JVME-35.4.-005 487..495


Purdue Conference on the Human–Animal Bond

The Benefits of Human–Companion Animal
Interaction: A Review

Sandra B. Barker g Aaron R. Wolen

ABSTRACT

This article provides a review of research published since 1980 on the benefits of human–companion animal interaction.

Studies focusing on the benefits of pet ownership are presented first, followed by research on the benefits of interacting with

companion animals that are not owned by the subject (animal-assisted activities). While most of the published studies are

descriptive and have been conducted with convenience samples, a promising number of controlled studies support the health

benefits of interacting with companion animals. Future research employing more rigorous designs and systematically building

upon a clearly defined line of inquiry is needed to advance our knowledge of the benefits of human–companion animal

interaction.

Key words: research review, human–companion animal interaction, animal-assisted activities, controlled trials, animal-assisted
intervention, human–animal bonding

INTRODUCTION
Many articles have been published on the benefits of
human–companion animal interaction and this review,
while comprehensive, is by no means exhaustive. The
review is the result of a comprehensive search of published
research since 1980 (through June 2007) using the Medline,
PsycINFO, and CINAHL bibliographic databases. The
following key words were used to retrieve articles assessing
the benefits of human–animal interaction: animal bond;
animal companions; animal-assisted therapy; canine visitation;
companion animal; companion cat; dogs and health; human–
animal; human–pet; pets and health; pet companionship;
pet owners; pet ownership; pet therapy. Dissertations and
book chapters were omitted, as were articles published
in journals that were not verified to be peer-reviewed
in Ulrich’s Periodicals Directory. Articles published in a
language other than English and those focusing on service/
assistance animals, police dogs, horses, non-companion
animals (e.g., dolphins), or the death of a pet were also
omitted.

Abstracts were then reviewed to select articles that involved
some type of empirical design, thereby excluding literature
reviews and anecdotal reports. The articles were reviewed
and sorted into content categories by primary outcome
and/or target subject (e.g., nursing-home residents, chil-
dren, psychiatric patients). The authors then selected
the categories that represented the most frequently
investigated areas. These categories serve as the framework
for this review. Studies focusing on pet ownership are
presented first, followed by those focusing on animal-
assisted activities (AAA), defined as interventions involving
interactions with animals that are not owned by the subjects
in the study.

PET OWNERSHIP
Most studies of pet ownership are descriptive, with data
collected primarily from interviews and surveys of

convenience samples, thus making them difficult to com-
pare beyond noting whether the results appear to support a
commonly assessed outcome. This section will separately
review studies of the physiological and psychosocial
benefits of pet ownership.

Physiological Benefits of Pet Ownership
A landmark study by Friedmann et al of decreased
mortality in pet owners one year after discharge from a
coronary care unit1 inspired further research into the
potential cardiovascular (CV) and general health benefits
of pet ownership. The results were mixed. A longitudinal
study on 369 patients participating in the Cardiac
Arrhythmia Suppression Trial (CAST) confirmed the results
of the original Friedmann trial, finding that pet ownership
and social support predicted survival one year after a
myocardial infarction.2 Extending these studies, Friedmann
et al analyzed heart rate (HR) variability in a sample
of CAST participants with healed myocardial infarcts,
with the results suggesting that altered cardiac autonomic
modulation may be a possible mechanism of action
of reduced mortality in pet owners compared with non-
owners.3

Several large Australian studies have also researched pet
ownership and CV health. One study used health screenings
of 5,741 volunteers to compare the CV health of those who
owned a pet versus those who did not. Pet owners were
found to have lower levels of CV risk factors than those
without pets.4 However, a follow-up survey of over 2,500
community-based adults failed to show any CV benefit from
pet ownership.5 These surveys differed substantially in their
methodologies, which may explain the conflicting results:
the former study involved self-selected participants and
underrepresented pet owners compared to the Australian
population,5 while the latter survey involved a representa-
tive sample randomly selected for inclusion in a long-
itudinal health study.

