Background
Dating back to 32,000 years ago, the process of domestication of dogs began in Eurasia from grey wolves and about 10,000 years ago in the Near East domestication of cats began (Amiot, 2016). In the United States, over half of the population owns a dog and/or a cat. Specifically, it has been found that about 75 million Americans own a dog and roughly 35% of Americans own a cat (Urbanik, 2013). Furthermore, it is extremely common for children to grow up in a household with a pet. It is so common that “children are more likely to live with a pet than live with their biological father or a sibling” (Reaser, 2008).
The close relationship between pets and humans has been studied to determine if animals provide physical and psychological benefits to humans as well as longevity. The health benefits humans experience from human-pet interaction is known as the “pet effect.” Specifically, the beneficial health effects that occur from humans living with their pet (Herzog, 2011). For example, living with an animal has found to decrease blood pressure, lower cholesterol, and increase an individual’s mood. Furthermore, the special bond between humans and pets has been hypothesized to occur due to a phenomenon known as biophilia. This term was coined by Dr. Edward O Wilson and directly means “love of life or living systems” (Abel, 2017). Biophilia can be defined as the human tendency to connect with nature or other forms of life. Simply, it can be understood as the natural pleasure that arises when surrounded by animals and other living organisms.
Throughout history the tendency for humans to interact with nature can be understood. Dating back to roughly 550 B.C, Persian settlements and Chinese villages were known for elaborate and detailed gardens in order to maintain close contact with nature. In the last 200 years, there has been a great increase in the number of parks and national reservations. This is due to the belief that nature has a direct impact on psychological well-being and a decrease in stress (Ulrich, 1993). The national parks are crowded with people each year to observe the breathtaking nature. As of 2021 in the United States, there are 423 national parks and roughly 237 million people visit the parks each year (Runte, 2021). Furthermore, humans are fascinated with seeing and viewing other living organisms such as those in zoos. A research study found that in the United States and Canada, the number of children and adults that visited zoos was much greater than those who attend professional sporting events combined (Wilson, 1993). This idea relates to the hypothesis of biophilia as humans are benefiting from interacting with different forms of nature. In Figure 1 below various national parks throughout each state in the US can be observed.
Figure 1. National Parks in the United States
Introduction
In most societies across the world, pet keeping is a common practice. However, the reasoning behind pet keeping is not completely understood. The cost of dogs and cats can be expensive as the average cost world-wide ranges from $8,000-$10,000 depending on the size, breed, and longevity of the animal. Another factor that makes pet keeping difficult to understand is that pets can cause extreme harm to their human owners. For example in the United States, 85,000 people are sent to the emergency room each year due to falls caused by their pets. Furthermore, it has been found that “a person is 100 times more likely to be seriously injured or killed by a dog than by a venomous snake” (Herzog, 2011). Another danger pets entail is they have the ability to spread disease to humans including E. coli, cat-scratch fever, and ringworm (Herzog, 2011). Approximately 5 million people are bitten by dogs per year, further increasing the risk of spreading zoonotic diseases (Ghasemzadeh, 2015). Therefore, these negative effects of owning a pet make it difficult to truly understand why pet keeping is so popular worldwide. But there are many hypotheses including biophilia, companionship, and protection that help researchers understand why humans and animals share a special bond. Additionally, studies have found that human and pet interaction can increase mood, decrease blood pressure, and relieve stress and anxiety.
Many studies and experiments have been conducted in order to examine the relationship between pets and the effect they have on their owners physical and mental health. However, there has been a lot of differing results such as studies that have shown positive correlation, no correlation, and even negative correlation between pet interaction and human health. For example, an experiment displayed the benefits that pets have on their owners health. The study consisted of 92 heart-attack victims and found that those who owned a pet (type of pet was unspecified) had a higher chance of survival of a year or longer. Specifically, 28% of the victims who owned a pet survived for at least a year while only 6% of those who did not own an animal survived longer than a year (Friedman, 1980). Another study was done to evaluate the effect that pets have on an individual’s blood pressure and stress level. During the experiment, hypertensive stockbrokers were selected as the participants and they were either assigned to either a pet or no pet. After six months, the stockbrokers were placed in a highly stressful situation. It was found those who were given a pet displayed lower increases in blood pressure compared to those who did not receive a pet (Allen, 2001).
