Over time, tiny molecules glue themselves to the DNA in cells. These so-called epigenetic (on top of the genome) modifications can affect which genes are expressed in particular cells.31 Because environmental factors like diet, stress, and exercise partly influence epigenetic modifications, the older we are, the more of them we accumulate.32 Most epigenetic modifications are harmless, but the more you have for a given age, the higher your risk of dying.
