Photo by Janet Stephens. Public domain photo
Most health journalists have heard they should never, or at least very rarely, cover animal studies when reporting on conditions related to human health. While some opposition to reporting on animal studies includes arguments regarding the ethics of using animal models in scientific research at all, the more salient argument for most journalists is how closely or accurately the animal model can represent disease or adverse or therapeutic effects in humans.
Back in 2006, U.S. Health and Human Services Secretary Mike Leavitt noted that “nine out of 10 experimental drugs fail in clinical studies because we cannot accurately predict how they will behave in people based on laboratory and animal studies.” A study in JAMA that year similarly found that only a third of “highly cited animal research” translated to human randomized trials.
After all, humans aren’t mice, or rats, or pigs, or even monkeys. There will always be unique physiological differences between species that prevent complete translation of animal study findings to humans. And it’s important to note that even if inter-species characteristics were more similar, humans don’t live in the artificial laboratory conditions of animal models.
Key takeaway: If you’re covering an animal study, pay attention to the conditions of the lab animals’ environment and how those conditions might affect the study results.
Still, some circumstances justify reporting on animal studies, especially if there’s not another effective way to investigate a particular scientific question. One such area is environmental health research involving exposures to various chemicals. Since we can’t lock a bunch of humans away for 10 years and expose them to chemicals, animal studies can offer insights into possible physiological effects of different compounds.
Considering these studies in conjunction with observational research in humans then enables cautious conclusions about the likely effects of certain environmental exposures. This approach comprises most research about endocrine-disrupting chemicals, for example. Animal studies can also help elucidate how those effects occur, such as using research on rats to understand how diethylstilbestrol causes cancer and infertility in women prenatally exposed to it.
What to look for
But here’s the rub: It’s those very studies where an often overlooked variable can throw a monkey wrench in the works. That variable is the lab animal’s environment — its enclosure, diet, water source, the containers used to feed and water it, the room its enclosure is in, temperature and lighting, and so on.
So if you need to cover an animal study, especially if it’s related to the effects of an environmental exposure, pay close attention in the methods section to how the animals are housed, fed, watered, and cared for and whether any of those factors could influence the results. If those factors aren’t described in the study, ask the authors about it.
To illustrate, I’ll offer a few examples. An article (paywalled) by Jyoti Madhusoodanan in Nature last year examined how paying closer attention to lab animals’ diets could improve studies’ reproducibility — the lack of which is already a major hindrance in scientific research. In her opening anecdote, she describes how two different research teams produced different findings from what seemed to be the same study design — except the different teams fed the monkeys different diets.
Or, consider a study investigating the effects of a particular exposure on rats where the water bottles in the rats’ enclosures are not all identical. If some are glass and some are plastic, chemicals leached from the plastic — something that’s actually been studied in rats — could confound the results. Would any effects observed be from the chemical being studied or inadvertently from the plastic bottles?
The tale of Rat Park
Author Tara Haelle’s pet rats. Photo by Tara Haelle
My favorite example comes from a famous series of studies from the late 1970s and early 80s called Rat Park. (Although I linked the Wikipedia article there for a fast summary, this excellent comic narrating the story of Rat Park is much more entertaining.)
Before Rat Park, most research looking at animals’ self-administration of morphine involved keeping lab animals in small metal cages by themselves. But rats, like dogs, are social creatures who need enrichment, and Canadian psychologist Bruce Alexander wondered if the reason rats usually chose a water laced with morphine over plain water had more to do with their austere environment.
So he built an enclosure 200 times the size of a standard cage and filled it with every rat’s dream: food, wheels, balls and other toys, more than a dozen rat friends, and plenty of space to run, explore, and mate. It turned out, lab rats kept in this paradise had no need for morphine — even though the morphine water was sweetened — and happily sipped from the plain water bottle.
Although the experiment’s fame arose largely from how it changed the narrative of addiction — lo and behold, environment may influence the choice to self-medicate — the actual intent of the research was to understand the importance of testing conditions for lab animals. While Rat Park is an extreme example, plenty of far subtler aspects of testing conditions can affect outcomes. For example, mice and rats are nocturnal, and light during nighttime, as well as continuous light exposure and even just ambient noise, can all contribute to weight gain in rats (which, in turn, can increase the risk of multiple diseases).
The bottom line is that every little detail in a study may make a difference in the outcome. And when animal studies already have so many other obstacles to overcome in translating to humans, it’s particularly important to pay attention to those details.
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