Additionally, another research study was done over the span of 10 months in order to observe long term effects that pets have on humans. The experiment consisted of 71 adult subjects who were observed after getting a new dog or cat in order to monitor any changes in their behavior or health status. Of the 71 subjects, 47 were dog owners and 24 were cat owners. Furthermore, a control group of 26 subjects without pets were used to compare pet owners versus non pet owners. The data showed no significant data for the control group. As for the pet owner group, the subjects experienced a significant decrease in minor health problems during the first month of owning a dog or cat. However, those that owned a dog sustained the health benefits throughout the entire 10 months. The pet owner group was also found to have significant improvement in their psychological well-being. Again, the dog owner’s improvement lasted 10 months compared to the cat owners who did not necessarily have the same effect for the full 10 months (Burger, 1990). Thus, the researchers concluded that pets have a positive impact on human health over a long period of time rather than the immediate effect following the pet interaction.
Pets can also positively impact human health as they encourage physical activity. Specifically, dogs as they are commonly taken on walks and sometimes multiple walks per day. Another circumstance that benefits human health by pets is known as the social catalyst effect. This effect is when humans become more social with other individuals after interacting with an animal. Similarly, an experiment was conducted to see what makes somebody more approachable in public. A female experimenter was placed in six different conditions while 1800 strangers passed her. The conditions included the female joined by “a Labrador retriever pup, by an adult Labrador, by an adult Rottweiler, being in the presence of a teddy bear or a plant, or being alone as control conditions” (Beetz, 2012). The data showed that the experimenter was ignored the most when she was by herself and given a little more attention when in the presence of the teddy bear or plant. But she received the most attention (smiles and verbal responses) in the presence of the Labrador puppy and adult Labrador (Beetz, 2012). Therefore, the study concluded that interacting with pets influences humans to interact with other individuals. Likewise, other individuals are more likely to engage in social interactions when a dog is present. Thus representing that the pets had a positive effect on human health.
In addition to pets having a positive impact on human’s physical and psychological health, pets are also used for therapeutic purposes. This is what is known as animal-assisted intervention (AAI) and it encompasses animal-assisted therapy (AAT), animal-assisted activities (AAA), and equine-facilitated programs. AAI can be defined as “any intervention that intentionally includes or incorporates animals as part of a therapeutic or ameliorative process or milieu” (Fine, 2006). Also, AAI is a type of therapy that uses animal interactions to help someone recover from a health problem or to help one cope with various mental disorders. Throughout AAI literature it is thought that the mere existence of animals, their spontaneous actions, and their availability for interaction can provide opportunities and benefits that would otherwise be unlikely or much more difficult in the absence of animals. A disorder that is often investigated through AAI is autism spectrum disorder (ASD). Typically those who suffer from ASD experience a deficit in social communication, repetitive behaviors, and are often times more irritable. A study was conducted to test the hypothesis that those diagnosed with ASD would benefit from interacting with animals and decrease their symptoms. The study consisted of 31 subjects aged 8-14 years old. The experimental group was given an animal but the control group did not receive an animal. Both groups were monitored over the span of 12 weeks using weekly social skills training and treatment. Following the 12 experimental weeks, the group that was given the dogs were shown to be significantly less symptomatic than the control group using the Social Responsiveness Scale (SRS-2). Furthermore, self rating was conducted using the Children’s Depression Inventory (CDI-2). The results also expressed that the participants in the experimental group with dogs had a significant reduction in their symptoms compared to the control group. Overall, both groups experienced a decrease in loneliness and depressive symptoms. However, the control group data over the span of the 12 weeks was found to be insignificant (Seda, 2020). Although that experiment showed a positive impact from dogs on those diagnosed with ASD, many other AAI studies have found to be inconclusive. Therefore, most researchers suggest that more studies need to be done as many were found to be contradictory.
