How scientists measure aging through Healthspan, frailty and quality of life

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Brennen McKenzie, MA, MSc, VMD
by Brennen McKenzie, MA, MSc, VMD

Loyal has just published the results of our Healthspan study, the first clinical study assessing two tools for measuring frailty and health-related quality of life in dogs.

Dogs are a unique translational model of aging. By understanding aging in dogs, we learn how to better treat aging in both dogs and humans. We observed groups of young and old dogs and small and large dogs using a veterinarian assessment tool — the Canine Frailty Index, or CFI — to measure frailty and an owner assessment — VetMetrica’s Health-Related Quality of Life (HRQL) questionnaire — to measure quality of life.

Our core mission here at Loyal is to give people and their dogs more time together. By targeting the underlying mechanisms of aging, we are working to help dogs live longer. But for that to be a truly worthwhile goal, we have to do more. We have to make that additional time enjoyable and worth living. 

Studying healthspan aims to measure dogs’ function towards their end-of-life

We want to extend lifespan but it is critical that we extend healthspan, the period of time dogs are living healthy lives, too. We want dogs to live healthy lives for as long as possible, before aging has diminished their function or quality of life. 

Frailty is a state of increased vulnerability to disease and death. Health-related quality of life is a measure of the impact health problems have on overall wellbeing. These two facets of aging are commonly measured in older humans to help guide lifestyle and healthcare decisions.

Veterinarians are only just beginning to give more consideration to how frailty and the impact of health problems on quality of life are manifestations of the aging process in dogs, and the tools to measure these are not yet in routine clinical use.

What tools were used to evaluate frailty and quality of life?

We used two existing tools for evaluating older dogs; the Canine Frailty Index (CFI) and the Vetmetrica Health-related Quality of Life questionnaire.

Using the CFI, a veterinarian can evaluate a wide range of age-related problems and assess the overall impact of aging on the health and function of an individual dog.

The HRQL is a questionnaire that assesses owners’ perceptions of their dog’s quality of life. It evaluates this in several different domains, including energy and enthusiasm, happiness and contentment, calmness and relaxation, and the dog’s level of comfort and activity.

A graphical summary of the Healthspan study

Who participated and how did we run the study?

In our Healthspan study, Loyal recruited 586 dogs from across the United States.

We had 84 different breeds — representatives of the purebred Cane Corso, French Bulldog, and Great Dane; and many Boxers, Australian Shepherds, Golden Retrievers, poodles, doodles and supermutts.

We saw dogs from 2 years old to 18, and dogs ranging from less than 15 to over 120 pounds. We even enrolled a tiny dog just under 3 pounds and a giant 175-pound dog.

We analyzed 451 of these dogs to test how well the CFI and HRQL tools measured the effects of aging in both young and old dogs. We also compared small and large dogs using these tools, to better understand the different way aging impacts dogs of different sizes. 

The dogs in the Healthspan Study came with their owners to our clinical sites for an examination and collection of blood samples. These sites were at small private veterinary hospitals, large academic medical centers, and even our innovative “pop-up” mobile clinical site. The dog owners in the study also answered detailed questions about their health. 

Our results: frailty in old and young dogs

Using this information, we were able to show that the CFI is a sensitive tool for detecting the negative health impact of aging on dogs. These scores were higher in the old dog group and began to increase after 7 years of age.

CFI scores increased with age in older dogs but are stable in younger dogs. Based on Figure 4 from the study publication

Our results: quality of life in old and young dogs

We were also able to confirm that the HRQL is an effective measure of the impact of aging on health and quality of life. Generally, we found that HRQL scores decreased with age. HRQL scores were lower in older dogs than in the younger group due to the accumulation of age-related health problems and the effects of these problems on the overall quality of life in these dogs.  Just as with the CFI, the scores for the HRQL got worse with age in the older dogs but stayed at a better level in the younger, healthier dogs.

HRQL total scores decrease with age. Total scores are shown in young/old small (blue) and young/old large dogs (red) through these box and whisker plots. Boxes demonstrate the center and spread of scores in each group. The horizontal bars demonstrate the groups that are significantly different from each other. The study had some outlier values, indicated by the dots. Based on Figure 5a from the study publication

Our results: quality of life in large and small dogs

When we analyzed the different components of the HRQL, we also found that there were some differences between large and small dogs. It is well-known that large dogs have shorter lives than smaller dogs, and it is believed this is because they experience the negative health effects of aging sooner and more severely. 

The HRQL’s four domains include energy and enthusiasm, happiness and contentment, calmness and relaxation, and the dog’s level of comfort and activity. We observed HRQL scores are stable in young dogs, but starting at age 7, old dogs show yearly declines in HRQL scores across most domains. 

We were able to show, for the first time, significant differences in activity and comfort between older large and small dogs. All dogs experience a decline in activity and perceived comfort as they age, but this decline is faster in bigger dogs, as measured by the Active/Comfortable component of the HRQL.

HRQL scores are stable in young dogs, but starting at age 7, old dogs show yearly declines in HRQL scores across most domains. In activity and comfort scores, we observed that larger dogs showed faster yearly declines compared to small dogs. Based on Figure 6b from the study publication

Vet assessments vs owner questionnaires

Another important finding of the Healthspan study was that the CFI and HRQL both identified the same age-related changes even though the CFI was a medical assessment by a veterinarian and the HRQL was a questionnaire evaluating the owners’ perceptions of their dogs at home. This consistency is strong evidence that the tools are both measuring the same underlying process—that is aging! 

These complementary tools can also be used to help better understand the details of the aging process in dogs. For example, the fact that larger dogs showed a greater decline in the Active/Comfortable component of the HRQL makes sense when we see that in the list of diseases that make up the CFI, arthritis was more common among the large old dogs than among the smaller dogs. It is likely that the earlier and more rapid development of this common age-related health problem may be part of the explanation for why this aspect of health-related quality of life declines faster in bigger dogs. 

How the Healthspan study builds on the Loyal mission

Building on the success of the Healthspan study, Loyal will use the HRQL and the CFI in future studies to help us better understand canine aging and evaluate the impact of our drugs on healthspan in aging dogs. Helping vets and dog owners to measure the effects of aging on dogs and developing drugs that can slow aging mechanisms are critical to our core mission of extending lifespan and healthspan in dogs and giving people and their canine companions more joyful time together.

Read the full publication in GeroScience.


Chen, F.L., Ullal, T.V., Graves, J.L. et al. Evaluating instruments for assessing healthspan: a multi-center cross-sectional study on health-related quality of life (HRQL) and frailty in the companion dog. GeroScience (2023).

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