Living with animals is good for our health. Lovely thought, but Hal Herzog says we’re too keen to believe it
WHY is it so difficult to think straight about animals? How do we assess the comparative cruelty of cockfights and Happy Meals? Is it really OK to use millions of mice in the hunt for a cure for baldness? And what makes us think the things we think about animals that don’t think like us?
These are questions I pose in my new book, Some We Love, Some We Hate, Some We Eat, and they are questions I hope the new science of anthrozoology will address in the coming years as it draws together psychologists, vets, sociologists, ethologists, anthropologists and others to study the complexities of human interactions with other species.
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One of the field’s current controversies – over whether interacting with animals alleviates human suffering – ties together some of my questions. There are reports of all sorts, from reasonable claims that stroking a cat lowers blood pressure to over-the-top ones such as swimming with dolphins alleviates autism and shrinks tumours. Sorting out the genuine science is going to be interesting.
I made a small start when I decided to check the research underpinning an article in my local newspaper, which claimed regular visits by “therapy dogs” improved the psychological adjustments of cancer patients. The original research turned out to be a clinical trial at the University of Missouri in which people undergoing radiation therapy were randomly placed in either a dog-visitation group, a human-visitation group, or a quiet reading group. The study was well-designed and the results clear and surprising: the data actually indicated that the dog visits had no effect on the health or happiness of the patients.
Public fascination with the healing powers of pets was fuelled by a study in 1980 of people who survived heart attacks. A research team lead by Erika Friedman, now at the University of Maryland in College Park, studied 92 people and found that 6 per cent of the pet owners in the study died within 12 months compared with 28 per cent of non-pet owners.
There have now been hundreds of studies on the medical and psychological impacts of interacting with animals, ranging from the cardiovascular benefits of petting a boa constrictor to horse riding as a treatment for attention-deficit hyperactivity disorder. From them emerges what looks like reasonably good evidence that beneficial effects sometimes accrue from living with animals. For example, several studies have found children brought up with pets are less susceptible to asthma, while a study of Germans and Australians reported pet owners made fewer visits to the doctor. Chinese women who owned dogs were found to sleep more soundly, take fewer sick days and feel better than dog-free women.
But what never seem to make the headlines are the many studies which showed pets to have no effects, or even adverse effects, on their owners’ health and happiness. For instance, Deborah Wells at Queen’s University Belfast, UK, reported that pet-owners with chronic fatigue syndrome were convinced that their companion animals provided them with a host of psychological and physical benefits, but objective measures showed they were just as tired, depressed, worried and unhappy as CFS sufferers without animals.
Epidemiologists in Finland found that pet ownership was associated with high blood pressure, kidney disease, arthritis, sciatica, migraines, panic disorders and obesity. Researchers at the Australian National University in Canberra reported that adults aged 60-plus who lived with pets were more likely to be depressed, take pain medication and generally be in worse mental and physical shape than pet-free people. And a recent study from the University of Western Australia in Perth found that while acquiring a dog increased the frequency of recreational walking by their owners, the total amount of exercise they got each week did not change.
After reading many studies of the effects of pets on people, I have tentatively concluded that, on the whole, pets are probably a healthy pleasure, though not to the degree that the pet industry would have us believe. The challenge for researchers is to figure out to what extent interacting with animals can benefit human health and why. The extent question is made difficult by the fact that negative results are seldom published – the “file-drawer effect”.
At last year’s meeting of the International Society of Anthrozoology I attended a session which illustrated this phenomenon. Presentations of three studies on the effects of animals on psychological well-being in groups such as college students and people living in nursing homes all clearly showed that pets had no effect, yet researchers told me they did not plan to submit their results to a journal.
A 2008 study published in The New England Journal of Medicine on the effectiveness of 12 anti-depressant drugs illustrates how ignoring unpublished studies can skew scientific findings (). The researchers found that overall, the studies that the US Food and Drug Administration judged to show positive results were about 12 times as likely to be published as studies with non-positive results. When the data from the unpublished research were included in the analysis, the estimates of the average effectiveness of anti-depressants dropped by 32 per cent. I suspect a similar decline would be true of animal therapy studies.
Replication is also a problem with research into human-animal relationships. A decade ago, researchers in Pretoria, South Africa, reported that levels of oxytocin (dubbed the “love hormone”) increased when people pet dogs. Even though there were only 18 subjects, the study has been widely used as proof that the hormone is the chemical glue that cements the bonds between people and pets. Three research groups have tried to replicate the original study. One found the effect only in women, another only among people who gazed at their dogs, and the third found that petting dogs had no influence on oxytocin levels. (This last study was not published.)
Some research on the benefits of living with animals is just plain bad science. For a meta-analysis of the effectiveness of animal-assisted therapy, Brad Lundahl and his team at the University of Utah in Salt Lake City combed through 250 studies and could only find 39 that included data that met even minimal standards of rigour. And researchers Lori Marino and Scott Lilienfeld of Emery University in Atlanta, Georgia, concluded that nearly every study purporting to document the benefits of therapy based on swimming with dolphins is methodologically flawed.
Finally, because most studies on the benefits of living with companion animals on our mental and physical health are based on comparisons of people who own pets with those who do not, we know little about why pet-keeping may be associated with better health. Which way, for instance, does the causal arrow point? Does living with an animal make us healthier and happier, or are individuals who are healthy and happy to begin with more likely to acquire pets?
“People who are healthy and happy to begin with may be more likely to acquire pets”
Hopefully, we will have better answers quite soon. Human-animal interaction research centres are popping up all over the world, and the holds annual conferences and publishes a peer-reviewed journal, ´ˇ˛ÔłŮłó°ů´Çłú´Çö˛ő. For now, I’d say be careful about uncritically accepting claims about the miraculous healing powers of pets – and don’t forget to walk the dog!
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Hal Herzog is professor of psychology at Western Carolina University, North Carolina. This article was developed from his book, Some We Love, Some We Hate, Some We Eat: Why it’s so hard to think straight about animals, published by HarperCollins (2010)
