As dogs age, many develop more than one chronic health condition. New research from the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) shows those conditions can dramatically shorten a dog's lifespan, highlighting the importance of managing multiple diseases together rather than individually.
In a recent study published in GeroScience, researchers with the Dog Aging Project found that dogs with five or more chronic diseases were more than twice as likely to die as dogs living with only one diagnosed condition, regardless of their age or size. The findings suggest that, as in humans, chronic diseases interact in ways that make their combined effects more harmful than each condition alone.
"Multimorbidity refers to the fact that individuals often become ill with more than one chronic disease at the same time," said Dr. Kate Creevy , chief veterinary officer for the Dog Aging Project and a professor in the VMBS' Department of Small Animal Clinical Sciences . "We know in people that being sick with more than one thing is frequently more damaging to health and survival than simply adding up the effects of two different diseases. We wanted to understand if the same thing is true for dogs."
Rather than simply identifying which diseases are most common, the researchers hope the work will eventually help veterinarians decide where to focus treatment when pets are living with multiple chronic conditions.
Many owners face difficult decisions about medications, specialist visits and treatment costs as their pets age. Understanding which diseases have the greatest influence on long-term health could help veterinarians focus care where it matters most.
"If we can identify which conditions are most likely to cause harm or contribute to other problems, we can help owners prioritize their healthcare investment, the time they spend, the money they spend and the challenges of managing multiple therapies," Creevy said. "This is really just the first step in that research pathway."
Tracking more than 50,000 dogs
For the study, researchers analyzed health information from more than 50,000 dogs enrolled in the Dog Aging Project; participating owners report any medical diagnoses their dogs have received each year, allowing researchers to follow changes in health over time.
The team compared the health histories of dogs that had died with those that were still living, accounting for differences in age at enrollment and the length of time each dog had participated in the project.
The analysis confirmed that dogs, like humans, accumulate more chronic conditions as they age and that those conditions can become intertwined. For example, a dog with osteoarthritis may become less active and gain excess weight, while excess weight can also increase a dog's risk of developing osteoarthritis.
More importantly, the study showed that the number of diseases a dog develops has a substantial impact on survival, even after accounting for factors such as age and size.
"We are all eventually going to die, but this analysis asked the question: for any given year of life, how likely is the dog to die this year?" Creevy said. "Dogs with five or more conditions were more than twice as likely to die than dogs with a single condition reported. It shows that the magnitude of this impact is pretty dramatic."
Some conditions matter more than others
Beyond counting diseases, the researchers also examined which health conditions tended to occur together and which conditions were most strongly associated with shorter lifespans.
Among the disease combinations linked to shorter lifespans, cancer and osteoarthritis emerged as one of the most common and concerning. Dogs with significant dental disease also frequently had other chronic illnesses, while hearing loss appeared regularly among dogs living with multiple conditions.
Rather than acting independently, many of these diseases appear to reinforce one another.
"Cancer can affect multiple body systems as it spreads," Creevy said. "Similarly, osteoarthritis can interfere with the activities of daily living. If a dog can't move comfortably, it may exercise less, drink less water or have difficulty getting outside, and those consequences can lead to additional health problems."
Excess weight also played an important role because it can both contribute to chronic disease and result from it. This two-way relationship illustrates how diseases can become interconnected, potentially compounding their effects on a dog's overall health.
Lessons for dogs — and people
The study also reinforces the growing value of companion dogs as models for understanding healthy aging in people.
Because most dogs live 10 to 12 years, researchers can study an entire lifespan in little more than a decade. Answering similar questions in humans can require following participants for 70 years or longer.
As scientists continue studying how chronic diseases interact, discoveries made through dogs may eventually guide healthcare strategies for both species.
For now, Creevy says many of the same recommendations veterinarians have made for years remain some of the most effective ways owners can support healthy aging.
Keeping pets at a healthy weight, encouraging regular physical activity, and maintaining good dental health may all help reduce the burden of chronic disease as dogs grow older.
Creevy credits the thousands of owners who volunteer their pets' health information through the Dog Aging Project for making studies like this possible.
"The reason we can learn this is because so many dedicated volunteer owners have shared their data with the Dog Aging Project," Creevy said. "Their willingness to tell us what happens to their dogs over several years is what makes this kind of research possible."
By Camryn Haines, Texas A&M University College of Veterinary Medicine and Biomedical Sciences
