How Circadian Disruption Can Cause Obesity

Regular readers of these pages should be well aware of the mounting evidence that points to lack of sleep as an important driver of the obesity epidemic. Not only does lack of sleep increase cravings for “junk” foods, reduce energy levels and physical activity, but it also negatively affects metabolism.

In addition, it now seems that simply disrupting the natural (24-h) circadian rhythm and sleep-wake cycle (as seen in shift workers, young parents, and people who frequently travel across time zones) may also promote weight gain.

This phenomenon was now carefully examined by Ilia Karatsoreos and colleagues from Rockefeller University, NY, in a paper just published in the Proceedings of the National Academy of Science (USA).

As the authors point out:

“Over the past 100 y, especially with the advent of electric lighting, modern society has resulted in a round-the-clock lifestyle, in which natural connections between rest/activity cycles and environmental light/dark cycles have been degraded or even broken.”

To examine the effects of this disruption of circadian rhythm in mammals, the researchers exposed healthy mice to 20-h light/dark cycles, incongruous with their endogenous ∼24-h circadian period.

Over time, this disruption of circadian rhythm resulted in accelerated weight gain and obesity, as well as changes in metabolic hormones.

In addition, the researchers found marked in changes in the brains of these animals including loss of dendritic length and decreased complexity of neurons in brain regions important for complex executive functions and emotional control.

Consistent with these changes in brain architecture, disrupted animals showed decreased cognitive flexibility and changes in emotionality in experiments designed to test these functions.

These findings certainly support the notion that chronically disrupting the natural (24-h) circadian rhythm in mammals can lead to substantial changes in behaviour and alterations in metabolism that would promote weight gain.

Certainly further reason to make a careful evaluation of sleep history an essential part of any clinical assessment for weight gain and obesity.

Edmonton, Alberta

Karatsoreos IN, Bhagat S, Bloss EB, Morrison JH, & McEwen BS (2011). Disruption of circadian clocks has ramifications for metabolism, brain, and behavior. Proceedings of the National Academy of Sciences of the United States of America PMID: 21220317