On the other hand, there has been data that shows no correlation between human health benefits and pets. Particularly a study was done in England where researchers hypothesized that pets would decrease loneliness and increase an individual’s mood. Individuals that were looking to get a companion animal were given the UCLA-Loneliness scale to determine the level of loneliness the individual was experiencing. After six months the participants were given the test again to see how the results differed. However, it was found that the participants were just as lonely after owning an animal for six months than they were before and they were no happier than those who did not get a pet (Gibey, 2007). Similarly, a study was done to determine if pet owners have lower blood pressure than non-pet owners as well as if they are at a lower risk of hypertension. There were 1,179 participants but the data showed no correlation between pet owners and lower blood pressure or a lower risk for hypertension (Wright, 2007).
Furthermore, there has been research that shows a negative correlation between human and pet interaction. A study of 40,000 Swedes was performed and found that the participants that owned a pet were physically more healthy than those who did not own a pet. But, the pet owners were also found to suffer from more psychological disorders such as anxiety, depression, and insomnia (Miillersdorf, 2010). Similarly, another study was done to compare depression in individuals who owned a pet versus those who did not. However, the research found that those who owned a pet were actually more depressed due to their attachment to their companion animal than those who are not pet owners (Miltiades, 2011). Therefore, both studies concluded that pets actually have a negative effect on their owners health. However, due to inconsistencies in positive correlation, no correlation, and negative correlation of pets effect on humans health, it cannot be confirmed or denied the impact that animals have on humans.
Therefore, the conflicting data makes the research inconclusive. Reasons for the varying data have been hypothesized to have resulted from design flaws and due to the use of small and homogenous sample sizes when evaluating human-pet interaction. Researchers have also stated that it is very difficult to differentiate the data between pet owners versus non-pet owners (Ioannidis, 2005). Another limitation is the use of self-reported data which is often used in studies to evaluate the relationship between pets and human health. For instance, a study used a self-report test for individuals suffering from chronic fatigue syndrome. The participants obtained a pet in order to evaluate if their pet provided psychological and physical benefits. The researcher found that the pet owners reported their pets to have a positive impact on their health but their scores on the Chalder Fatigue Questionnaire, the General Health Questionnaire-12, and the Short Form-37 Health Survey were found to contradict the owners self report. The scores indicated that the participants were just as depressed, tired, and worried as those who did not receive a pet (Wells, 2009).
Although many studies have been performed, more research is necessary to confirm or deny the pet effect on human health. Many of the previous studies are now outdated and new studies should be conducted in order to test the hypothesis that pets have beneficial effects on pet owners. With that being said, there was a recent study conducted in 2019 that explored the role of oxytocin in both pets and humans after a positive interaction with each other. Oxytocin is a hormone that is associated with an increase in mood and its function is to stimulate social bonding, relaxation, and ease stress. The researchers hypothesized that both the dog and human’s oxytocin levels would increase after a positive interaction with a dog that is closely bonded to its owner. However, the data did not support the hypothesis and there were many variables that played a role in the concluding data. Due to the uncertainty in the data, the researchers suggested performing more experiments to further investigate the role of oxytocin during human-pet interactions. Also, the researchers believe a greater standardization of methods is necessary (Marshall-Pescini, 2019). Therefore, the recent experiment emphasizes the importance of continuing to study the phenomenon of pets and human health due to conflicting experimental data and potential publication bias.
