Big dogs age faster at an epigenetic level, new study finds

Great Danes and mastiffs rarely live more than a decade, while Chihuahuas can live twice as long.

Exactly why big dogs die younger than small ones do has been unclear — but new findings may help to solve that mystery.

The research, published Thursday (Oct.

8) in the journal Science , looked at a chemical code written on top of dogs' DNA.

This code, called the methylome, consists of chemical tags called methyl groups, which bind to DNA's building blocks.

Proteins constantly access DNA, loading up the information written in its code and taking that data away to be turned into new proteins for the cell.

But these methyl groups can act as tiny roadblocks that stop that process in its tracks.

These groups are one type of "epigenetic marker," which collectively help to control gene activity, and their arrangement on DNA changes predictably as animals age, study co-author Blaise Mariner , a bioinformatician at Arizona State University, told Live Science.

Across many studies and species, including humans, scientists have used this data to build epigenetic clocks that track animals' biological ages.

Dogs happen to be a great species for studying aging.

Their owners devotedly track what they eat, how they live, and how their health changes over time.

So Mariner and his colleagues built epigenetic clocks using DNA in blood samples taken from 894 dogs enrolled in the long-term Dog Aging Project based at the University of Washington.

These samples revealed how the dogs' immune cells aged.

These cells patrol the whole body, so "they're a really good measure of systemic aging," study co-author Noah Snyder-Mackler , a genomicist at Arizona State University, told Live Science.