Dr. Eric Vilain, a professor of human genetics, pediatrics and urology at the David Geffen School of Medicine at UCLA. "With just a saliva sample, we can accurately predict a person's age without knowing anything else about them." Vilain and his colleagues looked at a process called methylation – a chemical modification of one of the four building blocks that make up our DNA.
"While genes partly shape how our body ages, environmental influences also can change our DNA as we age," explained Vilain. "Methylation patterns shift as we grow older and contribute to aging-related disease."
Using saliva samples contributed by 34 pairs of identical male twins ages 21 to 55, UCLA researchers scoured the genomes and identified 88 sites on the DNA that strongly correlated methylation to age. They replicated their findings in a general population of 31 men and 29 women aged 18 to 70.
Next, the scientists built a predictive model using two of the three genes with the strongest age-related linkage to methylation. When they plugged in the data from the twins' and the other group's saliva samples, they were able to correctly predict a person's age within five years – an unprecedented level of accuracy. "Methylation's relationship with age is so strong that we can identify how old someone is by examining just two of the 3 billion building blocks that make up our genome," said first author Sven Bocklandt.