THE ROLE OF ANIMAL-ASSISTED
INTERVENTIONS IN SUPPORTING
DEPRESSION RECOVERY
A Scoping Systematic Literature Review
FPW van Goolen
I6292533
Faculty of Health, Medicine and Life Sciences (FHML)
Bachelor Health Sciences, Mental Health
GGZ3026 Bachelor Thesis
Maastricht University
Assessor 1: Stefanie Duijvis
Assessor 2: Anouk Hendriks
July third, 2025
,Table of contents
ABSTRACT --------------------------------------------------------------------------------------------------------------------- 2
1. INTRODUCTION ------------------------------------------------------------------------------------------------------ 3
2. METHODS --------------------------------------------------------------------------------------------------------------- 6
2.1 SEARCH STRATEGY ----------------------------------------------------------------------------------------------- 6
2.2 INCLUSION AND EXCLUSION CRITERIA ------------------------------------------------------------------------ 7
2.3 STUDY SELECTION PROCESS ------------------------------------------------------------------------------------ 8
2.4 DATA EXTRACTION ----------------------------------------------------------------------------------------------- 9
2.5 QUALITY AND RISK OF BIAS ASSESSMENT -------------------------------------------------------------------- 10
3. RESULTS ---------------------------------------------------------------------------------------------------------------- 11
3.1 STUDY CHARACTERISTICS AND CONCEPTUALIZATION OF AAIS ----------------------------------------- 11
3.1.1 Terminology and forms of AAIs --------------------------------------------------------------------------- 11
3.1.2 Animal species used in AAIs ------------------------------------------------------------------------------- 13
3.2 PHYSIOLOGICAL EFFECTS OF AAIS -------------------------------------------------------------------------- 14
3.3 REDUCTION OF DEPRESSION SCORES ------------------------------------------------------------------------- 15
3.4 ADDITIONAL PSYCHOLOGICAL OUTCOMES ASSOCIATED WITH DEPRESSION -------------------------- 17
3.4.1 Mood and emotional well-being --------------------------------------------------------------------------- 17
3.4.2 Social participation and loneliness ----------------------------------------------------------------------- 18
3.4.3 Self-reported stress and anxiety --------------------------------------------------------------------------- 19
3.4.4 Hope------------------------------------------------------------------------------------------------------------ 20
3.5 EFFECTS OF AAI STRUCTURE AND ANIMAL SPECIES ON PSYCHOLOGICAL OUTCOMES -------------- 20
3.5.1 Psychological effects of structured versus unstructured AAIs --------------------------------------- 20
3.5.2 Psychological effects of different animal species in AAIs --------------------------------------------- 23
4. DISCUSSION ----------------------------------------------------------------------------------------------------------- 24
4.1 STRENGTHS AND LIMITATIONS -------------------------------------------------------------------------------- 30
4.2 RECOMMENDATIONS FOR FUTURE RESEARCH -------------------------------------------------------------- 31
5. CONCLUSION --------------------------------------------------------------------------------------------------------- 32
APPENDIX A – SEARCH STRINGS ------------------------------------------------------------------------------------- 33
APPENDIX B – BIAS AND QUALITY ASSESSMENTS ------------------------------------------------------------ 34
B.1 SIMPLIFIED ROB 2 ASSESSMENT TABLES -------------------------------------------------------------------------- 34
B.2 SIMPLIFIED AMSTAR ASSESSMENT TABLES ---------------------------------------------------------------------- 41
APPENDIX C – TERMS AND DEFINITIONS OF AAIS ------------------------------------------------------------ 53
APPENDIX D – STUDY CHARACTERISTICS AND RESULTS-------------------------------------------------- 56
REFERENCES ---------------------------------------------------------------------------------------------------------------- 60
1
,Abstract
Background: Human-animal interactions are reported to have positive effects on physiological
and psychological aspects of mental health. Individuals with depressive disorders, which are
highly prevalent and disabling, often experience relapse or limited access to psychological care.
This highlights the need for complementary strategies to treatment as usual to support
depression recovery and improve outcomes.
Methods: This scoping review systematically searched for articles on AAIs and mental well-
being to explore the role AAIs can play in depression recovery and to investigate the
physiological and psychological effects and mechanisms contributing to this process. The
primary and secondary searches were conducted on PubMed, with complementary searches on
PsycNet and ResearchGate. Included articles were published within the last ten years and
focussed on any form of AAI and depression or related mental health outcomes. Seventeen
articles were selected for this review, consisting of both experimental study designs and
systematic reviews and meta-analyses.
Results: The findings revealed extensive variation in terminology, definitions, protocols and
animal species used in AAI research. Despite these variations, AAIs positively affect several
psychophysiological aspects of depression, including regulation of the physiological stress
response, increased neurochemical levels and improved heart rate variability. Additionally,
AAIs reduced feelings of loneliness and anxiety, while enhancing social engagement and
fostering feelings of hope. These results indicate that AAIs could be a valuable addition to
treatment as usual, as physiological and psychological pathways related to depressive disorders
were positively influenced. These findings are particularly relevant considering the current
challenges in mental health care, where AAIs may offer some relief. More extensive research
is needed to clarify the specific mechanisms behind these effects and to better understand the
employability and adaptability of AAIs.
