Research published in the open access journal Genome Biology explains how the calculator works.
Professor Steve Horvath, of UCLA, used data from 7844 samples in 82 publicly available datasets to create a calculator which predicts the age of healthy tissue using information about changes in DNA methylation. Traditionally, changes to telomeres, the bits of genetic code at the end of chromosomes, are used to tell the age of tissues. Horvath showed that DNA methylation is a much more accurate measure.
DNA methylation is a chemical change that is made to DNA throughout life - previous studies have shown that as we get older, certain changes to the methylation of DNA accumulate. This article demonstrates that, in almost all healthy tissues and cell types, the accumulation happens at a predictable rate and explains how he used the DNA methylation data and the actual age of tissues in 39 datasets to work out that rate and create a calculator.
Some tissue types were shown to buck this trend, however. Breast tissue appeared older while heart tissue appeared younger than expected. Analysis of an additional 5826 cancer tissue samples showed that certain types of brain, breast and colorectal cancers had an accelerated rate of DNA aging, giving hints about how cancer affects tissue and suggesting new methods to diagnose certain cancer types.
Professor Horvath said: "These results are a testimony to the collaborative spirit of the epigenetics community and the benefits of open access to data sets. This study would not have been possible without freely accessible data repositories such as Gene Expression Omnibus, ArrayExpress, and The Cancer Genome Atlas (TCGA)."