A new study has found that people living with major depressive disorder are biologically older than people without depression, and that childhood trauma exacerbates this effect. The results illuminate the epigenetic mechanisms that might explain this discrepancy.

Major depression is one of the most common mental health problems in the United States.

In fact, more than 16 million adults will have had at least one major depressive episode during the past year.

The condition has been linked to various other adverse outcomes, from a shorter life span to a higher risk of cardiovascular problems.

New research shows that major depression may also mean premature aging. Scientists led by Laura Han—from the Amsterdam University Medical Center in the Netherlands—studied the DNA structure of people with depression and made an intriguing discovery.

Han and colleagues found that the DNA of people with major depression is older by 8 months, on average, than that of people who do not have the condition.

The researchers presented their findings at the European College of Neuropsychopharmacology conference, held in Barcelona, Spain, and they published their study in the American Journal of Psychiatry.

This effect of premature aging was more significant in people who had had adverse childhood experiences, such as violence, trauma, neglect, or abuse.

In the US, almost 35 million children have experienced some form of trauma, according to a national survey. That is almost half of the nation's child population.

Studying how depression affects DNA

Han and colleagues examined the DNA of 811 people with depression and 319 people without. The participants were enrolled in the Netherlands Study of Depression and Anxiety.

Using blood samples, the researchers examined how the participants' DNA changed with age. The study revealed that epigenetic changes took place more quickly in people with depression.

Epigenetics is the study of the changes in gene expression that do not affect the DNA sequence. Such changes can occur as a result of many factors, including environment and lifestyle.

One of the mechanisms through which epigenetic change occurs is called DNA methylation—that is, when a methyl group is transferred and added to the DNA.

Overall, the scientists saw that people with major depressive disorder had a degree of methylation and epigenetic change that was indicative of an older age. More specifically, this means that those with depression were biologically older, by 8 months, than people without depression.

In some severe depression cases, this biological age was 10–15 years older than the chronological age.

The study also found that those who had had childhood trauma were biologically 1.06 years older, on average, than people who had not experienced trauma.

The researchers replicated their findings by examining brain tissue samples.

'Epigenetic clock runs faster' in depression

Han comments on their findings, saying, "The fact that we saw similar results in both blood samples and postmortem brain tissue helps support the belief that this is a real effect we are seeing."

"What we see is, in fact, an 'epigenetic clock,' where the patterns of modification of the body's DNA is an indicator of biological age. And this clock seems to run faster in those who are currently depressed or have been stressed."

–Laura Han

"This work shows," she explains, "that methylation levels at specific loci increase and decrease with age, and so this pattern of methylation is a good indicator of biological age. This difference becomes more apparent with increasing age, especially once people move into their 50s and 60s."

The results highlight the biological effect of early-life trauma and the importance of early preventive and therapeutic measures when it comes to depression and adverse childhood experiences.

However, she also points out that more research is needed to strengthen the findings. "Of course," she says, "these are associations, so we need long-term linked studies (longitudinal studies) to be able to draw any conclusions whether the trauma causes the epigenetic aging."