Howard Cedar's team shows the body ages one cell at a time

Researchers at the Hebrew University of Jerusalem and Hadassah Medical Center reported in Nature Communications, in findings publicised from 1 August 2026, that ageing does not proceed evenly through the body's tissues. Instead, cells sitting side by side can have very different biological ages. The study was led by Dr. Hagit Masika under Prof. Howard Cedar and Prof. Tommy Kaplan, with Prof. Wolf Reik of Altos Labs and the Babraham Institute in Britain.

Biological age is often estimated from DNA methylation, chemical tags on DNA that shift in predictable ways as we get older. Until now these 'epigenetic clocks' were read from whole tissue samples, averaging millions of cells together. The Jerusalem team instead measured methylation in individual cells, focusing on regions called polycomb CpG islands that tend to gain methylation with age.

They found that tissues are mosaics. Most cells age slowly, while a smaller group switches into a state of accelerated ageing, and rapidly dividing cells are more likely to make that switch. In the tissues examined, cells became more varied as people got older. In a striking illustration, white hairs taken from a person carried an older epigenetic signature than black hairs from the same head.

Cedar, a pioneer of DNA methylation research and a Wolf Prize laureate, told The Jerusalem Post that the findings show the usual way of thinking about ageing is wrong, and that ageing is a mosaic of biologically young and old cells rather than a synchronised process. The researchers suggest ageing is an active biological program rather than random wear and tear, and that diseases of ageing such as cancer and neurodegeneration may begin in a small number of fast-ageing cells. Identifying those cells could allow future drugs to target them directly.