every two days, which is equivalent to crossing 21 different time zones in a week.

After a month, the researchers noticed that the tumors in the mice subjected to jet lag had tumors three times larger than those in the control group.

“One of the key takeaways from this study is that if someone has a proliferative disorder, in this case melanoma, shifting work or changing time zones on a regular basis could exacerbate the problem by hampering response immune system to tumor growthsays Carla Finkielstein, associate professor of biology at the Faculty of Science at Virginia Tech and director of the molecular diagnostic laboratory at the Fralin Biomedical Research Institute (USA). This research also helps explain why some tumors gain ground when a person is exposed to the chronic stressful conditions that occur when their environment and biological clock are out of sync.“

Immune defenses lose effectiveness

At the microbiological level, jet lag weakens the immune defenses, this is what scientists have noticed in mice. With a staggered rhythm, they realized that macrophages, these white blood cells responsible for eating and destroying cells and failing, are much more inclined to let tumor cells proliferate.

“We combined two different approaches to chronobiology research to study the effects of circadian desynchronization on tumor growth and immune rhythms, and found a linkdescribes Diego Golombek, professor at the National University of Quilmes. It takes optimal rhythms in immune cells and immune humoral factors to stifle rapid tumor growth. When circadian rhythms are chronically disrupted, these rhythms are altered, reversed, or disappear altogether, which could help explain why tumors were much larger in the desynchronized group..”

Diego Golombek and Carla Finkielstein plan to expand their research on the immune system and cell cycles, this time focusing on cancer.