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Another large (n¼1,011) Australian survey concluded that
dog and cat owners were in better health than non-owners,
based on either physician visits or medication use (but not
both), translating into savings of $988 million AU$ in health
care costs.6 Those with a close bond to their pets had
the additional benefits of less loneliness and a greater
social support network. The German Socio-Economic Panel
Survey of a nationally representative sample of approxi-
mately 10,000 participants supports these findings.7 Two
surveys, conducted five years apart, showed the least
physician visits among those who continuously owned a
pet during the five year period, followed by those who
acquired a pet during the period. Looking at adherence to
treatment as a health outcome, researchers have reported
that pet ownership predicts adherence to CV rehabilitation,
while numerous personality and psychosocial variables do
not.8 Pet owners in this sample of 81 patients were far more
likely to complete cardiac rehabilitation than those who did
not own a pet.

Interviews with elderly Medicare enrollees in a large,
longitudinal study found that pet owners reported fewer
visits to physicians over a one-year period and dogs
appeared to serve as a buffer from the impact of stressful
life events.9 In another elderly sample, pet attitudes and pet
ownership were significant but weak predictors of main-
taining improved levels of health and morale in a long-
itudinal four-year study.10 In contrast, other descriptive
studies have reported no significant difference between pet
owners and those without pets in the use of health
services;11,12 morale, locus of control, social interaction,
mental status, psychological symptoms, and physical
abilities;13 use of daily medication or presence of medical
problems;14 or multiple health variables, mortality, or
healthy behaviors.15 One large-scale survey of Australian
seniors reported an association between caring for a pet and
negative health outcomes.16 Pachana et al attempted to
identify factors contributing to such inconsistent results by
analyzing a large, longitudinal health data set of 6,404 older
Australian women, and found that age, mental and physical
health, living arrangements, and housing were all strongly
related to pet ownership.17 Confounding of outcomes by
such demographic variables may have contributed to the
inconsistencies in reported results. In addition, studies that
rely on self-report of pet owners yield subjective results.

Headey has provided another possible explanation for these
conflicting findings by differentiating between the social
science and medical research methodologies used.18 He
asserts that the survey-based methods used in social science
research provide evidence of health benefits associated with
pet ownership, whereas controlled clinical trials in medical
research seek causal links between pet ownership and
specific medical conditions.

A number of experimental studies have focused on the
effect of human–pet interaction on CV indicators, with
mixed results. In a randomized, repeated-measures cross-
over design, Moody et al found no significant differences
in systolic (SBP), diastolic blood pressure (DBP), or HR
between hypertensive pet owners (with and without their
pets present during testing) and those who did not own
pets.19 Similarly, a study examining the effects of petting
one’s own dog versus an unfamiliar dog found that HR and
BP were unaffected by the participant’s relationship with

the animal, and HR only decreased during the control
condition of quietly reading a book.20 In contrast, several
studies that have included a cognitive stressor consistently
found that pets reduce indicators of CV stress. Early work
on the subject by Allen et al demonstrated this effect by
randomly assigning female dog lovers to complete a mental
task accompanied by either their pet dog, which produced
little stress reactivity in skin conductance, BP, and HR, or by
a close friend, which increased overall stress reactivity.21

In a more recent randomized controlled trial, Allen et al
randomly assigned hypertensive adults starting lisinopril
(an angiotensin-converting enzyme [ACE] inhibitor) to a
group acquiring a dog or cat or to a wait-list control group
for six months.22 The physiological response to stress
(SBP, HR, and plasma renin activity) at home was found
to be lower in those assigned to pet ownership compared
with the control group without pet ownership. In addition,
pet owners performed higher in mental tasks. Lisinopril
reduced only resting BP. Other studies that have included a
mental stress task have also reported positive findings.
A related study comparing married couples with and
without pets found that pet owners had decreased resting
BP and HR, and a lower reactivity in SBP and HR during
a mental stress task, with faster return to baseline.23 A
smaller study reported reduced BP, but not HR, when
petting a dog while reading aloud.24 These experimental
studies collectively support a beneficial effect of pet own-
ership on CV stress reactivity that warrants further
investigation.

