Reprinted with permission from the online publication Zoe ( and Hal Herzog.

While writing Some We Love, Some We Hate, Some We Eat: Why It’s So Hard to Think Straight About Animals (Harper, 2011), I learned some things that really surprised me. For example, the evidence that pets enhance human health and well-being is weaker than I thought.
                I can hear the howls already. If, like me, you’re a pet lover, you’re probably convinced that your pets make you a happier and healthier person. Like most people, I thought “the pet effect” was a firmly established scientific fact.
                I’d read books like Marty Becker’s The Healing Power of Pets, and a host of newspaper and magazine articles on
the psychological benefits of pet ownership. I had also encountered many scientific journal articles that began with a statement like “The health and psychological benefits of pets on human physical and psychological health are now well-established.” And I’d heard a slew of conference presentations on “the pet effect.”
                But when I started doing the research for the pet chapter in my book, I sorted the scientific journal articles I had amassed into three stacks based on their results—the “good,” “bad,” and “ugly” piles. I was shocked by what I found.

First, the good news

A lot of studies found that health and psychological benefits do accrue from living with animals. Indeed, the field of anthrozoology (the study of human-animal relationships) was jump-started by Erika Friedmann’s groundbreaking
study showing that the one-year death rate of heart attack victims who had pets was one fourth that of people who
did not live with companion animals.
                In the three decades since Erika’s study, other benefits of pets on health and psychological well-being have been
documented. These include lower blood pressure and psychological stress, decreased doctor visits and missed days of work, better sleep, increased self-esteem, decreased loneliness and depression, healthier attachment styles, and higher levels of physical activity.

Now the bad news

But as I began to collect more articles on pets and health, I was surprised at the number of studies that found no differences in the health or happiness of people with pets and without.
                Further, this “bad” pile kept getting bigger. Among these articles were studies reporting that pet guardianship was not associated with lower psychological stress, blood pressure, heart rate, or depression. Nor was it associated with
increased happiness, life satisfaction, or exercise. And I could find no evidence that people with pets lived longer.

Finally, the really bad news

Then there was the “ugly” pile, the studies that found that pet guardians were actually worse off than people without pets (which did not even include studies of pet-induced injuries and disease). The ugly pile consisted mostly of epidemiological
studies in which pet people were found to be at greater risk for problems such as depression, anxiety, panic attacks, chronic tiredness, insomnia, obesity, hypertension, gastric ulcers, high cholesterol, and migraine headaches.
                There is, of course, no evidence that pets are the cause of these problems–just as there is little real evidence that pets cause better health. Nonetheless, one study found that pet owners had elevated diastolic blood pressure, higher body mass index, and were more likely to smoke cigarettes.
                And then there is a 2010 study of how heart attack victims fared a year after their initial coronary. After taking
demographic and basic health differences into account, the researchers discovered that the pet owners in the group were twice as likely as non-pet owners to have either died of a heart attack or to have been readmitted to the hospital for cardiac problems. Ouch!

The Bottom Line

But, you ask, if research on the “pet effect” is such a muddle of inconsistency, why do so many people believe it is
an established scientific fact?
                One reason is that we want to believe that our pets are good for us. Another is that the media loves feel-good animal stories, yet usually ignores studies that do not support the “pet effect” hypothesis. And the $50 billion-dollar-a-year
pet products industry is pushing the idea that a sweet little Yorkie can lower your blood pressure, make you lose weight, and drive away the blues.
                The bottom line, however, is that despite 30 years of research, “the pet effect” is not an established fact, but an
unsubstantiated hypothesis.

Hal Herzog is a psychologist at Western Carolina University whose research focuses on our attitudes towards and interactions with other species.