London: A woman's breasts may be the most accurate way yet of identifying a person's age from a blood or tissue sample, as a new study suggests that breasts typically age more quickly than the rest of the female body.
With age, the pattern of chemical markings on our DNA changes.
Each gene becomes more or less methylated, that is, they have methyl chemical groups added or removed.
This generally increases or decreases gene expression, and the process is known as epigenetics.
Steve Horvath at the University of California, Los Angeles, and his colleagues have used these changes to estimate a person's age.
They first performed a detailed statistical analysis of methylation patterns in 7844 healthy tissue samples from 51 different types of tissue. The tissue covered a range of ages - from fetuses to people 101 years old.
The study allowed the team to weed out methylation patterns that varied between tissues, leaving just those that are common to all tissues.
This enabled them to identify a subset of 353 specific regions of the genome that became either more or less methylated with age in almost all types of tissue.
By measuring the total amount of methylation in these regions, the team was able to create an algorithm that identified the age of the tissue.
The team validated the algorithm against thousands more samples of known age.
Horvath said that the method is twice as accurate as the next best method of ageing tissue.
The study is published in the journal Genome Biology.