The possibility of an association between pet ownership and
CV health has prompted other researchers to investigate
whether owning a pet increases physical activity. One
observational study found that dog owners walked more
frequently, but not for longer, than non-owners,25 while a
survey-based study found the opposite: dog owners walked
for longer, but not more frequently, than non-owners, and
dog owners were less likely to meet recommended levels of
physical activity.26 A comparison of 3,075 Medicare recipi-
ents in the Health ABC Study found no difference in the
frequency of walking for exercise or of any physical activity
in those with and without pets; although older dog owners
engaged in more physical activity overall.27 In contrast, a
large-scale, one-year longitudinal study of 995 community-
based seniors in Canada found pet owners to be younger
and more physically active than those without pets.28 In this
age- and sex-stratified random sample, pet ownership
significantly modified the relationship between social
support and change in psychological well-being over the
study period. While age may account for the increased
physical activity, those without pets were noted to engage in
comparatively fewer activities of daily living.

Conflicting findings on physical activity may be explained
by confounding variables that have not been controlled for
in these studies. For example, one survey found that
dog size mediated the frequency of physical activity, with
owners of medium- and large-sized dogs walking more
often.29 A sense of responsibility for the health and well-
being of one’s dog was also found to mediate the relation-
ship between physical activity and dog ownership.30

These studies emphasize the importance of investigating
mediating variables that may play a role in the physiological
benefits of pet ownership.

488 JVME 35(4) � 2008 AAVMC



Psychosocial Benefits of Pet Ownership
Several descriptive studies have documented the closeness
between people and their pets, including dog owners who
were found to be as emotionally close to their dogs as to
their closest family member,31 pet owners with HIV or
AIDS who likened their relationship with their pets to that
with their family members,32 and owners whose cats
provided a source of emotional support.33 Similarly, a
retrospective study reported that survivors of sexual
abuse rated their pets as more supportive during childhood
than humans.34

A number of surveys have assessed the association between
pet ownership and depression. A large Internet survey
found that unmarried female pet owners reported
the fewest depressive symptoms, while unmarried
male pet owners report the most.35 An equally large
survey (n¼2,551) of Australian seniors reported higher
levels of depression in pet owners,16 while a smaller group
of elderly patients sampled in a physician’s office revealed
no significant differences in depression, happiness, life
satisfaction, hobbies, and interests between those with and
without pets.14 Furthermore, no association was found
between pet ownership and depression in a large survey
of gay and bisexual men (n¼1,872) participating in the
Multicenter AIDS Cohort Study.36

Several descriptive studies have examined the relationship
between pet ownership and mood in people living alone. In
women living alone, pets have been associated with
increased morale37 and decreased loneliness.38 A more
recent study found that cats alleviated negative moods
equally as well as a human partner, but that only a human
partner strengthened positive moods.39 Similarly, an obser-
vational study has concluded that cats seem to help
compensate for the depressive moods of single adults.40

These descriptive studies suggest that pet ownership may
be associated with some benefits to mood in select samples.

The psychological effect of pets on children has received
some attention in the literature, with mostly positive
outcomes reported. Descriptive studies have reported that
pets increase autonomy, self-concept, and self-esteem in
some elementary school children.41 Positive relationships
have also been found between parents’ perceived compe-
tence of their children and pet attachment in kindergarten
children, self-reported empathy and pet attachment in
kindergarten boys, and attachment and parents’ perceived
empathy in fifth-grade children.42 Other survey research
with school-age children has reported that children who
prefer both dogs and cats have higher levels of empathy
than those who prefer one or the other, and children who are
highly attached to their pets are more empathic than those
who are less attached.43 Croatian researchers have also
found a positive relationship between pet attachment and
empathy, increased social orientation, and a positive family
climate in school-age children.44

These descriptive studies of convenience samples call
attention to the need for more rigorous experimental
studies of the psychosocial effects of pet ownership on
children and adults. The validity of most of the current
studies is threatened by the reliance on convenience
samples and the presence of uncontrolled extraneous
variables.

ANIMAL-ASSISTED ACTIVITIES/THERAPY
The authors recognize the differences between animal-
assisted therapy (AAT)—the purposeful incorporation of
therapy animals into an individual’s treatment plan—and
the more general AAA, such as pet visitation. However,
published studies do not consistently differentiate between
AAT and AAA. Therefore, to minimize confusion and for
ease of reading, the more general term AAA will be used to
encompass all activities involving a companion animal that
is not owned by the recipient of services. This section
presents research focusing on CV outcomes, followed
by outcomes in clinical samples, with a final section on
AAA and children.

