Hannum clock

The Hannum clock is a blood-based epigenetic age estimator published by Gregory Hannum and colleagues in 2013. It uses DNA methylation levels at 71 CpG sites, derived from whole-blood samples of 656 individuals, to predict chronological age with a cross-validated correlation of ~0.96. Unlike the Horvath clock, which is multi-tissue, the Hannum clock was trained and validated specifically in blood, making it less generalisable to other tissues. It remains widely cited but has been largely superseded for mortality prediction by second-generation clocks trained on health outcomes.