For more than a decade, in blog posts and scientific papers and public talks, the psychologist Hal Herzog has questioned whether owning pets makes people happier and healthier.

It is a lonely quest, convincing people that puppies and kittens may not actually be terrific for their physical and mental health. “When I talk to people about this,” Herzog recently said, “nobody believes me.” A prominent professor at a major public university once described him as “a super curmudgeon” who is, in effect, “trying to prove that apple pie causes cancer.”

As a teenager in New Jersey in the 1960s, Herzog kept dogs and cats, as well as an iguana, a duck, and a boa constrictor named Boa. Now a professor emeritus at Western Carolina University, he insists he’s not out to smear anyone’s furry friends. In a blog post questioning the so-called pet effect, in 2012, Herzog included a photo of his cat, Tilly. “She makes my life better,” he wrote. “Please Don’t Blame The Messenger!”

Plenty of people believe there’s something salubrious about caring for a pet, similar to eating veggies or exercising regularly. But, Herzog argues, the scientific evidence that pets can consistently make people healthier is, at best, inconclusive — and, at worst, has been used to mislead the American public.

Few, if any, experts say Herzog is exactly wrong — at least about the science. Over the past 30 or so years, researchers have published hundreds of studies exploring a link between pet ownership and a range of hypothesized benefits, including improved heart health, longer lifespans, and lower rates of anxiety and depression.

The results have been mixed. Studies often fail to find any robust link between pets and human well-being; some even find evidence of harms. In many cases, the studies simply can’t determine whether pets cause the observed effect or are simply correlated with it.

Where Herzog and some other experts have concerns is with the way those mixed results have been packaged and sold to the public. Tied up in that critique are pointed questions about the role of industry money on the development of a small field — a trend that happens across scientific endeavors, particularly those that don’t garner much attention from federal agencies, philanthropies, and other funding sources.

The scientific evidence that pets can consistently make people healthier is, at best, inconclusive — and, at worst, has been used to mislead the American public, Herzog argues.

The pet care industry has invested millions of dollars in human-animal interaction research, mostly since the late 2000s. Feel-good findings have been trumpeted by industry press releases and, in turn, dominated news coverage, with headlines like “How Dogs Help Us Lead Longer, Healthier Lives.”

At times, industry figures have even framed pet ownership as a kind of public health intervention. “Everybody should quit smoking. Everybody should go to the gym. Everybody should eat more fruits and vegetables. And everyone should own a pet,” said Steven Feldman, president of the industry-funded Human Animal Bond Research Institute, in a 2015 podcast interview.

The problem with that kind of argument, Herzog and other experts say, is that it gets out ahead of the evidence (and that not every person is equipped to care for a pet). “Most studies,” said Herzog, “do not show the pattern of results that the pet products industry claims.”

It seems safe to say that most people don’t get a dog in order to marginally lower their odds of developing heart disease. Pet effect research falls into a strange family of science that measures the practical health outcomes of things people typically do for decidedly non-practical-health-related reasons, like get married or have children.

At the same time, there’s evidence — much of it anecdotal — that at least some people are cognizant of the potential health benefits when choosing to get a pet. And the idea makes intuitive sense to many people, who say their animals are good for their well-being. Concurrently, hospitals and nonprofits have rolled out programs that aim to use therapy dogs and support animals to improve people’s mental health.

James Serpell began studying the pet effect in the early 1980s, as a young animal behavior researcher. At the time, spending on pets was rising in the United States; people were beginning to treat pets more like family members. But there was little research on people’s relationships with their animals. “Why are we doing this?” Serpell wondered. “What’s it all about?”

In an influential 1991 paper comparing non-pet-owners with people who had recently adopted an animal, he supplied some of the first published data suggesting that new pet owners experienced a measurable reduction in minor health problems. New dog owners also pursued more physical activity, compared to people who had cats or no pets at all.

In the decades since, researchers have published dozens of studies comparing pet owners to non-pet-owners. The results are mixed — sometimes pointing toward health benefits, and sometimes not.

Some of that data may reflect the realities of human-animal relationships — which, like any other kind of relationship, can vary for all sorts of reasons. “It doesn’t mean that my lived experience or anyone else’s lived experience is wrong,” said Megan Mueller, a human-animal interaction expert at Tufts University. “What it means is that it’s different for different people.”

For some people, she said, having a pet can bring stressors. The caretaking responsibilities may be too taxing; the pet may exacerbate family tensions or trigger allergies; the owner may be unable to afford pet food or veterinary care.

The results, some experts say, are also muddied by longstanding issues with research methods. The problem is that there are differences between the people who choose to own pets and the people who don’t.

“What happens is we try to compare people with pets, to people without pets, and then we say, ‘People with pets have X, Y, and Z differences.’ It actually is a really invalid way of approaching the research question,” said Kerri Rodriguez, who directs the Human-Animal Bond Lab at the University of Arizona. A study finding that cat owners are more likely to be depressed, for example, may be picking up on a real connection. But it could just be that people already experiencing depression are likelier to get cats.

Some of the data may reflect the realities of human-animal relationships — which, like any other kind of relationship, can vary for all sorts of reasons.

Today, Rodriguez mostly studies service animals, especially for veterans at risk for PTSD. In this context, it’s possible to conduct randomized trials — for example, randomly choosing who will get a support animal now, and who will go onto a waitlist to get a companion animal later. Some research on service dogs — including a recent controlled, but not randomized, trial that Rodriguez was involved with — has shown clear benefits.

