Most studies of pet ownership are descriptive, with data collected primarily from interviews and surveys of convenience samples, thus making them difficult to compare 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 unit
1 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.
3Several 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 representative sample randomly selected for inclusion in a longitudinal health study.
Another large (n=1,011) 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 approximately 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 maintaining improved levels of health and morale in a longitudinal 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 crossover 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 ownership 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 recipients 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 relationship 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.
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.
34A 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 (n=2,551) 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 (n=1,872) participating in the Multicenter AIDS Cohort Study.
36Several 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 morale
37 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 observational 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 competence 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.
44These 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.