Sommerville Study
In 2008 John Sommerville and his colleagues conducted an experiment to evaluate the effect that pets have on blood pressure and heart rate from male and female college students. The study consisted of two phases. The first phase included a one page survey that asked students to check a box if they like cats, do not like cats, or do not like or dislike cats. Similarly the same three questions were asked for dogs. Then the participants were asked to check “yes” or “no” if they own a dog or cat or if their parents own one. However, participants were rejected from the study if they had pet allergies, a fear of dogs or cats, or if they had chronic hypertension. Once the participants were deemed eligible for the study, they were moved to phase two which consisted of 62 individuals. Phase two included 10 blood pressure and heart rate readings per participant using a digital blood pressure cuff. One reading was taken at the beginning of the experiment and another was taken at the end of nine 5-minute intervals. During the third and seventh 5-minute interval, the participants were given either a dog or one of the two cats to hold for the following five minutes while alternating the dog or cats. Throughout the experiment blood pressure and heart rate was taken at various times to ensure the researchers had a baseline reading without the presence of an animal and potential differences in the readings when holding an animal (Sommerville, 2008).
After evaluating the data, the researchers averaged the baseline measurements as there was very minimal difference between the three baseline readings. Because there were two different cats being used, a t-test was used to observe any differences in the measurements but there was found to be little difference so the data for the cats were combined. Furthermore, the results indicated that the data was not statistically significant for changes in blood pressure and heart rate when holding a dog versus a cat. The results were also found to not be statistically significant for participants holding an animal. However, there was found to be a significant decrease in diastolic blood pressure immediately after holding the dog or one of the cats (Sommerville, 2008).
Methods
The research conducted in this experiment used a similar study to the Sommerville experiment. However, this experiment only consisted of one phase rather than the published study that contained two phases. The overall goal of this study was to evaluate the effect that pets have on human health. Specifically, to determine if pets have a positive effect on human health by decreasing human’s blood pressure and heart rate. It was hypothesized that pets would decrease both human’s blood pressure and heart rate.
The experiment consisted of 35 participants with 20 females and 15 males with ages ranging from 20-50 years old. In order to measure the participants blood pressure and heart rate, a digital blood pressure cuff was used as it also had the ability to measure heart rate. The participants were either taken to the Bloomington animal shelter, Anthony’s pet shop at the college mall, or the participants could remain in their individual home if they had a dog or cat of their own. The participants were given the choice to interact with either a cat or dog depending on their preference. But before the interaction with the pet, the participants’ blood pressure and heart rate was recorded in an Excel spreadsheet. The participants systolic blood pressure and diastolic blood pressure were recorded separately for comparison. Then the participants interacted with the animal of their choice for roughly 15 minutes and their blood pressure and heart rate was recorded again afterwards.
When all of the data was collected, three paired t-tests were used to evaluate two measurements from the same person in order to determine whether or not the results were significant. The three paired t-tests included one for the systolic blood pressure, one for the diastolic blood pressure, and one for heart rate. When conducting a paired t-test there is a null hypothesis and an alternative hypothesis. The null hypothesis assumes that the true mean difference between the paired samples is zero. The two-tailed alternative hypothesis assumes that the true mean difference is not equal to zero. Then a critical value (p) of 0.05 is used to determine if the null should be rejected or if the data fails to reject the null. If the p value is less than 0.05 then the null hypothesis is rejected and the data is said to be statistically significant. On the other hand, if the p value is greater than 0.05 then one fails to reject the null hypothesis and the data is not significant.
In Figure 2 below, an image of a participant interacting with his cat is displayed. As seen in the image, the participant is wearing a blood pressure cuff to measure his blood pressure and heart rate before and after playing with his cat for 15 minutes.
