Pets can be good for you – but the evidence shows it’s not quite that simple

When it comes to pet ownership, emotions often run high. Those who share their lives with a pet can be passionate about the benefits they feel their animal companion brings. However, the scientific evidence is variable, with some studies showing physical and mental health benefits in humans who spend time with pets, and others showing little or no benefit or even negative effects.

A common problem in studies of pet ownership and human health is that they usually study people who have already chosen to welcome a pet into their family. This is understandable, as there are obvious ethical issues with a study that randomly assigns pets to potentially unwilling participants. As a result, studies may fail to take proper account of other factors that are associated with improved health, such as gender, age, race/ethnicity, living arrangements, and income. Could it be that certain people, who are already likely to enjoy a better standard of health, are also more likely to own a pet?

Recently published results of a large scale survey were able to go some way towards answering this question. The study was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health-Mars/WALTHAM public private partnership and published in the journal PLOS One. Over 42,000 people living in California were quizzed about their health, lifestyles and whether or not they owned any pets. 26.2% of respondents owned a dog, 21.5% owned a cat, and 8.5% owned both a dog and cat.

Spot the difference

Pet owners differed from non-pet owners across many socio-demographic variables. Moreover, many of these are known to influence health and other outcomes. Overall, the survey showed that pet owners are more likely to be single females or married people, younger, white, live in more rural areas, and belong to households where everyone is employed full time. Additionally, dog owners are more likely to be home owners and generally have a higher household income.

These differences are far from trivial. They suggest that some of the health differences observed between pet owners and non-owners could be due to differences in age, race, gender, employment, income, and housing. Pet ownership may be irrelevant.

“Our study shows that pet owners differ from non pet owners in important ways that relate to overall physical and mental health" said lead author Dr. Jessica Saunders of the RAND Corporation. "The motivation behind the decision to cohabitate with a pet may also be an important determinant about how this relationship may be associated with health" she added "For example, some people may want companionship and emotional support whereas others may be looking for an exercise buddy”

Selection bias

The paper acknowledges the challenge of overcoming this so-called “selection bias” when drawing conclusions about the impact of pet ownership on human health and makes suggestions for how future studies can address it.