Most of us fortunate enough to be blessed with dogs in our lives have had to confront one great limitation in our canine companions-they don’t live as long as we do. Watching bright-eyed, bouncy puppies evolve slowly into creaky, grey-faced old dogs is a painful privilege.
The experience often prompts us to ask “Why?” Why do our beloved dogs have to get old? This is mostly a rhetorical question; more an expression of frustration and regret than a real desire for more information. But while aging, and the loss of comfort and function that typically accompany it, may seem inevitable, it is not incomprehensible. More and more we are learning that aging is a biological process, shaped by evolutionary and guided by internal and external forces that can be understood and manipulated. Immortality for our canine friends may be only a dream, but the more we understand how dogs age, as a species and as individuals, the more we realize there is real hope we may be able to influence how this aging happens, and how our pets experience it.
As with most subjects in science, we shouldn’t really talk about the causes of aging until we have defined the term itself. That is, however, more difficult than it seems. While we think of aging as a universal characteristic of living things, there is actually tremendous variability in how species, and individuals within a species, change physically over time. From the mayfly that lives only a day to tortoises that can live nearly 200 years, animal species vary dramatically in maximum lifespan.
Even within a species, some individuals age faster than others. The longest-living individual dogs have been documented at close to 30 years of age, but most of our canine companions don’t enjoy nearly so much time. Surveys suggest average lifespan can vary from about 6 years in some breeds to 15 years or more in others.
Though it is counterintuitive, time alone turns out to be a poor predictor of aging as a biological process. We can see in our own species that some people may be greying or balding in their thirties while others have full, pigmented hair into their seventies or longer. There are individuals with debilitating arthritis, or other conditions typically thought of as age-related, in early middle age, and then individuals running marathons in their eighties. Aging does happen over time, but many factors besides the passage of time determine how we age.
There is no universally accepted definition of aging. Most scientists studying the phenomenon agree that aging consists of changes, usually deleterious, that occur in individuals over time. These changes often involve the loss of function and an increase in the risk of death. Depending on the specific theory for why aging happens one holds, aging can be seen as the accumulation of damage or the shifting in balance between degradation and production or repair of critical components in the body. Some theories emphasize environmental influences on health and the role of random chance in causing changes in function. Others focus on the role of evolution and how different species have evolved strategies for survival and reproduction that affect longevity. All major approaches to the biology of aging agree, however, that there are specific mechanisms behind the changes we experience as we get older, and that these mechanisms can be understood and potentially altered to influence longevity and health.
Understanding why some breeds and individuals live longer and healthier lives than others is key to understanding aging and how we can influence it. Death may be inevitable for all living things, but research is showing us that the determinants of both lifespan (how long we live) and healthspan (how long we stay healthy) are flexible and can be understood and influenced like other biological phenomena.
My interest in this area has grown over time. As a clinician, many of the most important health conditions I treat, and many of the problems that are life-limiting for my patients, are related to aging. Arthritis pain, loss of muscle strength, and loss of nerve function and coordination are extremely common in older dogs, especially those of larger breeds. These changes frequently have severe negative effects on quality of life, leading to euthanasia. One of my own dogs was in great overall health at 16 years old, which is unusual for a large breed. Unfortunately, progressive arthritis related to age and to congenital dysplasia of several joints eventually left him unable to stand and walk independently, and I ultimately had to let him go because of this, even though he was happy and healthy in every other way.
Cancer is another age-related health problem that I see often in practice. It is one of the leading causes of death in dogs. While there are some identifiable genetic and environmental triggers, the risk of cancer rises dramatically with age. Many of the factors that trigger cancer or protect against it change with age, so even very different types of cancer are connected by underlying mechanisms of aging. Understanding these mechanisms can provide us with tools to prevent many common health problems that might otherwise seem unrelated.
On a personal level, of course, I experience aging like everyone else, in my family members and myself. As a scientist and healthcare professional, I have always been interested in the science of preventing and retarding age-associated health problems, and that interest naturally sharpens as I and those I know get older!
I have recently had an exciting opportunity to get more directly involved in helping to understand aging and its effects on our canine companions. After several months as a consultant, I have joined the team at Loyal for Dogs, also known as Cellular Longevity. This is a small startup company focused on understanding the biology of aging in dogs and developing therapies to reduce age-associated health problems.
Working with Loyal has been a great opportunity for me to learn about aging science. My focus as a clinician has been on prevention and treatment of specific health problems, but less on the common pathways of aging that lead to many of these problems. While I have always practiced preventative medicine, emphasizing with clients the importance of maintaining a healthy weight through proper nutrition and exercise, preventing infectious and parasitic disease through vaccines and other science-based tools, and using what we know about specific risk factors for particular diseases to monitor and detect and treat these as effectively as possible, I haven’t focused as much on the basic science concerning the common mechanisms triggering many age-related diseases. So far, the learning curve has been steep!
