Jet lag and shift work don’t just make you tired; they also damage your body and brain.

Disruption of the body’s circadian rhythms is common due to jet lag and rotating work hours, and the new study from the University of Massachusetts Amherst pinpoints the underlying reason for the negative health impacts.

The study, which was published in the journal eNeuro, also demonstrates that adult neurogenesis, or the continual production of new neurons in the hippocampus of the brain, is regulated by the circadian clock gene Cryptochrome 1 (Cry 1). Adult neurogenesis is essential for learning and memory, and problems with this process have been associated with dementia and other mental illnesses.

Lead author Michael Seifu Bahiru, a Ph.D. candidate working in the lab of Eric Bittman, Professor Emeritus of Biology, says that “Circadian disruption impacts a lot of things.”

“There are links to cancer, diabetes and hypertension, as well as adverse impacts on neurogenesis.”

The circadian clock regulates cell birth and survival in the adult hippocampus, and disrupting it can affect neurogenesis. In the United States, approximately 30 million individuals undergo phase shifts in their circadian rhythms due to rotating work schedules.

For a while, researchers were uncertain about the cause-and-effect relationship between circadian disruption and its associated health problems. Bahiru explains that they pondered whether the problem stemmed from the act of shifting or the shift itself.

According to Bittman, altering the light cycle may be the root cause of the negative impact on neurogenesis. He suggests that shifting the circadian clock abruptly is harmful, as opposed to the time delay associated with jet lag, which is the period required for all the body’s circadian-dependent systems to adapt to changes in daylight.

The study’s results confirm the theory that jet lag causes an internal misalignment, resulting in desynchrony among organs and systems, including neurogenesis. The researchers believe that circadian disruption could also have other harmful health consequences.

The researchers investigated their theory by examining cell birth and differentiation in Syrian hamsters. They focused on hamsters with a recessive mutation in the Cry 1 gene, which quickens the circadian clock in steady circumstances and greatly enhances its capacity to respond to light-induced shifts. Bittman called this mutation “duper,” which was discovered in previous studies. Additionally, a control group of hamsters without the duper mutation was examined, and both groups experienced similar changes in the light cycle.

The researchers replicated jet lag conditions by imposing eight-hour forward and backward shifts at eight 16-day intervals. During the experiment’s midpoint, a cell birth marker was administered. The findings revealed that jet lag has minimal impact on cell birth but alters the development of newborn cells, causing them to veer away from becoming neurons. However, the “duper” hamsters were immune to this phase shift effect.

“As predicted,” adds Bahiju, “the duper animals re-entrained quicker, but also were resistant to the negative effects of the jet lag protocol, whereas the control – the wild type hamsters – had reduced neurogenesis.”

The findings concluded that “circadian misalignment is critical in jet lag.”

Bittman’s laboratory aims to increase comprehension of the mechanisms involved in human circadian rhythms, which could lead to the prevention or treatment of the effects of shift work, jet lag, and circadian rhythm disturbances. This new study is a step forward in achieving that goal.

Now the team will turn to “a big unanswered question,” Bittman adds – “whether it’s the operation of circadian clocks in the hippocampus that is being directly regulated by shifts of the light: dark cycle, or whether neurogenesis is controlled by biological clocks running in cells elsewhere in the body.”

Bittman believes that another option, which is more plausible, is that the suprachiasmatic nucleus in the hypothalamus, which serves as the master pacemaker, detects the light shift and transmits the signal to the stem cell population that is responsible for dividing and differentiating in the hippocampus.

Image Credit: Richard Baker / In Pictures via Getty Images Images