Emotional expressivity in early adulthood as a predictor of dementia and Alzheimer's disease in ...

195 Pages·2015·1.38 MB·English

Emotional expressivity in early adulthood
as a predictor of dementia and Alzheimer’s
disease in late adulthood

by

Jill M. Morrison

A thesis
presented to the University of Waterloo
in fulfillment of the
thesis requirement for the degree of
Master of Science
in
Health Studies and Gerontology

Waterloo, Ontario, Canada, 2015

©Jill M. Morrison 2015
Author’s Declaration
I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any
required final revisions, as accepted by my examiners.
I understand that my thesis may be made electronically available to the public.

ii
Abstract
Background: As the global population ages, the prevalence of age-related disorders, such as
dementia, is increasing. Dementia is a condition of progressive deterioration of cognitive ability that
leads to functional deficits. The primary subtype of dementia is Alzheimer’s disease (AD). Currently,
there is no cure for AD or other major forms of dementia (e.g., vascular dementia) so prevention is
the best approach for reducing the burden of these conditions. Emotions experienced across the
lifespan may affect the development of dementia and AD, given their high involvement in cognitive,
cardiovascular and psychosocial processes. Emotions may be neuroprotective by promoting the
development of cognitive resources that allow resistance to pathologic changes in the brain.
Alternatively, emotions may be neuropathogenic by contributing to vascular risk factors and evoking
the stress response. The objective of this study is to investigate a potential novel association of
emotional expressivity in early adulthood with dementia and AD in late life.
Methods: Data from the Nun Study, a longitudinal study of 678 religious sisters who were aged 75+
at baseline in 1991, were used for the investigation. Data include annual cognitive and physical
assessments, post-mortem brain autopsies and historical documents obtained from convent archives.
Archival autobiographies handwritten in early adulthood (mean age=22) were available for 180 U.S.-
born participants. Autobiographies were scored for emotional expressivity, as well as for idea density,
a measure of written language skills known to be associated with dementia and AD. Emotional
expressivity was classified as high (i.e., top two quartiles) or low (i.e., bottom two quartiles) based on
within-convent ranking of number of emotion words. Dementia was diagnosed if individuals
displayed an inability to perform activities of daily living, and cognitive impairment on a battery of
neuropsychological tests, according to standard criteria. A diagnosis of AD required evidence of
dementia and AD neuropathology. Samples were selected for the analysis of dementia (n=149) and
AD (n=85) based on the availability of data on dementia, AD neuropathology and all covariates of
interest, and on restriction by low education.
Positive, negative, and overall emotional expressivity (i.e., the sum of positive and negative
emotion words) were investigated in association with both dementia and AD using multivariate
logistic regression analysis. Additional analyses were performed to investigate the association of
emotional expressivity with dementia. These included dividing the negative emotional expressivity
variable into three (as opposed to two) categories, and testing the interaction between positive and
iii
negative expressivity in association with dementia. All final models were stratified by idea density
and adjusted for age and apolipoprotein E-ε4 (APOE-ε4).
Results: The association of emotional expressivity with dementia and AD was modified by idea
density. Among individuals with high idea density, those with high emotional expressivity, regardless
of valence (i.e., overall, positive and negative), were consistently at an increased risk of dementia and
AD compared to those with low emotional expressivity. In particular, overall emotional expressivity
was significantly associated with dementia in this subgroup (odds ratio [OR]=2.60, 95% confidence
interval [CI]=1.04-7.11). Among individuals with low idea density, those with high overall and
negative emotional expressivity were at a decreased risk of dementia and AD compared to individuals
with low emotional expressivity. Positive emotional expressivity was associated with an increased
risk of dementia and AD. None of the associations of emotional expressivity with dementia or AD
were significant in the low idea density subgroup.
The associations did not reach statistical significance among individuals with low idea
density in the additional analysis of emotional expressivity with dementia. However, among
individuals with high idea density, moderate, but not high, negative emotional expressivity was
associated with an increased risk of dementia (OR=3.59, 95% CI=1.13-11.89). Furthermore, high
negative emotional expressivity was associated with an increased risk of dementia among individuals
with low positive emotional expressivity (OR=8.17, 95% CI=1.66-58.96).
Discussion: The results support emotional expressivity in early adulthood as a potential predictor of
dementia and AD in late adulthood. Idea density, a known risk factor of dementia and AD, modifies
the association. High emotional expressivity, regardless of valence, is associated with an increased
risk of dementia and AD when cognitive risk is otherwise low (i.e., high idea density), whereas
overall and negative expressivity are associated with a decreased risk of dementia and AD when
cognitive risk is high (i.e., low idea density). Furthermore, as predicted, the effect of negative
emotional expressivity was modified by positive emotional expressivity: negative expressivity was
only associated with an increased risk of dementia when positive expressivity was low, suggesting
that positive emotions may counteract the adverse effects of negative emotions. Taken all together,
the results provide evidence for a potential association of emotional expressivity in early adulthood
with dementia and AD in late life. These findings suggest the importance of emotional expressivity as
a predictor of long-term health outcomes, including dementia and AD. As such, emotions may serve
as a potential target for future dementia and AD prevention strategies.
iv
Acknowledgments
First and foremost, I would like to express my gratitude to Dr. Suzanne Tyas, who has supervised and
mentored me during my time at UW. Her guidance, dedication, support and patience over the course
of my studies have helped me to grow both personally and professionally, and I thank her greatly.
I would also like to acknowledge my committee members, Dr. John Mielke and Dr. Myra Fernandes,
for their contributions to this project.
I would like to thank the faculty and staff of SPHHS, especially those with whom I have worked, for
the many teaching moments and words of encouragement, which have contributed to my professional
development.
Thank you to my classmates, teammates, officemates and roommates who have made UW feel like
home. A special thanks to Rachel, Mushaal and Darly for keeping my head on straight!
Thank you to the SSND community for their inspired participation in the Nun Study, and in particular
to S. Rebecca and S. Betty for their prayers for the successful completion of my thesis.
I would like to acknowledge my family and friends who have offered support, prayers and times of
relaxation and refreshment to keep me going over the course of my degree. I would especially like to
thank my parents for their unconditional love and support.
I thank God for all of you who have made my time working on this thesis a rewarding experience!

