Disruption to the circadian rhythm can cause weight gain, study says

Disruption to our internal clock, regulated by what's known as the circadian rhythm, may result in weight gain, according to a new study.

The circadian rhythm is a 24-hour cycle controlled by the rise and fall of various hormones in the body. One such hormone, glucocorticoid, peaks at 8 a.m., resulting in a “signal for waking us up and making us bright-eyed and bushy-tailed,” Dr. Mary Teruel, an author on the study and a professor working in the chemical and systems biology department at Stanford University, said in a press release.

But the circadian rhythm can also be influenced by glucocorticoids released into our bloodstream through other means -- from medications, and stress, either physical or emotional.

Stanford researchers wondered whether disruption to the circadian rhythm by glucocorticoids could cause weight gain. So, using mice, researchers looked for connections between weight gain and disruption to our internal clock. Mice were implanted with a bead that would release a low, continuous dose of steroid in order to disrupt their circadian rhythm. The bead mimicked complete disruption, the sort that happens because of “stress, medications and even jet lag,” said Teruel.

Next, the study looked at injections of steroids (coinciding with the typical circadian rhythm), giving the mice steroid so-called spikes 40 times greater than typical levels experienced, but all during the day, times when those spikes might naturally occur.

The findings were interesting: Mice with the bead that released the continuous steroid had more fat cells, but the spiked mice did not -- meaning, mice whose circadian rhythm was disturbed gained weight; mice who had severe daytime “spikes” did not.

Teruel said this study “shows that our fat cells sense whether we are staying on a circadian rhythm.” Disruption of this rhythm, whether from stress hormones or medications, as in the mice with the “bead,” results in increased obesity.

“It’s all about timing,” she said, adding that the results may help doctors figure out ways to better time when they give medications involving steroids so patients can avoid weight gain.

“Can we still give therapies in the right timing windows without causing obesity?” Teruel asked.

It is important to remember that this experiment was completed using mice and additional studies will be needed to further understand circadian pathway disruptions in humans.

Dr. Joseph Cafone is a fourth-year internal medicine and pediatrics resident working in the ABC News Medical Unit.