Cardiovascular Benefits
A number of studies have investigated the effect of AAA on
CV response and, like the pet ownership studies already
presented, report mixed results. One reason may be that the
studies vary greatly in terms of samples, AAA interven-
tions, and study conditions. While several studies have
incorporated mental stressors into their experimental
designs, the large variety of mental stressors employed
may also contribute to the inconsistent results. A few
studies have reported no difference in BP and HR associated
with dog presence,45,46 while most have reported reductions
in BP associated with dog presence,47,48 tactile interaction
with a dog,49 and, in one study, the presence of a pet goat as
well.50 Studies comparing AAA with quiet reading have
found greater BP reductions in the quiet reading condi-
tion.48,51 However, petting one’s own dog, as opposed
to petting an unfamiliar dog, produced similar declines in
BP.52 Using HR variability as a surrogate index of autonomic
activity, Japanese researchers have used a repeated-
measures crossover design to assess seniors walking in a
park either alone or with a research dog. Their results
demonstrated that the dog’s presence in the park, as well as
at home, increased parasympathetic neural activity, which is
generally associated with stress reduction.53

Similar to the results of studies on pet ownership studies on
CV stress reactivity, the inclusion of a mental stressor in
studies of AAA appears to contribute to positive findings,
lending further support to the potential benefits of interact-
ing with companion animals on stress reactivity and the
importance of conducting research grounded in theoretical
models, namely stress models.

Benefits for Individuals with Psychiatric Disorders
Several experimental studies have reported positive effects
of AAA with therapy dogs on hospitalized psychiatric
patients, including reductions in fear and anxiety,54,55

increased attendance at occupational therapy,56 and more
pro-social behaviors.57 Comparing recently discharged
psychiatric patients in two matched adult homes, research-
ers found improvements in social interaction, psychosocial
function, life satisfaction, mental function, depression, social
competence, and psychological well-being in those
residing in the home receiving six weekly puppy visits.58

While no differences were detected in functioning and
treatment response in geriatric psychiatry patients who
were randomly assigned to AAA with therapy dogs or to an
exercise group, decreased irritability was noted in women
with dementia in both groups.59 In one study of depressed
college students, no significant differences were found in

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depression levels after seven weeks of group psychotherapy
with and without AAA.60 Unlike previous studies with
dogs, an investigation on the effect of aquarium presence on
psychiatric patients’ depression, fear, and frustration
revealed no benefit, although a trend toward reduced
anxiety was observed.61

Other studies have focused specifically on AAA in patients
diagnosed with schizophrenia. Although sample sizes were
small, studies have reported improvements in increased
hedonic tone and use of leisure time,62 involvement in
domestic and health activities,63 nonverbal communica-
tion,64 and social functioning65 with AAA.

Collectively, these studies provide some evidence of
improved mood and increased social behavior associated
with AAA in those with psychiatric disorders. Such
preliminary results warrant further investigation.

A few studies have targeted samples of health care pro-
fessionals. Researchers in one descriptive study found that
therapists who incorporate therapy dogs into their psy-
chotherapy practices perceive this approach as an effective
technique that can benefit clients with a wide range of
clinical problems and in various age groups and practice
settings.66 In another study, therapists who had a dog
present were rated more favorably by college students than
those without a dog.67 Other researchers have looked at the
effect of AAA on measures of psychoneuroimmunology in
health care professionals in a repeated-measures crossover
study.68 They found a significant decline in both serum and
salivary cortisol levels that was detectable after 45 minutes
following as little as five minutes with a therapy dog.
No significant effects were found on immune function.

