The goal of longevity therapies is to prolong both lifespan (the number of years an individual lives) and healthspan (the number of years free of significant disease or disability). Current preventative medical interventions, such as vaccines, have greatly increased lifespan, mostly by preventing death early in life. Medical treatment of age-related diseases also prolongs lifespan by delaying death, and it can increase healthspan somewhat by reducing the negative impact of disease on quality of life.
Unfortuntely, increases in lifespan driven by reduction of early-life mortality have exceeded increases in healthspan, and the period of disability and diminished quality of life preceding death has grown. This is clear for humans and appears true for dogs as well.
The length of life for dogs varies with breed, size, neuter status, and other variables. Lifespan ranges from an average of 6-10 years for the shortest-lived breeds up to 14-18 years for longer-lived dogs.
Regardless of the number of years lived, all dogs progress through a lifecycle that involves changes in physiologic resilience and functional capacity over time (see figure above). There is a rapid increase in function and ability to cope with external stressors from birth to physical maturity. The inevitable decline in health and function from this point can occur along variable trajectories.
The purpose of interventions to promote healthy aging is not only to increase the number of years lived but to maximize the period of good health and confine the loss of resilience and functional capacity to the shortest possible period. Therapies which delay death but do not prolong healthspan can reduce overall quality of life by prolonging the period of disability preceding death. Learning to quantify the impact of aging on health will enable us to better assess the impact of interventions on both lifespan and healthspan and achieve the greatest benefits for our dogs.
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