As in the past, my goal here is to share what I learn to help pet owners understand the health challenges they may face, the scientific evidence concerning these, and the choices they have available to them. When I pursued my training in acupuncture, I shared the experience through this blog. I have created a new post category for Aging Science, and as I learn about this field, I hope to share more about the subject here. As a result, readers are likely to see an increased in content on the subject of aging biology.
This new opportunity has not, of course, replaced all of my other work. I am still active as a clinician in the same practice I have worked at for over 16 years. I am still involved in promoting evidence-based veterinary medicine (EBVM), and still actively writing about EBVM and science-based pet health in my Veterinary Practice News column and elsewhere. And, of course, I will still be here, following developments in science-based medicine, challenging pseudoscience, and trying to help pet owners navigate claims about alternative therapies for pets.
Since this is my first involvement with a company that is developing, and will perhaps one day be selling, medical therapies for pets, the question will inevitably arise whether this work represents a conflict of interest or somehow undermines my independence as the SkeptVet. People who dislike my critique of specific ideas or medical practices have always resorted to the Pharma Shill Gambit. It is always easier to reject an argument or evidence against one’s claims by dismissing it as “biased” rather than engaging with the argument and evidence directly. In the past, it was easy for me to say that since I had no connections with industry, financial or otherwise, such a claim was not only a fallacious argument but clearly irrelevant.
The fact that I do now have such a connection will undoubtedly embolden such attacks and, in the minds of some, render the last 20 years of my career as a vet and science advocate meaningless. People with such a view are likely so closed-minded and unreachable already, that arguing about the issue would be unproductive. However, I will at least point out that while questions about my objectivity may be perfectly reasonable when I make claims about any therapies Loyal may produce, or about anti-aging therapies and other subjects directly related to my work there, they aren’t a legitimate objection to every argument I make.
Loyal has no control or influence over my work as a clinician or a science communicator, apart from my legal obligation not to give away any proprietary information about their products. No one has even suggested they want to influence what I say as the SkeptVet or in my other advocacy channels. There is no reason for Loyal to care what I say about homeopathy, raw diets, acupuncture, or any of the many other subjects I routinely address since these have no bearing at all on the company’s goals or business interests. My efforts to promote science-based medicine and reduce the harm of veterinary pseudoscience will continue unabated.
I hope my adventure learning about why our dogs age and what we can do about it will be as exciting, interesting, and perhaps useful to you as it is to me. I welcome any questions or suggestions for specific topics in this area. Some of the most interesting subjects I have learned about over the more than 10 years I have been writing this blog have come from you, so keep it up!
With a houseful of ageing animals – cats will be 18 soon, dogs are 11 and 12 – I will be watching with interest. I know their health now is affected by everything that went before (the longevity of their parents, their own diet and exercise and healthcare, all the incidents and accidents that happen over the years, etc) but having coped with hyperthyroidism, arthritis, CKD, and liver failure over the last few years every scrap of solid information to help keep them all happy and reasonably healthy will be gratefully received!
This has always fascinated me too: how come dog/cat/human tissues (eg teeth, joings, liver, kidneys, heart etc) look so similar under the microscope, yet their tissues age so much faster than ours? And if we can find out why, perhaps we can apply that principle to help us age more slowly again? Good luck with these studies, and as always, I really value your writing, so don’t stop, even though it must be near impossible to fit it all in sometimes.
The question that veterinary medicine will not address, is why do German shepherds a century ago, have the same lifespan as now. Having owned 5 dogs, it seems veterinary
medicine, can do nothing more than treat simple problems, diarrhea, urinary tract infections, and the like. When my dogs have been critical, congestive heart failure, easily
treated in humans, in a dog the proper drugs do not work, and your dog dies. My experience is that dogs do not respond the same as humans to the drugs, and illnesses that cause death. In essence, veterinary medicine seems to be good at minor ailments,
and the result is no change in their lifespan. This contrasts to human medicine, where humans live far longer than a century ago. Is the field of veterinary medicine, some what of a hoax, and about making money, when they can not increase the lifespan of your dog.
The assumption behind your views is that dog lifespan is not increasing, but there is no evidence to support that view and some evidence to contradict it. We don’t have anything like the comprehensive data on life expectancy available for humans, but what we do have suggests life and health are, in fact, improving in dogs as they are in humans. And when you say congestive heart failure is “easily treated” in humans and that treatments “don’t work” in dogs, you are unequivocally wrong. Heart diseases, including CHF, are a leading cause of death in humans and far more common in our species than in dogs. And there are many therapies for CHF in dogs that prolong life and well-being extensively. So the questions you ask aren’t answerable because they are based in misconceptions.