Brennen McKenzie, MA, MSc, VMD

Age-related diseases have long been thought of as inevitable, natural consequences of getting older. The traditional medical response to age related diseases such as cancer has been to detect and treat them as early as possible, to cure if possible and reduce suffering and prolong life when an illness cannot be cured. These are important and valuable approaches but in an ideal world, the best approach is always prevention.

Preventative veterinary medicine has been incredibly effective at reducing the burden of infectious disease, parasitism, malnutrition, injuries, and many other causes of suffering and death in dogs. However, the options are limited for preventing the many diseases of aging. Maintaining a healthy body weight, regular exercise, and a few other lifestyle interventions do reduce risks to some extent, but we need to turn our growing understanding of the mechanisms of aging into therapies that address aging itself.

The direct way to accomplish this is through interventions that prevent or delay the occurrence of specific age-associated diseases. If targeting particular mechanisms of aging can reduce the chances of our dogs developing cancer, for example, this would prolong life and preserve health for many individuals because cancer is a leading cause of death in aged dogs. 

However, the immediate cause of death for most dogs is not any specific disease but rather euthanasia. We choose to let our dogs go when it is clear that they are experiencing significant suffering or loss in quality of life. 

Aging also leads to a general loss of comfort, function, and resilience, a condition known as frailty. One of the greatest potential benefits of targeting the underlying mechanisms of aging would be to slow the onset of frailty. Keeping dogs biologically younger for longer evwould extend healthspan and could also indirectly lengthen life by delaying the point at which quality of life has declined so much that euthanasia is necessary. 

Immortality, of course, seems unlikely for complex biological organisms, and fatal illness or unacceptable frailty is likely inevitable for all dogs eventually. However, there is great potential to improve overall quality of life by compressing the period of significant disease and disability to as small a fraction of the lifecycle as possible and extend those prime, healthy years. 

Is aging inevitable?

Age-related diseases have long been thought of as inevitable, natural consequences of getting older. The traditional medical response to age related diseases such as cancer has been to detect and treat them as early as possible, to cure if possible and reduce suffering and prolong life when an illness cannot be cured. These are important and valuable approaches but in an ideal world, the best approach is always prevention.



Preventative veterinary medicine has been incredibly effective at reducing the burden of infectious disease, parasitism, malnutrition, injuries, and many other causes of suffering and death in dogs. However, the options are limited for preventing the many diseases of aging. Maintaining a healthy body weight, regular exercise, and a few other lifestyle interventions do reduce risks to some extent, but we need to turn our growing understanding of the mechanisms of aging into therapies that address aging itself.



The direct way to accomplish this is through interventions that prevent or delay the occurrence of specific age-associated diseases. If targeting particular mechanisms of aging can reduce the chances of our dogs developing cancer, for example, this would prolong life and preserve health for many individuals because cancer is a leading cause of death in aged dogs.&nbsp;



However, the immediate cause of death for most dogs is not any specific disease but rather euthanasia. We choose to let our dogs go when it is clear that they are experiencing significant suffering or loss in quality of life.&nbsp;



Aging also leads to a general loss of comfort, function, and resilience, a condition known as frailty. One of the greatest potential benefits of targeting the underlying mechanisms of aging would be to slow the onset of frailty. Keeping dogs biologically younger for longer evwould extend healthspan and could also indirectly lengthen life by delaying the point at which quality of life has declined so much that euthanasia is necessary.&nbsp;



Immortality, of course, seems unlikely for complex biological organisms, and fatal illness or unacceptable frailty is likely inevitable for all dogs eventually. However, there is great potential to improve overall quality of life by compressing the period of significant disease and disability to as small a fraction of the lifecycle as possible and extend those prime, healthy years.&nbsp;

Dogs and humans are uniquely connected as species. Studies have found that 

dogs are even much better than chimpanzees

, our closest evolutionary relatives, at understanding human gestures and communication. For tens of thousands of years, dogs have lived symbiotically with humans, and for at least several hundred years we have intensively bred and shaped dogs to participate in human society. As hunting companions, protectors, and increasingly as members of our close family, dogs are bonded to us and integrated into our lives unlike any other animal.