Benefits of AAA for Nursing-Home Residents and
Seniors with Dementia
Studies addressing the benefits of AAA for nursing-home
residents have primarily assessed outcomes of mood, daily
functioning, and social interactions using various measures
and designs. An anthropological study concluded that
residents perceive visitors with pets as facilitating a sense
of domesticity.69 A randomized, pre-/post-intervention,
control group study comparing the effects of AAA and
human visits reported no differences on depression, but
AAA improved mood as measured by the profile of mood
states (POMS).70 A longitudinal Australian study compar-
ing a resident dog, visiting dog, and visiting researcher
reported improved POMS scores in the resident-dog
group over the other groups for tension, confusion,
and depression, with both dog groups showing reduced
fatigue.71 Others have found reduced depression in
nursing-home residents provided with a companion bird
for 10 days.72 While no association was noted between the
presence of an aviary and reduced depression for elderly
males in a health care day program, reduced depression was
found in those who utilized the aviary.73

Using a wide range of measures to compare the effects of
AAA with usual nursing-home activities in Torino, Italy,
researchers found AAA to be associated with BP reductions,
but not with measures of illness, depression, or daily
activities, or with mental or nutritional status.74 Other
studies with nursing-home residents have reported positive
outcomes associated with AAA. In one study, nursing-home
residents who were randomly assigned to one or three

weekly individual AAA sessions over six weeks were found
to have decreased loneliness with one AAA session a
week.75 In a follow-up study over the same time frame, the
same investigators compared AAA in an individual versus
group format, and found reduced loneliness following
individual AAA with no benefit in the group format.76

AAA has been found to enhance social behavior in several
studies of loneliness among nursing-home residents.77–79

Increases in interactive behavior were also found six weeks
following the introduction of a resident dog in another
study; however, residents’ behavior returned to baseline
after 22 weeks.80 A within-subjects observational study
of nursing-home residents visited by people alone, pets
alone, and people and pets, found that all conditions were
associated with increased smiling and alertness, but the
greatest number of positive behaviors was associated with
close proximity to the person alone.81

Focusing on geriatric patients with cognitive impairments,
including dementia and Alzheimer ’s disease, researchers
have reported several benefits associated with AAA with
dogs, including reduced HR and unit noise,82 reduced
agitation and increased social interaction,83 increased social
behaviors,84,85 reduced use of physical restraints, increased
orientation to time, and facilitated goal achievement.86 AAA
with dogs and cats has also been reported to decrease
aggressiveness, anxiety, and phobias in elderly patients with
Alzheimer ’s disease, and to reduce caregiver burden.87

Patients with Alzheimer ’s disease who ate in front of
an aquarium daily for eight weeks were found to have
increased nutritional intake and weight gain,88 while
another study found the presence of a companion canary
compared with having a plant improved a range of
psychiatric symptoms and perceived quality of life after
three months.89

Not all studies have reported benefits of AAA for those with
cognitive impairments. A single AAA experience had no
effect on agitation, socialization, or dementia in one study of
28 residents in extended-care facilities,90 and no effect on
mental status, depression, self maintenance, or irritability
was found after four days of AAA in eight patients with
dementia.91 Collectively, however, these studies support the
association of beneficial effects with AAA for patients with
Alzheimer ’s disease or dementia, and call for more rigorous
research with this population. While not affecting cognitive
status, AAA may provide some benefits to mood, loneliness,
socialization, and problem behaviors.

Benefits of AAA for Children
Most studies of AAA with children have focused on clinical
populations. However, one crossover study of Native
American preschool children who were randomly assigned
to brief, bi-weekly AAA sessions with various pets showed
no social-skills benefit from AAA, but decreased absences
during the first six weeks of the program.92 Other
researchers have reported that the presence of a friendly
dog reduced BP in children who were reading aloud or
at rest.93

A number of studies have evaluated the benefits of AAA for
children in health care settings, with mixed results.
Descriptive studies report satisfied parents and staff.94

However, a dog’s presence during a dental procedure did
not reduce school-age children’s behavioral distress or

490 JVME 35(4) � 2008 AAVMC



physiological arousal.95 One study of young children
undergoing a physical examination in a pediatric clinic
found no difference on physiological measures of arousal in
children who were randomly assigned to the presence of a
dog, although less behavioral distress was reported.96

In contrast, positive outcomes were reported in a within-
subjects study of a dog’s presence during the routine
physical examination of preschool children.97 The presence
of a dog was associated with reduced SBP, mean arterial
pressure, HR, and distress. Focusing on pain perception in
post-operative children, another study reported that AAA
was associated with less perceived physical and emotional
pain.98

