Big dogs may burn through life faster at the molecular level, not just on the clock. A study in Science used blood samples from nearly 900 canines participating in the Dog Aging Project to build “epigenetic clocks”—molecular measures of biological age based on chemical tags, called methyl groups, that sit atop DNA, per Live Science. Researchers found that larger dogs’ clocks tick faster: For each calendar year, their cells aged more than those of smaller dogs. A key difference showed up in “jumping genes,” or transposable elements. In big dogs, crucial methyl tags that usually keep these genes quiet were more likely to fall away, potentially letting them activate and stir up inflammation tied to aging.
The work also suggests dogs’ immune cells lose some of their specialized identity as they age, which may weaken defenses against disease. Scientists suspect breeding for rapid growth and large size may have come at a biological cost, though that trade-off remains a hypothesis. Next up: refining these molecular clocks so vets and owners can better predict age-related health risks, as well as possibly glean clues about human aging, since dogs share our homes and environmental exposures.