Obesity and the Canine Life Span

Similar to humans, obesity in dogs has known negative health implications, such as orthopedic issues, diabetes, chronic inflammation, and cancer. White adipose tissue (WAT), which expands when excess calories are available and the body stores as fat, is linked to numerous health issues.

Results of laboratory studies have shown that obesity negatively affects the canine life span. Although it is reasonable to assume the same is true of client-owned dogs, client-owned dogs had never been examined until recently. In a study out of the University of Liverpool, the medical records of middle-aged dogs were examined to determine whether the same associations between being overweight and reduced life span were present.

Study Design

Electronic medical records of 50,787 client-owned dogs from 900 Banfield veterinary practices in North America from 1994 to 2015 were examined in this retrospective, case-controlled study. Data collected included basic signalment, breed, sex, alteration status, age, geographic data, dates of veterinary visits, body weight, body condition score (BCS), reason for death (if available), and date of death. BCSs collected prior to 2010 were categorized as thin, normal, or heavy. After 2010, a 5-category BCS was used. All BCSs collected after 2010 were converted to the 3-category system for data analysis.

Inclusion criteria were as follows: The dogs were neutered, ranged in age from 6.5 to 8.5 years, received uninterrupted veterinary care prior to age 9.5, and had at least 1 veterinary visit with both the owner and pet present. Twelve dog breeds were included: American cocker spaniel, beagle, boxer, Chihuahua, dachshund, German shepherd, golden retriever, Labrador retriever, pit bull terrier, Pomeranian, shih tzu, and Yorkshire terrier. Normal and overweight animals were matched for statistical analyses by sex, year of visit, or patient age using the coarsened exact matching method. Data were cleaned to ensure accuracy and that eligibility criteria were met. Hazard ratios and 99.79% confidence intervals (CI) were analyzed by Cox proportional hazards models. A Bonferroni adjustment was used and significance set at P = .002 in 2-sided analyses.

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Results

Data were available for a median of 3865 dogs in each of the 12 breeds (range: 1273-11,867), and death data were available for a median of 911 dogs per breed (range: 328-4520). BCS hazard ratios ranged from 1.35 (99.79% CI: 1.05-1.73) to 2.86 (99.79% CI: 2.14-3.83) for German shepherds and Yorkshire terriers, respectively. Through binomial testing, the relative risk of death for all 12 breeds examined was significantly increased if patients were “heavy” (P < .001). A time-dependent body condition variable was used in 8 of 12 breeds due to BCSs violating the proportional hazards assumption. The proportional hazards violation occurred at 12.5 years for Labrador retrievers, 10.5 years for shih tzus (could not be reduced), and 14.5 years for all other breeds. In all breeds, survival probability was reduced in overweight patients compared with patients in the normal-weight category.

Conclusion

All canine breeds studied showed a significant association between excess body weight and shorter life span. Although data are not available for additional dog breeds, it is reasonable to assume that being overweight has a negative impact on the overall life span of all dogs. This was a retrospective, observational study, and conclusions as to why investigators saw these associations cannot be made without further investigation.

There were study limitations: client-reported breed and date of birth were not verified, and BCSs were assessed using the dated 3-category scoring system. (Veterinary nutritionists now recommend the 9-category BCS system.) Additionally, investigators used a data matching method, which may increase the likelihood of a type II statistical error. However, the data presented are quite convincing given the level of statistical significance coupled with the high amount of patient data evaluated. Like obesity in people, it is that clear canine obesity is correlated with negative health effects and shorter life span.

Dr. Bohn received her PhD and MS from Georgia State University and has been a practicing veterinary nurse for nearly 20 years. She provides freelance medical writing services through her business, Bohn Communications.