v
Table of Contents
Author's Declaration .......................................................................................................... ii 
Abstract ............................................................................................................................ iii 
Acknowledgments ............................................................................................................. v 
Table of Contents .............................................................................................................. vi 
List of Figures .....................................................................................................................xi 
List of Tables ..................................................................................................................... xii 
List of Abbreviations ........................................................................................................ xiii 
Chapter 1 Introduction ...................................................................................................... 1 
Chapter 2 Literature Review .............................................................................................. 3 
2.1 The Aging Population and Age‐Related Diseases ................................................................... 3 
2.2 Dementia ............................................................................................................................. 5 
 Overview ................................................................................................................................ 5 
 Etiology of Dementia ............................................................................................................. 6 
 Diagnosis of Dementia ........................................................................................................... 7 
2.3 Alzheimer’s Disease (AD) ...................................................................................................... 7 
 Overview ................................................................................................................................ 7 
 Etiology of Alzheimer’s Disease ............................................................................................. 9 
 Diagnosis of Alzheimer’s Disease ........................................................................................ 11 
2.4 Vascular Dementia (VaD) .................................................................................................... 13 
 Overview .............................................................................................................................. 13 
 Etiology of Vascular Dementia ............................................................................................ 14 
 Diagnosis of Vascular Dementia .......................................................................................... 15 
2.5 Dementia, AD and VaD ....................................................................................................... 16 
 Mixed Dementia .................................................................................................................. 16 
 Common Risk and Protective Factors.........…......................................................................17 
vi
2.5.2.1 Demographic Factors.........….......................................................................................17 
  2.5.2.2 Genetic Factors.........…................................................................................................18 
  2.5.2.3 Cognitive Factors.........….............................................................................................18 

  2.5.2.4 Psychosocial Factors.........…........................................................................................20 

  2.5.2.5 Factors Related to Physical Health.........…..................................................................21 

  2.5.2.6 Other Factors.........…...................................................................................................23 

2.5.2.7 Risk Across the Lifespan.........…...................................................................................24 
2.6 Emotions ............................................................................................................................ 24 
 Cognitive Effects of Emotions .............................................................................................. 25 
2.6.1.1 The Limbic System.........…...........................................................................................25 

  2.6.1.2 Perception and Attention.........…................................................................................26 

  2.6.1.3 Learning and Memory.........…......................................................................................27 
2.6.1.4 Decision‐Making and Problem‐Solving...........…..........................................................27 

2.6.1.5 The Broaden‐and‐Build Theory........................….........................................................28 

 Psychosocial Effects of Emotions ........................................................................................ 28 
2.6.2.1 The Reticular Formation.........…..................................................................................28 

  2.6.2.2 Emotions and Psychosocial Experience.........…...........................................................29 

 Physical Effects of Emotions ................................................................................................ 30 
2.6.3.1 The Autonomic Nervous System.........…......................................................................30 