One consequence of this relationship is that dogs are well-suited to help us understand and manage aging, a biological process with a multitude of factors, many of which are tied to lifestyle and habits. Unlike laboratory animal models, such as rats and mice, dogs share our environments, routines, and the same potential risk factors for death and disease. This makes dogs a more relevant model of natural aging than animals in controlled research settings.

Dogs also share many of the diseases and causes of death as humans. While they grow and age faster than us, they do so in similar ways. Injury and infections, for example, are more common in young dogs as they are in young people, whereas older humans and dogs are more likely to experience cancer or degenerative diseases. These similarities allow research data from dogs to be more readily applied to human health than data from lab animal species. The shorter lifespan of dogs also allows us to study aging and longevity therapies on a more practical timescale than similar studies with humans.

Comparing how dogs and humans age. From 1. Wang T, Ma J, Hogan AN, et al. Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome. 

Another advantage of studying our faithful companions is the fact that intensive breeding in dogs has produced perhaps the greatest degree of variation within any species. This includes physical differences, such as the huge variation in size from the toy breeds such as the Yorkshire Terrier to giants like the Great Dane or Irish Wolfhound, and of course, variation in how dogs age. Large breeds age faster and live shorter lives than smaller breeds. Investigating these differences can give us unique insights into the underlying mechanisms of aging that are harder to identify in other species with less intraspecific variation.

There is also a comprehensive scientific healthcare system in place for dogs as well as humans, which allows not only medical testing and treatment for individual dogs but widespread research on aging and age-associated health problems. There is also ample demand and resources for this research because so many of us love dogs and are willing to contribute time, effort, and money to improving canine health. 

While there are, of course, important biological differences between humans and dogs, our canine companions are uniquely suited to help us understand our own aging. Helping us to understand and alter our own aging is just one more of the many gifts our canine best friends bring into our lives.

Dogs are great models for aging biology

Dogs and humans are uniquely connected as species. Studies have found that <a href="https://www.sciencedaily.com/releases/2012/02/120208180251.htm">dogs are even much better than chimpanzees</a>, our closest evolutionary relatives, at understanding human gestures and communication. For tens of thousands of years, dogs have lived symbiotically with humans, and for at least several hundred years we have intensively bred and shaped dogs to participate in human society. As hunting companions, protectors, and increasingly as members of our close family, dogs are bonded to us and integrated into our lives unlike any other animal.



One consequence of this relationship is that dogs are well-suited to help us understand and manage aging, a biological process with a multitude of factors, many of which are tied to lifestyle and habits. Unlike laboratory animal models, such as rats and mice, dogs share our environments, routines, and the same potential risk factors for death and disease. This makes dogs a more relevant model of natural aging than animals in controlled research settings.



Dogs also share many of the diseases and causes of death as humans. While they grow and age faster than us, they do so in similar ways. Injury and infections, for example, are more common in young dogs as they are in young people, whereas older humans and dogs are more likely to experience cancer or degenerative diseases. These similarities allow research data from dogs to be more readily applied to human health than data from lab animal species. The shorter lifespan of dogs also allows us to study aging and longevity therapies on a more practical timescale than similar studies with humans.



<figure class="wp-block-image"><img decoding="async" src="https://lh5.googleusercontent.com/Y2YiLEfNaIWJ6U3k2-sUHGwAAvCj1izu5LISlDgDe6C5Hg7sAdqdamBhJpL62vh1Ajzgpasm6OAa-70P6gTBzf7p9W5-UraJiN8brzB67zaYBDU_cO5E45k1NzEOJp5ZIDN9i2mr" alt=""/><figcaption>Comparing how dogs and humans age. From 1.&nbsp;Wang T, Ma J, Hogan AN, et al. Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome.&nbsp;Cell Syst. 2020;11(2):176-185.</figcaption></figure>



Another advantage of studying our faithful companions is the fact that intensive breeding in dogs has produced perhaps the greatest degree of variation within any species. This includes physical differences, such as the huge variation in size from the toy breeds such as the Yorkshire Terrier to giants like the Great Dane or Irish Wolfhound, and of course, variation in how dogs age. Large breeds age faster and live shorter lives than smaller breeds. Investigating these differences can give us unique insights into the underlying mechanisms of aging that are harder to identify in other species with less intraspecific variation.



