Public health traditionally has focused on animals in terms of environmental health, reflecting concerns that they may serve as vectors of disease. Yet research has offered little evidence of pets as significant contributors to human disease [1,2,3]; rather, it has been suggested that pet ownership may be beneficial in promoting health outcomes [4, 5]. While Beck and Meyers [6] concluded that research on the benefits of animal companionship to public health was needed, little has been done in the United States to move this work to the population level.
To provide a public health perspective on the impact of companion animals in the lives of older adults and to characterize the relationship between pet ownership status and its potential relation to human health, we reframe the study of Human-Animal Interaction (HAI) in the context of social determinants of health. These broadly include neighborhood, education, and socioeconomic status, all of which may be mediated by protective factors, including social support. We also focus on a specific dimension of HAI, companion animal (pet) ownership. Pets may facilitate the formation of social connections [7] and the development of social capital [8], and many pet owners report attachment to their pets [7].
In this paper we focus on a population-based sample of Americans aged 50 and older. The human population is rapidly aging and expected to nearly double globally by the year 2050; the number of older people is expected to exceed the number of children for the first time in 2047 [9]. Most people over age 65 in the United States live independently [10], and estimates indicate that 14% of them have companion animals [11]. As individuals age, the benefits and importance of social support for the maintenance of both physical and emotional health may increase. Pet ownership may provide emotional health benefits for persons over age 65 [12] and could thus potentially facilitate successful aging.
HAI and healthy aging
Quality of life is a key element in successful aging, a term synonymous with productive and healthy aging [12]. A recent meta-analysis of research on successful aging identified four key components: 1) avoiding disability and disease, 2) having high functioning mental/cognitive/physical capacity, 3) being actively engaged, and 4) being able to psychologically adapt later in life [13]. This work suggests that social and psychological dimensions may be as important as physical and cognitive function. As a social determinant of health, human-animal interaction may be a potential element of successful aging.
A growing body of research in HAI suggests that interacting with a companion animal can offer a range of potential benefits to older adults. Interacting with a companion animal (particularly a dog) can reduce depression [14,15,16,17] or elevate mood [18], decrease anxiety [16, 19], lower blood pressure [20], and increase social interaction [21,22,23,24]. In general, researchers have less information on the impact of owning a companion animal compared to interacting with one within a therapeutic setting (such as animal-assisted therapy), due to the complex nature of these relationships and how they evolve over time. One fundamental challenge of such research is that drawing causal inferences about the impact of pet ownership on various aspects of psychological and physical health can require randomly assigning pet ownership to people. However, there are ethical and logistical concerns with this approach, and generally people prefer to determine for themselves whether or not to own a pet, and if opting for ownership, they prefer to select their own pet species.
To date, only a single study has randomly assigned pet ownership: Allen, Shykoff, and Izzo [5] conducted a clinical trial in which 48 hypertensive individuals were randomly assigned to either an experimental condition (an ACE inhibitor -Lisinopril, and pet ownership) or a control condition (only the ACE inhibitor). The ACE inhibitor was effective at reducing resting blood pressure, but failed to reduce cardiovascular responses to stress, whereas pet ownership was effective at reducing cardiovascular reactivity to mental stress. This study provides convincing evidence of the potential for pet ownership to play a causal role in mediating physiological responses to psychological stressors. In fact, in 2013 the American Heart Association summarized the results of many studies investigating the relation between pet ownership and risk of cardiovascular disease (CVD), concluding that “[p]et ownership, particularly dog ownership, may have some causal role in reducing CVD risk (Level of Evidence: B)” ([25], p. 4).
The majority of research on this topic is correlational, describing associations between pet ownership and physical and psychological health outcomes. Recent literature reviews on HAI and human aging suggest that pet ownership is positively associated with several measures of psychological and physical health in order adults (e.g., [26]), but the evidence base is small and results are often contradictory. For example, in two survival studies following myocardial infarction, one found that pet owners were more likely to die than their non-pet-owning counterparts [27]; the other found that pet-owners were less likely to die than the non-pet-owners [28].
A similarly conflicted pattern has emerged in mental health studies. McConnell and colleagues [29] reported that pet owners demonstrated higher levels of emotional well-being, self-esteem, and social inclusion, but Peacock and colleagues [30] link pet ownership to higher levels of psychopathology. Herzog [31] describes a number of potential reasons for such conflicted findings, including lack of rigorous research designs, self-report biases, the tendency to ignore non-significant findings, as well as a variety of issues related to comparing pet-owners with non-pet owners. A fundamental question that cannot be teased apart in the absence of random assignment of pet ownership status is whether obtaining a pet makes people healthier or if healthier people opt to get a pet.
Given that assigning pet ownership status is challenging in the best of scientific circumstances, our next best approach is to better understand the similarities and differences between people who self-select to be pet owners or not. Large, nationally representative studies provide this opportunity. Therefore, the purpose of this study was to explore patterns of pet ownership in a population-representative survey of older adults, and to explore the relationship between pet ownership and indicators of health and well-being.
