Animal aging is a modifiable risk factor. Here is what veterinarians can do about it

For most of veterinary medicine's history, aging has been accepted as a fact of life rather than a target for intervention. Brennen McKenzie, VMD, MSc, MA, thinks that framing is both outdated and costly to patients. As director of veterinary medicine at Loyal, a biotechnology company working to extend the healthy lifespan of dogs, McKenzie argues that aging is a modifiable risk factor and that addressing it doesn't require waiting for the next breakthrough. In this Q&A, he breaks down what the science of aging means for everyday clinical practice, from managing body weight and metabolic dysfunction to emerging therapies targeting the biology of aging itself.

Editor’s note: This dvm360 Q&A has been edited and consolidated from a verbal interview to better fit a written format while retaining the substance of the original conversation.

dvm360: To start, can you introduce yourself to our audience?

McKenzie: I'm Brennen McKenzie. I'm a small-animal veterinarian, currently split between part-time private practice—where I've been for almost 25 years—and my role as director of veterinary medicine for Loyal, a biotechnology company based in San Francisco, [California]. Our mission is [to develop] medications to extend the healthy lifespan of dogs.

dvm360: What are the key biological mechanisms that drive aging and age-related disease in dogs?

McKenzie: There are many mechanisms, and a lot of them have been organized under a framework called the “hallmarks of aging,” which is widely used to categorize the complicated biology of aging in a way that makes it easier to investigate and identify new therapies. One that we're particularly interested in at Loyal is metabolic dysfunction. As people and dogs get older, our energy metabolism becomes less efficient. We all know [what that’s like]. I used to be able to eat whatever I wanted, and I never gained weight, and I felt great. Now at my age, I can't do that anymore. So that involves internal changes—things like reduced insulin sensitivity, which causes insulin levels to rise and can drive risk for cancer or dementia, and changes in blood lipids. In humans, elevated cholesterol tends to lead to heart attacks and strokes. It doesn't cause that in dogs, but it causes other kinds of health problems in a similar way. Metabolic dysfunction is an area of particular interest for us because it's something we've seen success in treating in a variety of ways.

dvm360: How does viewing aging as a modifiable risk factor change the way veterinarians can approach preventive care?

McKenzie: We've always thought of aging as this inevitable, immutable fact of the universe—something we can't do anything about and just have to cope with. That may have been true at one point, but we now know enough about the biology of aging [and] have useful tools to slow the process and maintain health, function, and quality of life for longer. It makes me sad when a client comes in and says their pet is slowing down because they're getting old, but that's OK. That's usually not true. Usually, there's a problem: They may not be comfortable, they may have arthritis or pain, or they may be carrying too much weight—all things that can potentially be treated, but we write them off as just aging. Thinking of aging as a modifiable risk factor for what I call the 3 Ds—disability, disease, and death—makes us as veterinarians more proactive and more likely to intervene earlier, before we see obvious disease and a significant decline in quality of life.

dvm360: What can veterinarians do right now to help delay disease onset and potentially extend a dog's lifespan?

McKenzie: For now, the available tools aren't super high-tech, but they're still very impactful. One of the most important is helping clients maintain a healthy body weight in their pets. Obesity and being overweight are significant drivers of metabolic dysfunction, and they compound the dysfunction that comes with aging. The scientific literature is very clear that keeping animals at a healthy, lean body weight means they'll feel better, have less disease, and live longer. Beyond that, routine preventive care matters more than people might think. Pets whose owners bring them in regularly for vaccinations, stay consistent with parasite prevention, and do appropriate screening blood work are healthier and live longer. Those are the tools vets have right now, and they're meaningful ones.

dvm360: When it comes to nutrition, what aspects matter most for supporting healthy aging in dogs?

McKenzie: Nutrition is complicated. There are a lot of diets marketed for senior pets, but we don't actually have an official [Association of American Feed Control Officials] senior diet category, because the reality is we don't know exactly what optimal nutrition looks like for aging dogs or cats in general—and it's likely that there isn't one universal answer. Each individual is going to need a unique set of nutritional inputs to maximize health and well-being. The most important thing right now is not overfeeding—maintaining a healthy, lean body weight is key. There's some encouraging information suggesting that higher-protein diets may be beneficial, and some interesting but not yet conclusive data on fresh, cooked diets. But there's still a lot of uncertainty. The one thing I can say with confidence is that most cases of age-related disease will likely benefit from essential fatty acid supplementation.

dvm360: What emerging therapies show promise for supporting healthy aging in dogs?

McKenzie: At Loyal, we're working on a couple of programs. One focuses on large-breed dogs. We know that the larger a dog is, the shorter their lifespan [is], and that's a consequence of intensive breeding for body size, which has produced a chronic overexpression of growth-related hormones. Some of these very large-breed dogs essentially have a growth disorder—a kind of acromegaly—and that accelerates the pace of aging significantly. We're developing medications to lower insulin-like growth factor 1, one of those growth hormones. If we can bring those levels down after a dog is fully grown—closer to what you'd see in a small- or medium-sized dog—we may be able to slow that abnormally accelerated aging. The other program targets metabolic dysfunction directly. We know from caloric restriction studies that improving insulin sensitivity and other aspects of metabolic function is very effective at delaying age-related disease and extending healthy lifespan, but caloric restriction is hard to execute safely and consistently. Medications that mimic some of those same effects may offer a safer and more practical path to the same benefits.

dvm360: What are your key takeaways on aging as a modifiable risk factor in dogs?

McKenzie: Three things. First, aging is not a mystery. It's complicated, but it's comprehensible, and we understand the biology well enough to do something about it. Aging is a modifiable risk factor for disease, and we can modify it to help our patients live healthier, longer lives. Second, the way to do that right now is straightforward: Keep patients at a healthy body weight and engage in good-quality preventive care. Third, communicate with your clients. They want the best for their pets, the same as you want the best for your patients. Keep those channels open and work together as a team.