The companion dog as a model for human aging and mortality

Abstract

Around the world, human populations have experienced large increases in average lifespan over the last 150 years, and while individuals are living longer, they are spending more years of life with multiple chronic morbidities. Researchers have used numerous laboratory animal models to understand the biological and environmental factors that influence aging, morbidity, and longevity. However, the most commonly studied animal species, laboratory mice and rats, do not experience environmental conditions similar to those to which humans are exposed, nor do we often diagnose them with many of the naturally occurring pathologies seen in humans. Recently, the companion dog has been proposed as a powerful model to better understand the genetic and environmental determinants of morbidity and mortality in humans. However, it is not known to what extent the age-related dynamics of morbidity, comorbidity, and mortality are shared between humans and dogs. Here, we present the first large-scale comparison of human and canine patterns of age-specific morbidity and mortality. We find that many chronic conditions that commonly occur in human populations (obesity, arthritis, hypothyroidism, and diabetes), and which are associated with comorbidities, are also associated with similarly high levels of comorbidity in companion dogs. We also find significant similarities in the effect of age on disease risk in humans and dogs, with neoplastic, congenital, and metabolic causes of death showing similar age trajectories between the two species. Overall, our study suggests that the companion dog may be an ideal translational model to study the many complex facets of human morbidity and mortality.

Keywords: aging; cause of death; comorbidity; companion dog; human; mortality.

Figure 1

Survivorship (a) and hazard curves for (b) for human (left) and dogs (right). Human data are from the U.S. Census Bureau (1972–2002), and canine data come from the VetCompass database (2010–2013). For both species, colors represent the two sexes, female (red) and male (blue). Gompertz slope parameters were calculated for humans: 0.089 (females) and 0.080 (males), and dogs: 0.0214 (females) and 0.0219 (males)

Figure 2

Correlation between pathophysiological process (a), organ system (b), and specific cancer (c) causes of death in humans and dogs in the VMDB database (1984–2004). (a) Correlation p = .58 by Spearman rank test, ρ = 0.238. Removing vascular causes of death results in a significant correlation between humans and dogs (ρ = 0.857, p = .023). (b) Spearman rank ρ = 0.733, p = .031. (c) For those causes of death that had a “neoplastic” process, graph depicts the organ systems in which cancer occurred. Spearman rank ρ = 0.661, p = .053

Figure 3

Proportions of human and dog pathophysiological process causes of death with age. Humans are represented in red with dogs in blue. Dashes indicate 95% confidence intervals

Figure 4

Proportions of human and dog organ system causes of death with age. Humans are represented in red with dogs in blue. Dog years have been rescaled to approximate human years as described in Methods. Dashes indicate 95% confidence intervals

Figure 5

Stacked density plots of pathophysiological process causes of death with age for humans (top) and dogs (bottom). Congenital causes of death in humans were too small to be visible in the figure

Figure 6

Stacked density plots of organ system causes of death with age for humans (top) and dogs (bottom)