2
, 1. Introduction
More than 280 million people worldwide are affected by one of the most disabling and prevalent
mental disorders: depression (WHO, 2023). It is characterised by the World Health
Organisation (2023) as a mental disorder with a persistent low mood and loss of pleasure and/or
interest in activities that were once enjoyable. Even prosperous countries such as the
Netherlands cannot escape this mental disorder, even though this country makes a conscious
effort to improve their mental health care by conducting research and implementing quality
standards for treatments in national registers (Zorginstituut Nederland, 2019).
Mood disorders such as depression rank among the top ten of highest burden diseases
in the Netherlands due to its debilitating impact on the individual’s quality of life and well-
being (Volksgezondheid en Zorg, n.d.). Depression is also a leading risk factor for suicide,
causing over 700,000 deaths globally each year (WHO, 2023). In the Netherlands, at least five
suicides occur daily (Commissie Actuele Nederlandse Suïcideregistratie, 2025). Although it is
unclear whether all these suicides are due to depression, it remains a major contributor,
emphasizing its severity and threat.
Research also reports a strong relationship between depression and cardiovascular- and
respiratory diseases, cancer, and diabetes (WHO, 2023). Beyond these threatening and possible
fatal effects of depression that highlight its severity, several societal and economic
consequences are reported. Almost ten percent of Dutch adults struggle with depression each
year and general practitioners are aware of 515,600 patients with depressive disorders,
amounting for 1.04 billion euros in healthcare costs for 2019 (Volksgezondheid en Zorg, n.d.).
The WHO (2023) furthermore reports that approximately 12 billion productive workdays are
lost each year due to depression and anxiety, highlighting the negative impact of depression on
economic systems on a global level.
Although depression can affect anyone, it is most frequently reported in adults ranging
from 18 to 34 years old and is more commonly diagnosed in women than in men. Furthermore,
the forms and shapes in which depression can express itself can differ, variance can be found
in duration of episodes, severity and triggers (Bains & Abdijadid, 2023). Whereas all depressive
disorders have a persistent low mood, Persistent Depressive Disorder (Dysthymia) for example
is characterised by its chronic course with symptoms persisting for at least two years, whereas
Premenstrual Dysphoric Disorder has a monthly recurrence where the dysregulation in mood
is only present during the second half of the menstrual cycle (American Psychiatric Association,
3
INTERVENTIONS IN SUPPORTING
DEPRESSION RECOVERY
A Scoping Systematic Literature Review
FPW van Goolen
I6292533
Faculty of Health, Medicine and Life Sciences (FHML)
Bachelor Health Sciences, Mental Health
GGZ3026 Bachelor Thesis
Maastricht University
Assessor 1: Stefanie Duijvis
Assessor 2: Anouk Hendriks
July third, 2025
,Table of contents
ABSTRACT --------------------------------------------------------------------------------------------------------------------- 2
1. INTRODUCTION ------------------------------------------------------------------------------------------------------ 3
2. METHODS --------------------------------------------------------------------------------------------------------------- 6
2.1 SEARCH STRATEGY ----------------------------------------------------------------------------------------------- 6
2.2 INCLUSION AND EXCLUSION CRITERIA ------------------------------------------------------------------------ 7
2.3 STUDY SELECTION PROCESS ------------------------------------------------------------------------------------ 8
2.4 DATA EXTRACTION ----------------------------------------------------------------------------------------------- 9
2.5 QUALITY AND RISK OF BIAS ASSESSMENT -------------------------------------------------------------------- 10
3. RESULTS ---------------------------------------------------------------------------------------------------------------- 11
3.1 STUDY CHARACTERISTICS AND CONCEPTUALIZATION OF AAIS ----------------------------------------- 11
3.1.1 Terminology and forms of AAIs --------------------------------------------------------------------------- 11
3.1.2 Animal species used in AAIs ------------------------------------------------------------------------------- 13
3.2 PHYSIOLOGICAL EFFECTS OF AAIS -------------------------------------------------------------------------- 14
3.3 REDUCTION OF DEPRESSION SCORES ------------------------------------------------------------------------- 15
3.4 ADDITIONAL PSYCHOLOGICAL OUTCOMES ASSOCIATED WITH DEPRESSION -------------------------- 17
3.4.1 Mood and emotional well-being --------------------------------------------------------------------------- 17
3.4.2 Social participation and loneliness ----------------------------------------------------------------------- 18
3.4.3 Self-reported stress and anxiety --------------------------------------------------------------------------- 19
3.4.4 Hope------------------------------------------------------------------------------------------------------------ 20
3.5 EFFECTS OF AAI STRUCTURE AND ANIMAL SPECIES ON PSYCHOLOGICAL OUTCOMES -------------- 20
3.5.1 Psychological effects of structured versus unstructured AAIs --------------------------------------- 20
3.5.2 Psychological effects of different animal species in AAIs --------------------------------------------- 23
4. DISCUSSION ----------------------------------------------------------------------------------------------------------- 24
4.1 STRENGTHS AND LIMITATIONS -------------------------------------------------------------------------------- 30
4.2 RECOMMENDATIONS FOR FUTURE RESEARCH -------------------------------------------------------------- 31
5. CONCLUSION --------------------------------------------------------------------------------------------------------- 32
APPENDIX A – SEARCH STRINGS ------------------------------------------------------------------------------------- 33
APPENDIX B – BIAS AND QUALITY ASSESSMENTS ------------------------------------------------------------ 34
B.1 SIMPLIFIED ROB 2 ASSESSMENT TABLES -------------------------------------------------------------------------- 34
B.2 SIMPLIFIED AMSTAR ASSESSMENT TABLES ---------------------------------------------------------------------- 41
APPENDIX C – TERMS AND DEFINITIONS OF AAIS ------------------------------------------------------------ 53
APPENDIX D – STUDY CHARACTERISTICS AND RESULTS-------------------------------------------------- 56
REFERENCES ---------------------------------------------------------------------------------------------------------------- 60
1
,Abstract
Background: Human-animal interactions are reported to have positive effects on physiological
and psychological aspects of mental health. Individuals with depressive disorders, which are
highly prevalent and disabling, often experience relapse or limited access to psychological care.
