Another in five of the six aforementioned

Another area of
research that has mostly been overlooked is the impact humans have on an
animal’s hormones, very few experimental studies attempt to quantify what
happens inside a dog’s physiology during HAI. One such study examined the
impact HAI had on ?-endorphins, ?-phenylethylamine, oxytocin, prolactin,
dopamine, and cortisol in both humans, pet dogs, and unfamiliar dogs (Odendaal
2000; Odendaal & Meintjes 2003). Following a positive interaction between a
human and their companion dog, there was a significant increase in five of the
six aforementioned parameters for both species, however, cortisol only
decreased in humans. A further analysis of oxytocin levels between conditions
indicated a stronger increase in hormones when petting one’s own dog as
compared to an unfamiliar dog. This suggests that when a stronger bond is
formed between human and animal more oxytocin is released. Handlin (2011)
performed a similar experiment with female dog owners and their male Labrador
Retrievers in which they sought to measure heart rate, oxytocin, cortisol, and
insulin across species. They anticipated that oxytocin would be released in
both the dog and its owner after a brief three-minute tactual interaction, and
the effects, such as lower heart rate, would continue well after the interaction
ended. Their hypothesis was supported in that peak oxytocin levels were
recorded during and shortly after the HAI, and heart rate was still lowered 55
minutes after the interaction. Likewise, cortisol levels showed a marked
decrease 15 and 30 minutes after HAI in humans, but cortisol levels in dogs
showed an increase at comparable times. There was no significant change in
insulin levels throughout this experiment.

While more
research in the area of interspecies interactions is need to understand
potential health benefits for companion animals, there remains no shortage of information
on the physical effects pets have on the human body. A vast number of studies
have documented how HAI can have a positive effect on our cardiovascular
system. Kaminski, Pellino, and Wish (2002) demonstrated this in a study with 70
hospitalized children when they were assigned to either play therapy or AAT.
Both types of therapy had an enhancing effect on mood, but it was only when the
children played with a therapy dog that their heart rate was significantly
lowered. Another study compared children when they were in the absence or
presence of unfamiliar dog during a routine physical examination which served
as a natural stressor (Nagengast, Baun, Megel, 1997). There was
a significant decrease in systolic blood pressure (SBP) and heart rate when the
dog was present. Friedmann, Katcher, Thomas, Lynch and Messent (1983) found
comparable results when looking at the introduction of a dog at the beginning
or in the second half of their experiment where participants were either
reading or resting. The presence of a friendly dog resulted in lower blood
pressure and heart rate in both conditions, and the effect was strongest when
the dog was present from the beginning. As the researchers suggest, it is
possible that having an animal present for a potentially stressful situation
allows the participant to modify their perception of the event, ultimately
making it less threatening.

Having a companion
animal present may reduce autonomic reactivity by allowing a human to perceive
a situation as less stressful, but this effect may also happen because pets are
nonevaluative. As discussed previously, Allen et al. (1991) examined the idea
of evaluative verses nonevaluative others on stress and task performance. This
study not only found the presence of a nonevaluative companion, in this case a dog, is more beneficial for task
performance during a serial subtraction task, but they found those in the
pet-present condition had notably less autonomic reactivity than those in the
friend-present condition. Moreover, skin conductance, blood pressure, and pulse
rate were significantly lower in the pet-present condition than when
participants underwent the task alone. Ten years later, another experiment investigated
how acquiring a pet would affect stockbrokers diagnosed with stage II
hypertension (Allen, Shykoff, & Izzo, 2001). In this study, all 48
participants were assigned to take 20mg/d of Lisinopril, a drug used to treat
high blood pressure, and half of them were assigned to acquire a companion
animal while half were not. Measurements of blood pressure, heart rate, and
renin responses were evaluated before and after the acquirement of a pet and
drug therapy during speech and mental arithmetic stressors. Results expressed a
significant drop in all three parameters
in the pet group compared to the non-pet owner group. Improved task performance
was also positively correlated with pet ownership, continuing the idea that
animal companions may indeed be viewed as a form of nonjudgmental social

As previous
studies have shown, having a pet present for a stressful task or a natural
stressor tends to reduce the impact of the physiological stress response. Now
we will examine studies that emphasis the importance of tactual HAI as one of
the key factors in what makes interspecies bonds so beneficial for health. Grossberg
and Alf (1985) designed an experiment in which participants heart rate,
systolic and diastolic blood pressure, and mean arterial pressure were measured
when they were randomly assigned to rest, converse, read, or pet a dog. Results
revealed a significant lower heart rate and blood pressure for the resting
condition when compared to the other three conditions, and yet blood pressure
was significantly lower when petting a dog than when reading or conversing.
Once again, there was a correlation between positive pet attitudes and lower
cardiovascular response such that more favorable attitudes coincided with lower
physiological arousal. A few years later, Vormbrock and Grossberg (1988)
attempted to determine if touch was the major factor that contributed to
cardiovascular benefits for humans. They collected a sample of undergraduate
students to interact with a dog by way of touch, verbalization, or visual
gazing. Blood pressure was found to be at its lowest when petting the dog and
heart rate was lowest when conversing, and unsurprisingly, blood pressure was
highest when talking with the experimenter. Another study reported similar
results in that those who stroked their companion dog had significantly
decreased blood pressure compared to when they were asked to read aloud
(Jenkins, 1986). Subsequent studies have also reported tactual HAI to be
beneficial even if the companion is not a dog. DeMello (1999) investigated physiological
recovery time from cognitive stressors in the presence of traditional and
nontraditional pets. Two small dogs and a kid goat were used for this
particular experiment. Fifty participants underwent three, five-minute
assignments – mental arithmetic, coding, cancellation tasks – during which the
pet was present but only visual contact was permitted, pet was present and
petting was permitted, or pet was absent. Their hypothesis that blood pressure
and heart rate would be significantly reduced in the presence of a pet was
supported, however only heart rate was lowered when petting the animal, blood
pressure was not significantly affected.

Lastly, Allen,
Blascovich, and Mendes (2002) assessed psychological and physiological
stressors on cardiovascular reactivity when participants were in the presence
of their spouse, a friend or a pet, or alone. Two-hundred and forty middle-aged,
married couples participated, half of which owned a pet,