No spitting or you'll give your age away

A saliva sample can determine a person's age to within five years, according to research published in the journal PLoS One. The technique relies on a natural process called methylation, a chemical change to one of the four building blocks that make up DNA. Methylation patterns shift with age, altering DNA and contributing to age-related diseases.

Lead scientist Dr Eric Vilain, a professor at the University of California, Los Angeles (UCLA), said: 'Our approach supplies one answer to the enduring quest for reliable markers of ageing'.

'With just a saliva sample, we can accurately predict a person's age without knowing anything else about them', he added.

Researchers from UCLA studied DNA in saliva from 34 pairs of identical male twins, ages 21 to 55. They identified 88 sites on the DNA where the amount of methylation correlated with their ages. The findings were then replicated in a general population of 60 men and women, ages 18 to 70. Narrowing down their search, the team designed a predictive model using two of the three genes with the strongest age-related links to methylation, and were able to correctly predict the person's age 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', said first author Dr Sven Bocklandt. 

The method could help in crime scene investigations and in the development of personalised medicine. Scientists could establish a person's 'bio-age', the measurement of a person's biological age versus their chronological age. In a minority of the population, methylation does not correlate with chronological age. Therefore, by using the saliva test to assess the 'bio-age' of these individuals, clinicians could 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', explains Dr Vilain. 'By eliminating costly and unnecessary tests, we could target those patients who really need them', he added.

The UCLA team is currently exploring whether people with a lower 'bio-age' live longer and suffer less disease or whether a higher 'bio-age' is linked to a greater rate of disease, as well as early death.