Saliva reveals age secrets: research
Saliva contains the genetic secrets of a person's age, research has shown.
Scientists said analysing a saliva sample could determine an individual's age to within five years.
The US discovery could help crime scene investigations and the development of personalised medicine.
"Our approach supplies one answer to the enduring quest for reliable markers of ageing," said Professor Eric Vilain, from the University of California.
"With just a saliva sample, we can accurately predict a person's age without knowing anything else about them."
The technique depends on a natural process called methylation, which modifies the building-block chemicals that make up DNA.
Methylation patterns shift with age, altering DNA and contributing to age-related diseases.
The scientists identified 88 DNA sites that strongly correlated methylation to age. These were narrowed down to just two genes that had the most powerful age-related links to methylation.
A test based on these two genes made it possible to predict a person's age to within five years.
"Methylation's relationship with age is so strong that we can identify how old someone is by examining just two of the three billion building blocks that make up our genome (genetic code)," said co-author Dr Sven Bocklandt, a former UCLA geneticist now with biotech company Bioline.
The test could be developed into a forensic tool for crime investigators, the scientists said.
By analysing traces of saliva left in a tooth bite or on a coffee cup, experts could get a good idea of a suspect's age.
The technique could also help the development of treatments tailored to a patient's "biological age".
In a minority of the population, methylation does not correlate with chronological, or "birthday", age. Using the saliva test to assess the "bio-age" of these individuals would help physicians evaluate their risk of age-related diseases.
"Doctors could predict your medical risk for a particular disease and customise treatment based on your DNA's true biological age, as opposed to how old you are," Professor Vilain said.
"By eliminating costly and unnecessary tests, we could target those patients who really need them."
The research is published on Thursday in the online journal Public Library of Science ONE.
