It turns out that chocolate is bad for dogs in more ways than one—if the dog in question is a chocolate Lab.

New research found that chocolate-colored Labrador retrievers don’t live as long as black or yellow Labs. They’re also more prone to ear infections and skin diseases.

Those are among the findings of a new study published last week in the journal Canine Genetics and Epidemiology by researchers at the University of Sydney in Sydney, Australia.

The research team analyzed 33,000 veterinary patient records from the UK. Almost half of the Labrador retrievers were black, just over a quarter were yellow, and just under a quarter were classified as chocolate (or liver, often used to describe the lighter end of that color spectrum).

The average lifespan of black and yellow Labs was 12.1 years. For chocolate Labs, it was 10.7, a difference of more than 10%. Musculoskeletal disorders and cancer were the most common causes of death regardless of coat color. The most common disorders affecting the breed overall were ear and joint conditions, and obesity.

But coat color came into play for a couple of non-life-threatening conditions.

The prevalence of ear inflammation was twice as high in chocolate Labs, who were also four times more likely to suffer some kind of dermatitis than black or yellow Labs. They also had double the number of hot spots on their skin.

It’s not what the researchers were expecting.

Lead researcher Paul McGreevy, BVSc, PhD, MRCVS, MACVS (Animal Welfare), professor of animal behavior and animal welfare science at the University of Sydney’s Faculty of Veterinary Science, told NEWStat that “The color-related predispositions were a surprise. We found nothing similar in pugs, who can be black or fawn, or Cavalier King Charles spaniels, who can be [either black, white, and tan, or chestnut and white].

Which isn’t to say that the dogs’ chocolate color is causing the problems. More likely: it’s the long-term cumulative effects of pet owners’ desire for a dog of that luscious chocolate color.

“The relationships between coat color and disease may reflect an inadvertent consequence of breeding certain pigmentations,” McGreevy said.

In other words, selective breeding for the popular chocolate color may have inadvertently introduced genetic consequences for the dogs’ health: That color is a recessive trait, meaning that to produce a chocolate-colored puppy, both parents must have the gene that produces that color.

It’s not the first time that coat color has been linked with health in certain animal species—some researchers suspect that the same gene that codes for black fur instead of brown in wolves might also be related to fighting infection and reducing inflammation—in part because the same protein produced by that gene has been linked to inflammation and infection in humans.

Which could explain the relationship between coat color and the predisposition to health problems in chocolate Labs.

“Research in humans has suggested a link between inflammation and both life expectancy and quality of life,” McGreevy said. “Perhaps by a similar process, the repetitive inflammatory skin and ear infections to which we found chocolate dogs prone accumulate to create an immunological burden that effectively shortens their lives.”

If people called them liver Labs, they’d probably be less popular.

Solid black was the preferred coat color when Labrador retrievers first emerged as a distinct breed in the mid-1800s. Yellow and chocolate puppies occasionally appeared in litters, as did white spotting, but breeders selected for black because that’s what the public wanted; yellow or chocolate offspring were usually culled. The first officially recognized yellow Lab was born in 1899, and while chocolate Labs became more accepted in the 1930s, they didn’t really catch on with pet owners until the 1960s.

That late-blooming popularity may have contributed to the overbreeding of less genetically robust bloodlines—and dogs who are more predisposed to skin and ear conditions.

Not to mention a shorter lifespan.

For veterinarians who might find themselves dealing with frantic phone calls from worried chocolate Labrador retriever owners, McGreevy had this advice: “It’s worth reminding owners that this was a study of Labrador retrievers in the UK and . . . .this report doesn’t mean that every chocolate Lab will die earlier than their black or yellow counterparts.”

As McGreevy points out, “Veterinarians are trained to understand the nature of statistical studies.” Pet owners are not. So it’s understandable if they get a little worried when they read about findings like these in the media.

McGreevy emphasised that the study was by no means definitive and added that further research was being done: “We’re currently undertaking a parallel study of Labrador retrievers in Australia to establish whether or not these color-related differences persist in the relatively isolated Australian population. If we fail to find the same differences, this may point to the overuse of certain breeding lines in the UK.”

And as always, findings should be taken in context.

Overall, Labrador retrievers are one of the longest-living dog breeds, at least in the UK: According to a recent study of mortality rates in UK dogs, the median age of death in all breeds is 10.33 years.

Which still puts chocolate Labs, at 10.7 years, ahead of the pack.

Photo credit: © iStock/lizcen