There is also a comprehensive scientific healthcare system in place for dogs as well as humans, which allows not only medical testing and treatment for individual dogs but widespread research on aging and age-associated health problems. There is also ample demand and resources for this research because so many of us love dogs and are willing to contribute time, effort, and money to improving canine health.&nbsp;



While there are, of course, important biological differences between humans and dogs, our canine companions are uniquely suited to help us understand our own aging. Helping us to understand and alter our own aging is just one more of the many gifts our canine best friends bring into our lives.

From birth to physical maturity, there is a rapid increase in function and ability to cope with external stressors in all dogs. Then, as dogs age, health and function begin to decay until death eventually occurs, either directly from a disease or, more often, because humans are forced to make the difficult choice to euthanize a dog because of pain or poor quality of life.  Lifespan is simply the amount of time a dog is alive. Healthspan is the period of life where they are living full, healthy lives, before any major illness or functional decline.

The figure below shows different possible trajectories for a dog’s life. Increasing healthspan means giving dogs more time in good health. A treatment that extends healthspan can slow age-related decline in health and increase this proportion of life spent in good health 

The impact of increasing healthspan on minimizing the period of poor health preceding death. From McKenzie, BA. Lacroix-Fralish, ML. Chen, F. (2022)The phenotype of aging in the dog: A narrative review. J Amer Vet Med Assoc.

In our view, the goal of maximizing healthspan is equally, if not more important than extending lifespan. Therapies which delay death but do not prolong healthspan might actually reduce overall quality of life by prolonging the period of disability preceding death. Giving dogs and their humans more good quality time together means extending the period of good health, not just the length of life. 

Of course, any therapy which extends healthspan will automatically extend lifespan for many dogs because the number one cause of death is euthanasia. If we improve quality of life and function in older dogs, owners will be able to have more joyful time with their canine companions. 

Currently, veterinary medicine tends to focus on diagnosing, treating, and sometimes preventing individual disease. However, the most important underlying cause for nearly all diseases in adult dogs is aging. The most effective way to extend the healthy period of life is to target the basic mechanisms of aging that reduce our function and ability to cope with stress and/or fight off disease. Targeting these mechanisms could potentially prevent 

 heart disease and cancer in many dogs, as well as many other diseases we tend to think of as unrelated. 

Healthspan isn’t easy to measure. What is considered “good health” is subjective. The goal of preventing all age-related changes in function and all disease probably isn’t realistic, at least for now. A more practical approach is to consider the number of age-related illnesses that occur, the age at which they happen, and the overall quality of life dogs experience. If we can find treatments that have a clear impact on these measures, we can say we are extending healthspan, and we are likely to also be extending lifespan by improving quality of life and delaying death from illness and euthanasia. As our understanding of aging in dogs improves, and as we develop better tools to measure health and quality of life, we will continue to make progress towards our goals of extending healthspan and giving dogs and their humans more good time together.

Loyal recruited over 500 dogs to participate in a study assessing two tools for measuring frailty and health-related quality of life in dogs.

Healthspan: the healthy prime of life

<p id="from-birth-to-physical-maturity-there-is-a-rapid-increase-in-function-and-ability-to-cope-with-external-stressors-in-all-dogs-then-as-dogs-age-health-and-function-begin-to-decay-until-death-eventually-occurs-either-directly-from-a-disease-or-more-often-because-humans-are-forced-to-make-the-difficult-choice-to-euthanize-a-dog-because-of-pain-or-poor-quality-of-life-lifespan-is-simply-the-amount-of-time-a-dog-is-alive-healthspan-is-the-period-of-life-where-they-are-living-full-healthy-lives-before-any-major-illness-or-functional-decline">From birth to physical maturity, there is a rapid increase in function and ability to cope with external stressors in all dogs. Then, as dogs age, health and function begin to decay until death eventually occurs, either directly from a disease or, more often, because humans are forced to make the difficult choice to euthanize a dog because of pain or poor quality of life.&nbsp; Lifespan is simply the amount of time a dog is alive. Healthspan is the period of life where they are living full, healthy lives, before any major illness or functional decline.