How much those benefits apply to typical pet owners, experts say, is unclear. And it’s hampered by the inability to conduct those kinds of randomized trials. (“You can’t randomize people to pet ownership,” said Rodriguez.)

Rodriguez said she’s interested in studies that track the association between human-pet relationships and health metrics over time, checking in with people again and again and collecting larger amounts of data. One such study, for example, found a slower rate of executive decline among older pet owners.

Serpell, after his 1991 study, largely moved on to other research questions. “I basically concluded that this type of research was too difficult,” he said. “And even if you did it, the results you would get would always be questionable.”

Those doubts have not deterred interest in the field from the companies that lead the pet industry, which is today valued globally at more than $300 billion.

Almost from the start, the quest to understand the pet effect has been entangled with industry money. Serpell’s earliest work was funded by what is now known as the Waltham Petcare Science Institute, a division of Mars, Inc., which owns a portfolio of pet food and veterinary care brands in addition to its famous candy business. “There was no other source of funding, really,” recalled Serpell, who’s now an emeritus professor at the University of Pennsylvania. “Nobody else was willing to put money into this field.”

In 2008, Mars entered a partnership with the National Institutes of Health in order to spur more research into animal-human interactions. In the first year, the pet product provider ponied up $250,000, while the federal government supplied $1.75 million. (The NIH partnership ended in 2022, although Mars continues to underwrite research on pets and human health.)

Almost from the start, the quest to understand the pet effect has been entangled with industry money.

In 2010, a group of pet industry heavyweights launched the Human Animal Bond Research Institute, or HABRI. Key funders have included Petco, Purina, and Zoetis, a veterinary pharmaceuticals firm. “Pets and animals make the world a better place, and we’re going to use science to prove it,” said founding director Steven Feldman in a 2014 talk at a conference for pet bloggers.

The nonprofit has spent more than $3 million funding research on human-animal interactions. Companies also directly fund university research: One prominent research lab at the University of Arizona — separate from Rodriguez’s research group — includes a sponsor page on its website featuring the logos of Nestle Purina, Mars Pet Care, veterinary drugmaker Elanco, and other pet product companies.

“Funding from the pet industry has transformed the field, and without it, we would not have the science that we have,” said Mueller. (Like Serpell and Rodriguez, Mueller has received industry funding for some of her research.)

Did that funding shape the field’s findings? “I think it has largely been done in a really ethical way,” said Mueller. She and Rodriguez both said they had never felt pressure to produce a particular result. Waltham, when it entered the partnership with NIH, gave up the right to select who would get the funding. Industry-funded studies have found — and published — results suggesting little benefit from pets.

“I really think that field has done a good job of publishing a lot of findings that are maybe not what people would expect,” said Mueller.

Herzog said he has seen little evidence that industry money has changed the science. Mostly, he said, “they’ve funded pretty good studies.” But there are ways it can change the field. “It’s always been a source of great ambivalence, I think, for everybody involved,” said Serpell. “You try and work around it, by getting whoever funds the work to stay off your back and let you do the work, and if they don’t like the results, that probably means the next time you apply to them for funding, you won’t get it.”

The funding can shape the questions that the field asks — or avoids. “Industry-funded studies tend to produce results that favor the sponsor’s interest,” said Marion Nestle, an emeritus professor at New York University who has spent decades studying corporate influence on science. Sponsors influence what gets studied, Nestle said, and they select for studies that they think will produce positive results. And, she said, research suggests sponsorship can shape the way results are interpreted — often without researchers being aware of the influence at all.

Controlling the focus of the research can also steer scientists away from certain topics entirely. “For obvious reason, these companies don’t wish to draw attention to the darker side of the human-pet relationship,” said Serpell, referring to research areas such as dog bites.

In a recent Zoom interview, Feldman, the HABRI president, said funders “can tell us what kind of things they’re hoping to see,” and the organization will try to accommodate those requests. “But then, once the process of funding a project begins, there’s absolutely no influence there whatsoever.”

Research suggests that sponsorship can shape the way results are interpreted — often without researchers being aware of the influence at all.

HABRI embraces negative results, or those that don’t show a clear effect from pet ownership, and not just positive findings, Feldman said. But, he acknowledged, they may choose to emphasize positive results. “We try and be very true to the science, but if we take a slightly more optimistic view as to the body of work than researchers who take a different perspective, I think that helps generate a lot of positive behavior in the real world.”

Herzog, Feldman suggested, was making a name for himself with naysaying — in ways that, perhaps, sometimes defy common sense. A 2021 HABRI survey found that nearly 9 in 10 pet owners report that their pets benefit their mental health. “I kind of think pet owners might be on to something,” Feldman said.

Herzog agrees that having a pet can have real benefits. At the end of a recent conversation, he reflected on his cat, Tilly, who died in 2022. She used to watch TV with him in the evenings, and she would curl up on a rocking chair in his basement office while he worked. The benefits of their relationship, Herzog said, were real but perhaps hard to measure — among the intangible qualities that are difficult to capture on research surveys.

“If you’d asked me, ‘Did Tilly improve the quality of your life?’ I’d say absolutely,” he said. “My health? Nah.”

This article was originally published on Undark. Read the original article.