Saliva contains many useful components. Lubricants. Enzymes for breaking down food. And now, compounds that can reveal a person’s age. That’s according to a study in the journal Public Library of Science ONE. [Sven Bocklandt et al., "Epigenetic Predictor of Age"]

During normal development, DNA in your body gets what’s called methylated. Small chemicals called methyl groups bind to the DNA, helping to determine which genes become active. But the patterns of methylation change as we grow older. Which was a clue that measuring methylation might give away age.

The researchers studied DNA in saliva contributed by 34 pairs of male identical twins, ages 21 to 55. They found 88 sites on the men’s DNA where the amount of methylation correlated with their ages. The scientists next verified that finding in 60 men and women, ages 18 to 70.

Then they narrowed in on two genes that had the strongest age-related correlation. And using just that data, they found that they could estimate the ages of their saliva contributors to within five years.

This technique might help in crime scene investigations—recovered saliva could tell the age of a perpetrator. So if you’re worried about anyone knowing how old you are, be careful where you spit.

—Cynthia Graber

[The above text is an exact transcript of this podcast.]