<p id="the-figure-below-shows-different-possible-trajectories-for-a-dog-s-life-increasing-healthspan-means-giving-dogs-more-time-in-good-health-a-treatment-that-extends-healthspan-can-slow-age-related-decline-in-health-and-increase-this-proportion-of-life-spent-in-good-health-even-if-it-doesn-t-extend-lifespan">The figure below shows different possible trajectories for a dog’s life. Increasing healthspan means giving dogs more time in good health. A treatment that extends healthspan can slow age-related decline in health and increase this proportion of life spent in good health even if it doesn’t extend lifespan!&nbsp;



<figure class="wp-block-image is-resized"><img loading="lazy" decoding="async" src="https://lh3.googleusercontent.com/68eYyrXIDKSaldaOK0yW_tWNHiZwvuDVHgjwZ-SdeBhLSS8AkpHVXvprQVvavaGyGhps9w6PsqHd9LMvFVJcF9rXtV1MKrwN6A4KSC6hZrYnD4l1ft9ZDVi7hrVk1kJ9z58H8S4F" alt="Chart

Description automatically generated" width="1024" height="550"/><figcaption>The impact of increasing healthspan on minimizing the period of poor health preceding death. From McKenzie, BA. Lacroix-Fralish, ML. Chen, F. (2022)The phenotype of aging in the dog: A narrative review. J Amer Vet Med Assoc.</figcaption></figure>



In our view, the goal of maximizing healthspan is equally, if not more important than extending lifespan. Therapies which delay death but do not prolong healthspan might actually reduce overall quality of life by prolonging the period of disability preceding death. Giving dogs and their humans more good quality time together means extending the period of good health, not just the length of life.&nbsp;



Of course, any therapy which extends healthspan will automatically extend lifespan for many dogs because the number one cause of death is euthanasia. If we improve quality of life and function in older dogs, owners will be able to have more joyful time with their canine companions.&nbsp;



Currently, veterinary medicine tends to focus on diagnosing, treating, and sometimes preventing individual disease. However, the most important underlying cause for nearly all diseases in adult dogs is aging. The most effective way to extend the healthy period of life is to target the basic mechanisms of aging that reduce our function and ability to cope with stress and/or fight off disease. Targeting these mechanisms could potentially prevent both heart disease and cancer in many dogs, as well as many other diseases we tend to think of as unrelated.&nbsp;



Healthspan isn’t easy to measure. What is considered “good health” is subjective. The goal of preventing all age-related changes in function and all disease probably isn’t realistic, at least for now. A more practical approach is to consider the number of age-related illnesses that occur, the age at which they happen, and the overall quality of life dogs experience. If we can find treatments that have a clear impact on these measures, we can say we are extending healthspan, and we are likely to also be extending lifespan by improving quality of life and delaying death from illness and euthanasia. As our understanding of aging in dogs improves, and as we develop better tools to measure health and quality of life, we will continue to make progress towards our goals of extending healthspan and giving dogs and their humans more good time together.



<h2 class="has-xl-font-size wp-block-heading" id="loyal-recruited-over-500-dogs-to-participate-in-a-study-assessing-two-tools-for-measuring-frailty-and-health-related-quality-of-life-in-dogs" style="font-style:normal;font-weight:600">Loyal recruited over 500 dogs to participate in a study assessing two tools for measuring frailty and health-related quality of life in dogs.</h2>



<h2 class="has-xl-font-size wp-block-heading" id="read-our-healthspan-study-highlights" style="font-style:normal;font-weight:600">→ <a href="https://blog-admin.loyalfordogs.com/how-scientists-measure-aging-through-healthspan-frailty-and-quality-of-life/">Read our Healthspan study highlights.</a></h2>