Although clinical depression has been linked to other mental disorders, a newly published study indicates the illness also has effects on physical health—specifically the aging process.

According to the study published by Nature, researchers at the University of California-San Francisco have found Major Depressive Disorder (MDD) could accelerate aging at the cellular level and potentially lead to a premature death. The team behind the study analyzed blood samples from more than 100 people: 60 of the subject's did not have depression and 49 were living with MDD without treatment. Researchers examined the samples’ methylation patterns using the “GrimAge” clock, which is believed to be the most accurate indicator of an individual’s remaining lifespan. 

The study found the epigenetic clocks among depressed subjects were, on average, about two years older than those of healthy controls who were the same chronological age. Researchers noted the subjects with MDD had not shown any physical signs of accelerated aging, and confirmed they accounted for lifestyle factors such as smoking and body mass index.

“This is shifting the way we understand depression, from a purely mental or psychiatric disease, limited to processes in the brain, to a whole-body disease,” said UCSF student Katerina Protsenko, who was also the lead author of the study. “This should fundamentally alter the way we approach depression and how we think about it—as a part of overall health.”

Previous studies have yielded similar results. In 2013, researchers from the Netherlands found those with depression had shorter telomeres—chromosome “caps” that shorten with age. A 2018 study also found people diagnosed with depression experienced faster rates of cognitive decline, leading experts to believe the mental illness may cause the brain to age faster.

“As we continue our studies, we hope to find out whether addressing the MDD with anti-depressants or other treatments alters the methylation patterns,” said UCSF professor Dr. Synthia Mellon, a co-senior author of the study. “… [This] would give us some indication that these patterns are dynamic and can be changed.”