One of the first logical questions for a good skeptic to ask when thinking about canine aging biology is whether it is plausible that we can extend lifespan (years lived) and healthspan (healthy years lived) in dogs. Is there reliable evidence that aging is not something immutable and inevitable but something we can actively alter? If so, how strong is that evidence, what does it suggest we should try, and what do we still need to learn?
The good news is that there are decades worth of research showing that lifespan can be extended and age-associated disease reduced in a variety of species. Much of this research has involved lab animals, such as roundworms, fruit flies, and mice. Such studies are useful for understanding basic principles in bilogy, and they suggest hypotheses to test in other species, but they aren’t sufficient to prove a given treatment or preventative intervention will work. There are even some laboratory studies in dogs that strengthen the basic understanding of aging and how we might influence it, but again this only gets us so far.
Fortunately, we have more than this. While we can’t predict whether specific drugs or many other treatments will work until we’ve done the science to test them, we know that healthspan and lifespan can be extended in dogs because it’s been done! The one method that has been shown effective in many different animals, including dogs, is dietary restriction.
Dietary restriction is defined as a reduction in calorie and nutrient intake without malnutrition. The specific details vary among studies, but in general the key appears to be reducing total calorie intake significantly (perhaps 20-40%) without inducing micronutrient deficiencies. There are some other strategies that have proven effective or appear promising (e.g. changes in protein intake, intermittent fasting), but overall the best evidence is for total calorie reduction.
The good news is that there is strong evidence for the benefits of calorie restriction in dogs. One long-term study in Labrador retrievers paired littermates by sex and weight and then randomly assigned one to unrestricted feeding and the other to a calorie intake 25% less than it’s paired littermate. In order to avoid obesity in the control dogs, at about 3 years of age the protocol was changed so these dogs were fed to maintain an optimal body condition rather than ad libitum, but the calorie-restricted dogs were still fed 25% less than their paired littermates ate. The study ran until the last dogs died.
The calorie restricted dogs had a medium lifespan of 13 years, 16% longer than the 11.2 years in the control group. Calorie restricted dogs also developed arthritis 1.5 years later on average than the control dogs. Some dogs developed cancer in both groups, but the average age of death from this cause was 2 years later in the restricted calorie group (11.6 years vs 9,7 years).
There is, unfortunately, also bad news. Dramatic, lifelong caloric restriction is not a practical method of extending lifespan and healthspan in dogs, primarily because it is too difficult for dog owners to control their feeding practices appropriately. Obesity is a tremendous and growing problem in companion dogs. We seem unable to feed our dogs appropriately even to maintain a healthy weight, so the chances that we will succeed in restricting their calorie intake sufficiently to obtain significant lifespan and health benefits seem low. Food is part of how we express love for our animal companions, and rational feeding practices are surprisingly tough to implement.
Fortunately, there may be alternatives. Studies of dietary restriction have taught us a lot about the fundamental biology of aging, and there are many potential means to achieve some of the benefits of caloric restriction other than feeding dramatically less food to our dogs. The composition of diets, the timing of feeding, and medicines which mimic aspects of the physiologic response to dietary restriction are all promising avenues of research.
While no clearly effective anti-aging therapy is yet available, we have already proven that aging can be influenced. There are many different ongoing research efforts aiming to translate the decades of knowledge concerning aging biology into more, healthier years for our dogs. Science will ultimately tell us which, if any, will work and what the relative risks and benefits will be, as is always the case, but having a plausible hypothesis and established potential mechanisms is a good first step.