Cells turn biologically older in people who are severely depressed or who have been in the past, according to a report released on Tuesday in the journal Molecular Psychiatry.
Josine Verhoeven from the VU University Medical Centre in the Netherlands, along with colleagues from the US, recruited 2,407 people to take part in the study.
More than one third of the volunteers were currently depressed, a third had experienced major depression in the past and the rest had never been depressed.
The volunteers were asked to give a blood sample for the researchers to ana-lyse in the lab for signs of cellular ageing.
The researchers were looking for changes in structures deep inside cells called telomeres. As cells divide, the telomeres get shorter and shorter. Measuring their length is a way of assessing cellular aging.
People who were or had been depressed had much shorter telomeres than those who had never experienced depression.
Furthermore, the most severely and chronically depressed patients had the shortest telomeres.
"This large-scale study provides convincing evidence that depression is associated with several years of biological ageing, especially among those with the most severe and chronic symptoms," said Verhoeven and his colleagues.