Several small studies have explored the effects of AAA on
children with developmental disorders. One observational
study of 12 autistic children noted fewer autistic and more
socially appropriate behaviors during therapy with a dog;
however, these gains declined after one month of follow-
up.99 Using llamas, dogs, and rabbits in occupational
therapy with 22 autistic children, researchers reported an
increased use of language and social interaction with AAA
compared to with traditional occupational therapy.100

Another study measuring social outcomes was conducted
with 10 children with pervasive developmental disorders.
These children were rated as being more aware of their
social environment, more focused, and more playful during
AAA with a dog.101 Other studies involving very small
samples of patients with a variety of developmental
and emotional disorders have reported various benefits of
AAA, including more sustained focus;102 emotional
stability, improved attitudes toward school, and improved
learning in responsibility, respect, and empathy;103 progress
on individual goals;104 and sociability, vocal expression, and
eye contact.105

One explanation for the benefits found in children with
special needs is provided by Katcher in his rationale for
including AAA in the form of an AAT/education (AAT/E)
program for children with attention deficit/hyperactivity
disorder (ADHD) and conduct disorder.106 Katcher con-
tends that the innate tendency to pay attention to nature and
animals may increase a child’s ability to inhibit responses, a
critical deficit for children with ADHD and other disorders.
However, as Katcher found in his well-designed evaluation
of the AAT/E program at Devereux in West Chester, PA,
context is an important variable since positive behavioral
outcomes noted in the AAT/E context did not generalize to
the regular classroom.

Most of the published AAA studies are descriptive and
based on convenience samples. While inconsistencies in
results abound, there seems to be some agreement on an
association between AAA and improvements in mood for
certain populations. Support for a positive impact of AAA
on depression comes from a recent meta-analysis of five
experimental studies that reported medium and significant
aggregate effect sizes indicating that AAA is associated with
fewer depressive symptoms.107 The studies included in this
meta-analysis met criteria for methodological rigor, and the
results provide important evidence for a benefit of AAA in
those with depressive symptoms. In addition, AAA shows
potential for improving CV reactivity to stress and for
improving mood and social behaviors in nursing-home and

psychiatric patients, including those with Alzheimer ’s
disease and other dementias.

DISCUSSION
One of the earliest reviews of research on the benefits of
human–companion animal interaction was conducted in
1984 by Beck and Katcher.108 They noted the preponderance
of descriptive studies and identified only six experimental
studies published at that time, which reported little or no
benefit of pets. The current review reflects considerable
progress since that time, with the review of 129 studies
published in peer-reviewed journals. Like the 1984 review,
most of the research continues to be descriptive and, while
providing valuable information for generating research
hypotheses, lacks the necessary controls to enable us to
determine whether benefits actually result from pet owner-
ship or AAA. However, a number of strong studies
contributing to the field have been presented, including
large surveys of nationally or regionally representative
samples. A number of these studies used existing databases
(e.g., Medicare) or included pet-related variables in non-
pet-focused studies (e.g. CAST, Health ABC Study). The
series of studies by Friedmann et al investigating pet
ownership and mortality have contributed significantly to
the field,1–3 as have the large Australian surveys on pet
ownership and CV risk factors and/or health conducted by
Anderson et al,4 Parslow et al,5,16 Pachana et al,17 Schofield
et al,29 and Headey et al.6,7 In North America, large-scale
studies on the health benefits of pet ownership by Thorpe
et al,27 Raina et al,28 Brown and Rhodes,30 Siegel et al,36,109

and Tucker et al110 have added to our knowledge of the
benefits for varied populations.

As evident in this review, considerably more experimental
studies have been published since the six identified by Beck
and Katcher in 1984.108 While the majority have been
conducted on relatively small numbers of convenience
samples, several are noteworthy for their methodologies:
Banks and Banks’ replication of their earlier pre-/post-
intervention, control-group study, again finding decreased
loneliness in long-term care residents who were randomly
assigned to individual AAA sessions for six weeks, with no
benefit for AAA delivered in a group setting;75,76 Barker
et al’s partial replication of a pre-/post-intervention, cross-
over design of AAA with electroconvulsive therapy patients
finding significant reductions in fear after AAA with a
therapy dog but not in the presence of an aquarium;54,61