This highlights the need for complementary strategies to treatment as usual to support
depression recovery and improve outcomes.
Methods: This scoping review systematically searched for articles on AAIs and mental well-
being to explore the role AAIs can play in depression recovery and to investigate the
physiological and psychological effects and mechanisms contributing to this process. The
primary and secondary searches were conducted on PubMed, with complementary searches on
PsycNet and ResearchGate. Included articles were published within the last ten years and
focussed on any form of AAI and depression or related mental health outcomes. Seventeen
articles were selected for this review, consisting of both experimental study designs and
systematic reviews and meta-analyses.
Results: The findings revealed extensive variation in terminology, definitions, protocols and
animal species used in AAI research. Despite these variations, AAIs positively affect several
psychophysiological aspects of depression, including regulation of the physiological stress
response, increased neurochemical levels and improved heart rate variability. Additionally,
AAIs reduced feelings of loneliness and anxiety, while enhancing social engagement and
fostering feelings of hope. These results indicate that AAIs could be a valuable addition to
treatment as usual, as physiological and psychological pathways related to depressive disorders
were positively influenced. These findings are particularly relevant considering the current
challenges in mental health care, where AAIs may offer some relief. More extensive research
is needed to clarify the specific mechanisms behind these effects and to better understand the
employability and adaptability of AAIs.
2
, 1. Introduction
More than 280 million people worldwide are affected by one of the most disabling and prevalent
mental disorders: depression (WHO, 2023). It is characterised by the World Health
Organisation (2023) as a mental disorder with a persistent low mood and loss of pleasure and/or
interest in activities that were once enjoyable. Even prosperous countries such as the
Netherlands cannot escape this mental disorder, even though this country makes a conscious
effort to improve their mental health care by conducting research and implementing quality
standards for treatments in national registers (Zorginstituut Nederland, 2019).
Mood disorders such as depression rank among the top ten of highest burden diseases
in the Netherlands due to its debilitating impact on the individual’s quality of life and well-
being (Volksgezondheid en Zorg, n.d.). Depression is also a leading risk factor for suicide,
causing over 700,000 deaths globally each year (WHO, 2023). In the Netherlands, at least five
suicides occur daily (Commissie Actuele Nederlandse Suïcideregistratie, 2025). Although it is
unclear whether all these suicides are due to depression, it remains a major contributor,
emphasizing its severity and threat.
Research also reports a strong relationship between depression and cardiovascular- and
respiratory diseases, cancer, and diabetes (WHO, 2023). Beyond these threatening and possible
fatal effects of depression that highlight its severity, several societal and economic
consequences are reported. Almost ten percent of Dutch adults struggle with depression each
year and general practitioners are aware of 515,600 patients with depressive disorders,
amounting for 1.04 billion euros in healthcare costs for 2019 (Volksgezondheid en Zorg, n.d.).
The WHO (2023) furthermore reports that approximately 12 billion productive workdays are
lost each year due to depression and anxiety, highlighting the negative impact of depression on
economic systems on a global level.
Although depression can affect anyone, it is most frequently reported in adults ranging
from 18 to 34 years old and is more commonly diagnosed in women than in men. Furthermore,
the forms and shapes in which depression can express itself can differ, variance can be found
in duration of episodes, severity and triggers (Bains & Abdijadid, 2023). Whereas all depressive
disorders have a persistent low mood, Persistent Depressive Disorder (Dysthymia) for example
is characterised by its chronic course with symptoms persisting for at least two years, whereas
Premenstrual Dysphoric Disorder has a monthly recurrence where the dysregulation in mood
is only present during the second half of the menstrual cycle (American Psychiatric Association,
3
