Pet ownership and risk factors for cardiovascular disease: another look

Pets can provide a range of benefits to humans, including non-judgemental companionship and the opportunity of physical contact with another living being. Researchers have also found pet ownership to be associated with health benefits, including better 1-year survival rates after acute myocardial infarction and lower blood pressure responses to psychological stress.1,2 Associations between cardiovascular health and pet ownership were explored in Australia in a 1992 cross-sectional study of 5741 community-based participants attending a free cardiovascular disease risk clinic.3 Men aged 20–60 years and women aged 40–60 years who owned a pet had significantly lower systolic blood pressure than their counterparts who did not own pets.3 While the authors of that study expressed doubts about attributing the differences to pet ownership, these findings have been widely referenced in the lay media as support for the hypothesis that pet ownership per se reduces cardiovascular risk.

Two aspects of that study indicate that these results require confirmation. Firstly, participants self-presented for free cardiovascular risk screenings. It has been noted that people who do not attend such screenings generally have a higher body mass index (BMI), higher blood pressure, smoke more often, consume unacceptably high levels of alcohol, and consider they are at higher risk of the disease.4,5 Secondly, the level of pet ownership in the Australian study was significantly lower than that found in the general population. Only 784 study participants (13.7%) owned a pet,3 while a national study undertaken two years after that study found that 60% of Australian households had pets.6 This large difference suggests that pet owners in the earlier Australian study may not be representative of pet owners in the wider community. Confirmatory analyses of associations between pet ownership and cardio-vascular disease risk factors are still required.

We used data from the PATH Through Life Project, conducted by the Centre for Mental Health Research, Canberra, Australian Capital Territory, to explore associations between pet ownership and cardiovascular risk factors.

Pet ownership was reported by 57% of participants. Compared with those who did not own pets, pet owners had less education, higher diastolic blood pressure, higher BMI, and were more likely to smoke cigarettes (Box 1). Pet owners reported undertaking more mild phys-ical exercise, while pet owners aged 40–44 also undertook more moderate physical exercise.

We then examined associations between blood pressure and pet ownership, controlling for factors that can contribute to hypertension and that were available for analysis: being overweight, being obese, hazardous or harmful levels of alcohol consumption, insufficient physical activity, and smoking (Box 2). After controlling for these factors, we found pet owners had significantly higher diastolic blood pressure than non-owners, while both groups had similar levels of systolic blood pressure.

In this cross-sectional study examining the relationship between pet ownership and cardiovascular risk factors in a random sample of 5079 participants, we found the level of pet ownership (56.96%) was comparable with that reported by a national study (60%), but significantly higher than the 13.7% reported by Anderson and colleagues.3

While Anderson and colleagues found significantly lower systolic blood pressure in men with pets and in women aged 40–60 years who had pets, we did not find such an association. Rather, we found that pet owners had similar levels of systolic blood pressure to non-owners, but significantly higher diastolic blood pressure, as well as higher BMI and a greater likelihood of being smokers.

After controlling for other hypertensive factors, we found that pet ownership per se provided no cardiovascular gain by reducing blood pressure. Instead, pet owners again had significantly higher diastolic blood pressure. The health risks implied by this finding must be qualified with the caveats that current research identifies systolic blood pressure as being more important, and that blood pressure is only one of a number of cardiovascular risk factors.8 Nonetheless, our study does not support the earlier finding that pet ownership provides cardiovascular benefit as assessed by blood pressure.

The cross-sectional study of Anderson and colleagues has been the only report in the peer-reviewed literature that indicated an association between pet ownership and cardiovascular health benefit outside experimental research settings. Consequently, its findings have carried considerable weight in the broader community. We have no doubts that carefully selected and cared for pets can provide many emotional benefits for humans. Many pet owners would consider such benefits to easily justify the time and energy spent on their non-human companions. However, longitudinally based research on pet ownership and health needs to be conducted before specific cardiovascular health gains can be attributed to owning pets.