Allen et al’s random assignment of 48 hypertensive stock
brokers beginning ACE-inhibitor therapy to pet ownership
with a wait-list control group, finding pet ownership was
associated with reduced CV reactivity and improved mental
task performance;22 Columbo et al’s pre-/post-intervention,
control-group study involving the random assignment of
144 cognitively impaired nursing-home residents to three
months with a plant, canary, or control, and reporting
improved scores on measures of psychopathological status
and quality of life for the canary group;89 and Edwards and
Beck’s time-series study finding increased caloric intake,
increased weight, and less need for nutritional supplements
in dementia patients who ate their meals in front of an
aquarium.88

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Finally, a few studies have begun to look at physiological
mechanisms that may explain the benefits of interacting
with companion animals. Both Allen et al21–23 and
Friedmann et al3,47 have looked at CV mechanisms, while
Barker et al68 have investigated psychoneuroimmunological
mechanisms.

This review has summarized many studies on the benefits
of human–companion animal interaction. Both clinical and
non-clinical samples attest to the perceived benefits of pet
ownership and AAA, and the number of controlled studies
supporting such claims is growing. Most have measured
short-term outcomes, and studies of the long-term effects of
human–animal interactions are needed to determine
whether the short-term benefits are maintained over time.
The studies published so far vary greatly in subject samples,
interventions, outcomes, procedures, and instruments,
making it difficult to make comparisons and draw conclu-
sions. Indeed, categorizing the published studies for this
review represented a challenge, with few lines of research
focusing and building on a common area of inquiry.
As already noted, a number of these studies reported
conflicting findings, which served to clarify the important
distinction between research methodologies that limit
their interpretation of results to associations and those that
establish causation, designs that limit generalization to
specific populations (e.g., males, the elderly) and/or
locations (e.g., psychiatric hospitals, nursing homes), and
the need to identify and control for factors that might
explain the results. It is clear that more rigorous research,
grounded in theoretical models, is needed to support
descriptive studies claiming benefits of human–animal
interactions. Randomization and control conditions are
needed, as are clear descriptions of interventions to enable
replication studies. More consistent use of standardized
instruments that have been shown to be sensitive to the
effects of human–animal interactions will also improve
our ability to compare study results and draw firmer
conclusions. For evidence-based benefits of pet ownership
or AAA, exploration of the underlying physiological
mechanisms of action is needed.

Despite these factors, a few pockets of evidence do exist and
appear to be growing. Pets appear to buffer the impact
of stress on some owners, and may be associated with
other health attributes such as increased physical activity
for some owner groups. Seniors in nursing homes and
those with Alzheimer ’s disease or dementia appear to
benefit from both pet ownership and AAA in the areas of
mood, loneliness, social behaviors, and caloric intake.
Similarly, some psychiatric populations also appear to
benefit from AAA in terms of improved mood and social
behaviors. Finally, there is emerging evidence of the possible
benefits of pet attachment for children, particularly with
regards to empathy, and of AAA for children with special
needs.

Finally, readers will have noted the great variation in
research foci of the investigators whose works are included.
Whether this reflects varied research interests, lack of
consistent research funding available in the field, institu-
tional constraints, or other variables, this review illuminates
the need for a more clearly defined direction in future
research to systematically investigate the benefits of
interacting with companion animals.

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2 Friedmann E, Thomas SA. Pet ownership, social
support, and one-year survival after acute myocardial
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AUTHOR INFORMATION

Sandra B. Barker, PhD, is a Professor of Psychiatry and
Director of The School of Medicine Center for Human–Animal

Interaction, Virginia Commonwealth University, P.O.

Box 980710, Richmond, VA 23298 USA. She is also Adjunct

Professor of Small Animal Clinical Sciences at Virginia-Maryland

Regional College of Veterinary Medicine.

E-mail: sbarker@mcvh-vcu.edu.

Aaron R. Wolen is a graduate of the University of Iowa with a

BS in psychology and a minor in biology. He is currently

pursuing a PhD in human genetics at Virginia Commonwealth

University’s School of Medicine, P.O. Box 980710, Richmond,

VA 23298 USA, where he completed a research assistantship

with the Center for Human–Animal Interaction.

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