  2.6.3.2 Cardiovascular Effects of Emotions.........….................................................................30 

 Emotions, Stress and Emotion Regulation .......................................................................... 31 
2.6.4.1 Stress as a Risk Factor for Dementia, AD and VaD.........…...........................................31 
  2.6.4.2 Coping and Emotion Regulation.......................................…........................................32 

  2.6.4.3 Suppression and Expression of Emotions.........…........................................................33 

 Factors Affecting Emotional Expressivity ............................................................................ 34 
2.7 Summary ............................................................................................................................ 34 
Chapter 3 Study Rationale ............................................................................................... 36 
3.1 Motivation ......................................................................................................................... 36 
 Gaps in Current Literature ................................................................................................... 36 
 Plausible Mechanisms ......................................................................................................... 37 
vii
3.2 Objective ............................................................................................................................ 38 
Chapter 4 Methods .......................................................................................................... 40 
4.1 Literature Search ................................................................................................................ 40 
4.2 Data Source: The Nun Study ............................................................................................... 41 
 Background .......................................................................................................................... 41 
 Population ........................................................................................................................... 41 
 Data Collection .................................................................................................................... 41 
4.3 Study Design ...................................................................................................................... 42 
 Analytic Sample ................................................................................................................... 42 
 Exposure Measures ............................................................................................................. 43 
 Outcome Measures ............................................................................................................. 46 
 Covariates ............................................................................................................................ 47 
4.4 Analytic Strategy ................................................................................................................ 49 
 Descriptive Analysis ............................................................................................................. 49 
 Multivariate Analysis ........................................................................................................... 49 
4.5 Ethics Approval .................................................................................................................. 51 
Chapter 5 Results ............................................................................................................. 52 
5.1 Descriptive Statistics .......................................................................................................... 52 
 Sample Selected for the Dementia Analyses ....................................................................... 52 
 Sample Selected for the AD Analyses .................................................................................. 59 
 Sample Selected for the VaD Analyses ................................................................................ 65 
5.2 Multivariate Logistic Regression Models ............................................................................. 65 
 Lower Idea Density Subgroup .............................................................................................. 66 
 Higher Idea Density Subgroup ............................................................................................. 67 
 Further Investigation Using the Sample for Dementia Analyses ......................................... 68 
5.2.3.1 Emotional Expressivity Categorized by Tertiles.........…...............................................68 

    5.2.3.1.1 Low Idea Density........…...............................................................................68 
    5.2.3.1.2 Higher Idea Density........…...........................................................................69 

viii
5.2.3.2 The Association Between Negative Emotional Expressivity and Dementia,  
Modified by Positive Expressivity........….................................................................................70 

 Model Diagnostics ............................................................................................................... 72 
5.3 Sensitivity Analysis ............................................................................................................. 72 
 Dementia Analyses Using the Subset Selected for the Analyses of AD ............................... 72 
 Analysis of Models Not Stratified by Idea Density .............................................................. 73 
Chapter 6 Discussion ........................................................................................................ 75 
6.1 Summary of Findings .......................................................................................................... 75 
 Emotional Expressivity, Dementia, and the Theory of Cognitive Reserve .......................... 76 
 Overall Emotional Expressivity and the Risk of Dementia ................................................... 76 
 Negative Expressivity and the Modifying Effects of Positive Expressivity ........................... 79 
 The Modifying Effect of Idea Density .................................................................................. 80 
6.2 Strengths and Limitations ................................................................................................... 81 
 Limitations ........................................................................................................................... 81 
 Strengths .............................................................................................................................. 82 
6.3 Implications........................................................................................................................ 84 
6.4 Future Directions ................................................................................................................ 84 
 Replicate the Study .............................................................................................................. 85 
 Validate the Emotional Expressivity Measure ..................................................................... 85 
 Clarify Mechanisms Underlying the Association Between Emotional Expressivity and 
Dementia ...................................................................................................................................... 86 
 Expand the Analysis of AD and VaD..................................................................................... 86 
6.5 Conclusion .......................................................................................................................... 87 
References ....................................................................................................................... 88 
Appendix A. Literature Search Construct and Article Summaries ................................... 114 
Appendix B. Cerebral Infarct Sensitivity Analysis ........................................................... 116 
Appendix C. Assessment of Non‐Response .................................................................... 129 
ix
Appendix D. Analysis of the Association Between Emotional Expressivity and Dementia 
Without Restriction by Education .................................................................................. 136 
Appendix E. All Multivariate Logistic Regression Models ............................................... 141 
Appendix F. Full Analysis of Alzheimer’s Disease Using Alternative Samples ................. 164 
Appendix G. Sensitivity Analysis of the Association of Emotional Expressivity with 
Dementia using the Subset for the Analysis of AD ......................................................... 178 

x