Understanding Circadian Physiology in Early Childhood: the Role of Napping and Light at Night

178 Pages·2017·1.61 MB·English

University of Colorado, Boulder
CU Scholar
Integrative Physiology Graduate Teses &
Integrative Physiology
Dissertations
Spring 1-1-2016
Understanding Circadian Physiology in Early
Childhood: the Role of Napping and Light at
Night
Lameese Dana Akacem
University of Colorado at Boulder,
UNDERSTANDING CIRCADIAN PHYSIOLOGY IN EARLY CHILDHOOD:
THE ROLE OF NAPPING AND LIGHT AT NIGHT
by
LAMEESE D. AKACEM, M.S.
B.A., University of Colorado Boulder, 2013
M.S., University of Colorado Boulder, 2013

A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirement for the degree of
Doctor of Philosophy
Department of Integrative Physiology
2016
This thesis entitled:
Understanding Circadian Physiology in Early Childhood: The Role of Napping and Light
at Night
written by Lameese D. Akacem
has been approved for the Department of Integrative Physiology

Monique K. LeBourgeois, Ph.D

Kenneth P. Wright Jr., Ph.D.

Monika R. Fleshner, Ph.D.

Robert L. Spencer, Ph.D.

Ann C. Halbower, MD

Date

The final copy of this thesis has been examined by the signatories, and we
find that both the content and the form meet acceptable presentation standards
of scholarly work in the above mentioned discipline.

IRB protocol # FWA00004460 (Brown University); 10-0115 and 15-0080 (University of
Colorado Boulder)

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ABSTRACT
Akacem, Lameese D. (Department of Integrative Physiology)
Understanding Circadian Physiology in Early Childhood: The Role of Napping and Light
at Night

Thesis directed by Assistant Professor Monique K. LeBourgeois

The circadian clock, localized to the suprachiasmatic nucleus of the anterior
hypothalamus, is responsible for regulating rhythms in behavior and physiology
including the timing and secretion of the hormone melatonin. Light is the strongest
environmental input to the circadian system. Specifically, light at night can delay the
timing of the melatonin rhythm and suppress secretion of this sleep -promoting hormone.
Although data on factors that influence the biological clock of adolescents and
adults is expanding, very little is known about circadian physiology in the early
childhood years. The collective aim of this dissertation was to assess the influence of
several modifiable factors on the circadian physiology of young children. In study 1,
sleep and circadian timing were compared between napping and non-napping toddlers.
Napping toddlers had significantly later bedtimes, sleep onset times and circadian
phases than non-napping toddlers. These differences in circadian timing are likely
mediated by the later bedtimes of nappers, which facilitate light exposure later in the
evening thereby delaying the clock. The purpose of study 2 was to quantify the
magnitude of light-induced melatonin suppression in response to evening light exposure
in preschoolers. Children experienced ~90% melatonin suppression in response to a 1
hour long bright light stimulus before bedtime, an effect that persisted up to 50 minutes
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after the light stimulus was terminated. In study 3, we examined children’s evening light
exposure in association with circadian timing. The amount of light children were
exposed to during the 2 hours before bedtime predicted variance in circadian timing
over and above bedtime alone in our sample of young children. The findings of this
dissertation demonstrate the robust sensitivity of the circadian system of young children
to light at night and represent important first steps in understanding fundamental
aspects of circadian physiology during the early years of life.

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DEDICATION

I would like to dedicate this dissertation to my family and friends who have supported
me throughout my graduate career. Specifically, I would like to dedicate this to my
parents who both made many sacrifices to allow me to get the education that I received
and for their continuous encouragement as I pursued my doctorate. I wouldn’t have
been able to get to this far without them.

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ACKNOWLEDGEMENTS

Firstly, I would like to thank my advisor Dr. Monique K. LeBourgeois for mentoring and
supporting me over the past 5 years. I would also like to thank my committee members
Dr. Kenneth P. Wright, Jr., Dr. Monika R. Fleshner, Dr. Robert L. Spencer, and Dr. Ann
C. Halbower. I would like to especially thank Dr. Kenneth P. Wright Jr. for his advice
and support throughout the progress of my dissertation and Dr. Ann C. Halbower for her
help with one of my dissertation studies.

I would like to thank the research participants and their families as well as the staff and
students of the Sleep and Development Laboratory at Brown University and at the
University of Colorado Boulder. I would also like to acknowledge our support: K01-
MH074643 and R01-MH08556 were awarded to Dr. Monique K. LeBourgeois from the
National Institutes of Health, the Summer Graduate School Fellowship, Sleep Research
Society Travel Awards, as well as Travel Awards from the Department of Integrative
Physiology, the Graduate School and the Society for Research on Biological Rhythms
Fellowship Award.

Data from the study presented in Chapter 3 of this dissertation, “Bright Light Exposure
Before Bedtime Suppresses Melatonin in Preschool-Age Children”, was crowd-funded
through the University of Colorado. I would like to acknowledge the following individuals
for their generous contributions to my crowdfunding campaign that made the study
possible: Mia Fill, Corey Theiss, Evan Chinoy, Raymond Najjar, Brian Brady, Jessica
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Calihan, Tsegereda Teklewold, Laura Maguire, Tracy Mott, Matthew Mizer, Kent
Lindquist, Tresdon Jones, Byron Ellis, Dennis Miller, Alex Berger, Kati Pederson,
Leonardo Bermudez, Josiane Broussard, Tim Mickiewicz, Colleen Gribbin, Stephen
Lassonde, Lisa Korte, Roman Mitz, Jayne Bellando, Alexander Jones, Laurie Maguire,
Jim Crossin, Tami Meier, Cristin Bazzanella, Felix Castanar, Karen Schneider, Rebekah
Tribble, Steven Hobbs, Margaret Doucette, Katherine Sharkey, Hannah Craven, Jakob
Sedig, April Schmidt, Becky Crossin, Jennifer Doucette and the company Lumie.

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TABLE OF CONTENTS

Chapter 1. 1
Circadian Phase in Humans: Age-Related Differences and the Influence of Light
Lameese D. Akacem

Introduction 2
Two-Process Model of Sleep Regulation 4
The Circadian System 5
Age-Related Changes in Circadian Phase 14
Light and Circadian Phase 19
Summary 30
References 32

Chapter 2. 55
The Timing of the Circadian Clock and Sleep Differ between Napping and Non-
Napping Toddlers
Lameese D. Akacem, Charles T. Simpkin, Mary A. Carskadon, Kenneth P. Wright Jr.,
Oskar G. Jenni, Peter Achermann, Monique K. LeBourgeois

Abstract 56
Introduction 58
Methods 61
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Results 65
Conclusion 69
Acknowledgements 78
References 79

Chapter 3. 85
Light-Induced Melatonin Suppression in Preschool-Age Children
Lameese D. Akacem, Kenneth P. Wright Jr., Monique K. LeBourgeois

Abstract 86
Introduction 87
Materials and Methods 88
Results 94
Discussion 96
Acknowledgements 101
References 102

Chapter 4. 107
Evening Light Exposure Influences Circadian Timing in Preschool-Age Children:
A Field Study
Lameese D. Akacem, Kenneth P. Wright Jr., Monique K. LeBourgeois

Abstract 108
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