Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Kenneth P. Wright

Second Advisor

Josianne L. Broussard

Third Advisor

Monika R. Fleshner

Fourth Advisor

Robert L. Spencer

Fifth Advisor

Pei-San Tsai

Abstract

Wakefulness at the wrong biological time, referred to as circadian misalignment, as well as not obtaining enough sleep are primary risk factors for negative metabolic health outcomes, including diabetes, weight gain, and obesity. As much as 20% of the workforce in the US works non-traditional hours, some or all of which occur during the night. Additionally, an increasing portion of the population as a whole does not habitually obtain the recommended minimum of 7h of sleep per night.

Food intake is a critical component of energy homeostasis impacting weight gain and obesity. However, this is a complex behavior impacted by physiological and cognitive processes, which change under conditions of circadian misalignment and insufficient sleep. Here, we studied the effect of acute and chronic exposures to circadian misalignment with and without sleep disruption or food intake on physiology and cognition.

First, a simulated shift work protocol was used to examine the impact of acute circadian misalignment and insufficient sleep induced by simulated early morning shift work on metabolic outcomes. We found that food intake after waking under circadian misalignment induced elevated plasma glucose levels without a compensatory insulin response.

Secondly, simulated night shift work and total sleep deprivation protocols were employed to examine how hunger ratings change at night with and without food intake versus typical daytime conditions. We found that hunger ratings followed meal patterns and were lowest at night regardless of food intake. Additionally, we found three factors that explained ~13% of the total variance in hunger rating changes: appetite for specific foods, overall hunger and desire to consume caffeine.

Finally, a protocol of chronic circadian misalignment was used to examine impacts on growth hormone (GH) secretion. During chronic circadian misalignment, GH secretion was decreased during sleep episodes that occurred during the biological daytime, whereas total 24h GH secretion remained unchanged.

Together, these findings demonstrate that metabolic hormones and hunger ratings are altered by acute and chronic circadian misalignment. Further studies are needed to continue to improve the understanding of how circadian misalignment impacts cognitive function and physiological processes contributing to metabolic dysregulation.

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