Figure 2. Participant Interacting with Cat While Monitoring Blood Pressure/Heart Rate
Results
At the beginning of the experiment each participant’s blood pressure (both systolic and diastolic) and heart rate were recorded. The typical systolic blood pressure ranges from 90 to 120 and the average systolic reading for the participants was approximately 113. The normal range for diastolic blood pressure is commonly found between 60-80 and the participants average was 76. As for heart rate, the normal range is 60 to 100 beats per minute (bpm) and the mean was found to be 77 bpm. After the participants interacted with a dog or cat for 15 minutes, the three measurements were taken again. Following the subjects playing with various pets, the average systolic blood pressure was 112, the diastolic was 76, and the heart rate was also 76 bpm. Although there was little difference before and after pet interaction, three t-tests were performed to determine the significance of the data. The p value of the systolic blood pressure had a value of 0.2136 therefore indicating that there is no statistical significance. The diastolic pressure had a p value of 0.3823 and the heart rate had a p value of 0.1697 thus indicating that the data was not statistically significant. There were also minimal differences in the three measurements when comparing those who interacted with dogs versus cats.
Additionally, it was noted if there was a difference in participants that interacted with their own animal whom were familiar with versus a random animal at the shelter or pet store. There were 10 participants that had a pet of their own and those that played with their own pets had an average of 115 for their systolic blood pressure before interacting with their pets. The diastolic blood pressure had a mean of 74 and the heart rate averaged at 75 bpm. After interacting with their own animals, the average systolic decreased to 108, the diastolic decreased to 70, but the heart remained roughly the same at 76 bpm.
Discussion
Similarly to the Sommerville study, there was found to be no significant difference between systolic and diastolic blood pressure as well as heart rate. The first p value of 0.2136 is greater than 0.05 leading to the failure of rejection of the null hypothesis. Similarly for the p values of 0.3823 and 0.1697, they again lead to the failure of rejection of the null hypothesis. The failure to reject the null hypothesis implies that it cannot be confirmed that pets have a direct effect on the decrease in blood pressure or heart rate.
Although the data was found to be insignificant, a majority of the individuals seemed to have a shift in their mood after playing with cats and/or dogs. Oftentimes the participants mentioned that they were stressed due to school especially near finals week or with work so taking a break to go play with different animals was refreshing. Below in Figure 3 there are multiple images that were obtained throughout the semester that show the interaction of various participants with different animals. In each of the photos the overall emotion is happy and cheerful with both cats and dogs.
Figure 3. Participants Interacting with Animals
During the experiment, there were multiple limitations that may have affected the results. Due to COVID restrictions, the Bloomington shelter would only allow visitors if they made an appointment. But the coordinators strongly emphasized that they only wanted visitors making an appointment if they were serious about adopting a pet therefore limiting the places the participants could visit. Another limitation was the amount of participants that were in the study. Due to corona and the length of time given, it was difficult to get a large sample size of participants which could affect the significance of the data.
The results from the experiment indicate that pets do not have a correlation to effecting human health. Thus, leading to the need for further studies to be conducted as many studies have given mixed results. In the future if the experiment were to be conducted again, multiple factors should be taken into consideration. Possible reasons for contradictory results are due to various methodologies that have been used, self reported data, and small, homogenous sample sizes. In regards to this experiment, many other outside factors should be taken into consideration as well. For example, the age and sex of participants should be considered as males has been found to have higher blood pressure than females, similarly for people of older age. In addition, family history should be examined as individuals may be more susceptible to higher or lower blood pressure and heart rate. It would also be beneficial to compare smokers versus non-smokers to observe if there is a big difference in their measurements. Lastly, it would be helpful to calculate the amount of exercise that the participants partake in as more exercise can lead to a chronic decrease in heart rate.
Conclusion
Overall the data was found to be statistically insignificant however, research on human and animal interaction should be extensively studied in the future. A lot of research has shown that pets have a positive impact on human health. For instance, a decrease in anxiety, a decrease in blood pressure, and an increase in mood due to an increase of oxytocin. However, other studies have found no correlation between human and pet interaction and some studies found a negative correlation between the two. Research has found that animal companionship can lead to an increase in depression for pet owners as well as an increased risk of spreading zoonotic diseases. Therefore, the contradictory statistics emphasize the need to further study human-animal interaction as it could be beneficial or detrimental to human health.
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