companion animals Companion or pet animals are an integral part of many societies. Over the last two decades a body of literature has accumulated highlighting the potential benefits which these animals may bestow on our health.

Pioneering work in this area was conducted by Erika Friedmann and co-workers in the US in 1980. Initially they were interested in the effects of social relationships and personality on the survival of people who had suffered heart attacks, and they included questions about pet ownership. Follow up, one year later, showed that certain aspects of social support, or a lack of it, were found to be important predictors of one-year survival. Unexpectedly, they found that pet owners had a greater chance of being alive one year after a heart attack than non pet owners. This apparent effect of pet ownership was not due to the extra physical exercise which dog owners engaged in, since other kinds of pet owner also seemed to benefit. There were also no pre-existing differences between the personalities of pet owners and non pet owners. The study generated much interest, and led to new studies on the potential health benefits of pet ownership and the mechanisms for these effects. Friedmann also worked on a follow-up study in the 1990s using a much larger number of patients, and again found that pet ownership, and dog ownership in particular, promoted cardiovascular health, independently of social support and the physiological severity of the disease.

A large epidemiological study in Australia provided some evidence that pet ownership may actually reduce the risk factors for developing coronary heart disease. Warrick Anderson, in the early 1990s, examined standard cardiovascular risk factors among 5741 people attending a screening clinic at the Baker Medical Research Institute in Melbourne, Australia. A comparison of pet owners and non pet owners revealed that pet owners had lower systolic blood pressures and blood fat levels (plasma triglycerides) than the non pet owners. When men and women were compared separately, male pet owners had significantly lower systolic blood pressure, cholesterol, and plasma triglyceride levels than non owners. Interestingly, pet owners did not behave in a consistently more healthy manner than non pet owners. They were more physically active and yet they were also more likely to be drinkers, to eat take-away meals, and to consume meat more than 7 times per week. Women over 40 years of age were more likely to have lower systolic blood pressures if they were pet owners than if they were not. Although one could again speculate that dog owners would show the most benefit compared with other pet owners because of having to exercise the animal, in fact no differences could be detected between these two groups in relation to blood pressure, cholesterol, or triglyceride levels.

Apart from there being an interest in the effects pets can have directly on physiological parameters related to coronary heart disease, there has also been interest in the effects these animals have on our general health. James Serpell interviewed 71 adults in Cambridgeshire, UK shortly before they were to acquire a new cat or dog, and then followed them up at 1 and 10 months after acquisition. For comparison purposes, a group of people were included who did not acquire a new pet during the course of the study. In addition to obtaining basic personal and sociodemographic details, the questionnaires filled in by the participants included three self-report measures of physical and psychological health. Not surprisingly, dog owners increased the amount of daily exercise they engaged in. Both cat and dog owners reported significantly fewer minor health problems (e.g. colds, flu, hay fever, indigestion) and fewer emotional concerns during the first month of ownership compared with those who had not acquired a new pet. Only dog owners, however, maintained this over the full 10 months of the study. As with the studies mentioned previously, these benefits for dog owners could not be explained by the increased exercise levels.

A more recent, similar study by Elizabeth Paul and James Serpell in Cambridgeshire considered the effects of new pet dog acquisition on the lives of children and their families. However, unlike the positive effects found in previous studies with adults, dog-owning children were reported to have experienced significant increases in the number of ill health symptoms (e.g. colds, flus, headaches, ear ache, asthma) they suffered in the 12 months after obtaining a new dog. The researchers concluded that possibly for children, if not for adults, a variety of minor zoonoses and/or allergies may be significant consequences of keeping a dog, at least during the first 12 months or so of ownership.

Much interest has also centred on the potential short-term anti-anxiety effects companion animals may have on people. In the early 1980s, Aaron Katcher in the US measured the blood pressures of pet owners while they rested without their pets, interacted with (touched, talked to) their pets, and read aloud in the same room without their pets. The blood pressures rose significantly while reading aloud (this is a common response), however, talking to and handling the pets did not cause an increase in blood pressure.

At about the same time, Erika Friedmann and co-workers in the US studied the effects of an animal's presence only (no contact) on cardiovascular changes occurring during speech. Here they measured children's blood pressures and heart rates while they rested silently and while they read aloud, both with and without an unfamiliar but friendly dog in their presence. The presence of the friendly dogs was found to lessen the blood pressure response to reading aloud.

Mara Baun and co-workers, again in the US, studied the effects of petting one's own dog without talking to it, compared with the effects of petting an unfamiliar dog and with the effects of reading silently. Blood pressures decreased significantly over the assessment period for owners petting their own dogs, but not for those with unfamiliar dogs. These changes in blood pressure paralleled the relaxation effect of quiet reading.

Although interacting with friendly, unfamiliar dogs may not be as good for you as interacting with your own dog, Cindy Wilson in the US showed that they still can reduce the physiological and psychological consequences of stress for dog owners and non owners. She monitored the blood pressures and heart rates of students during three activities: reading aloud, reading quietly, and interacting with (talking to, petting) a friendly but unfamiliar dog. Anxiety was also measured, using a special questionnaire which the person filled out between each activity. All parameters measured (heart rate, blood pressure, anxiety) were found to be significantly higher during the reading aloud period than during the pet interaction period.

While the majority of the research in this area has involved dogs, this does not mean that other animals cannot have the same effects on people. Indeed, watching fish in an aquarium can lead to decreases in both blood pressure and anxiety. Aaron Katcher and co-workers in 1983 found that the blood pressures of normal patients and of those with hypertension decreased significantly while watching fish swim in an aquarium. These reductions were similar to those reported for relaxation therapy or transcendental meditation. Katcher also found that, for dental patients, watching fish swim in an aquarium before dental surgery proved to be an effective means of increasing patient compliance and of decreasing perception of pain during the dental procedure. Additionally, the effect of watching fish was determined to be equivalent to the effect of hypnosis.

However, it is important to note that not all studies have found a positive effect of companion animals on physiological responses to stress. For example, in the late 1980s, John Grossberg and co-workers found that neither blood pressure nor heart rate responses during mental arithmetic and psychological assessment were different for college students accompanied by their own dogs during the experiment than for the dog owners who were unaccompanied.

The ability of companion animals to positively affect our lives is therefore somewhat variable, and this is because there are numerous factors which may influence the way in which we respond to the presence of animals and to touching or talking to them. The type of stress (mental arithmetic, sound of a doorbell, telephone ring), the quality of the human support we have, our personality and relationship with the animal, and the behaviour of the animal can all play a part. Further research is required to determine just what it is about the human–companion animal relationship that can help us both physically and mentally, and under which circumstances.

A. L. Podberscek

Bibliography

Wilson, C. C., and Turner, D. C. (ed.) (1988). Companion animals in human health. SAGE, London.