Jet lag affects metabolism in ways that might surprise you—new research from Kyushu University reveals that the impact of chronic jet lag on metabolism is not one-size-fits-all.
In a series of eye-opening experiments, scientists discovered that while male mice pack on extra weight and struggle with glucose intolerance under relentless time-zone shifts, their female counterparts actually shed pounds.
Yes, you read that right—what messes up one sex can slim down the other.
For those who’ve ever felt the soul-sapping drag of long-haul flights or the groggy misery of shift work, this study offers a fresh twist.
It appears that jet lag affects metabolism in distinctly gender-specific ways. Researchers set out to decode this biological conundrum by subjecting mice to regular shifts in their light-dark cycles—mimicking the chronic jet lag we so often experience.
“Chronic jet lag, where a person’s body clock is consistently out of sync with natural day-night cycles, is a condition that affects many people, such as shift workers,” says senior author Professor Shinobu Yasuo from Kyushu University’s Faculty of Agriculture.
With this stark reminder, the study took a hard look at how frequently disrupted circadian rhythms can lead to metabolic mayhem.
Under controlled conditions, the researchers tweaked the mice’s schedules by advancing the room lights by six hours every two days—quite the rude awakening for these critters compared to the predictable 12-hour cycle enjoyed by the controls.
Over an eight-week period, the differences became undeniable: male mice under chronic jet lag conditions not only gained weight but also developed glucose intolerance—a precursor to diabetes. Meanwhile, female mice defied expectations by losing weight.
“The biggest issue so far is that animal studies have typically focused only on males, yet over half of all shift workers, such as nurses, are women,” says Yasuo.
It was this glaring oversight that prompted the team to include female mice in their experiments, ultimately revealing a surprising divergence in how each sex responds to the stress of a constantly shifting body clock.
To dig deeper into the mechanics behind these differences, the researchers examined the activity of clock genes in the liver and adrenal glands, along with tracking the mice’s deep body temperature—a reliable marker of their internal rhythms.
The findings were as clear as day: female mice experienced a far greater disruption in both gene activity and body temperature patterns, whereas male mice’s internal clocks seemed more stubbornly resilient.
In a further twist, when male mice were castrated and then subjected to the same jet lag conditions, their responses shifted dramatically.
These males began mirroring the females, showing perturbed body temperature and clock gene activity, coupled with weight loss. “Testosterone is therefore key to a resilient body clock in male mice. It also significantly impacts metabolism and how the body responds to glucose,” says Yasuo.
The study not only deepens our understanding of how jet lag affects metabolism but also raises intriguing questions about the role of sex hormones.
Future research will aim to unravel why male mice tend to gain weight despite minimal changes in their clock genes and how estrogen might protect or impair the female body clock.
The observed weight loss in female mice even challenges the common perception that jet lag invariably leads to weight gain.
“It could be that jet-lagged female mice are more sensitive to stress and anxiety,” suggests Yasuo, hinting at a complex interplay between stress responses, appetite, and metabolic regulation.
“Of course, human lifestyles are much more complicated. Different people respond to stress in different ways, or have different dietary or exercise habits,” he continues.
Yet, the overarching message remains clear: understanding these gender differences is essential for crafting better health strategies for anyone whose life is dictated by irregular hours.
In essence, this research invites us to reconsider our approach to managing jet lag and its ripple effects on our health. It’s not just about the fatigue; it’s about the intricate dance of hormones, metabolism, and the ever-elusive body clock—a dance that plays out very differently for men and women.
For more information about this research, see “Sex-dependent effects of chronic jet lag on circadian rhythm and metabolism in mice” Tiantian Ma, Ryohei Matsuo, Kaito Kurogi, Shunsuke Miyamoto, Tatsumi Morita, Marina Shinozuka, Fuka Taniguchi, Keisuke Ikegami & Shinobu Yasuo, Biology of Sex Differences, https://doi.org/10.1186/s13293-024-00679-z
