People who suffer from recurrent depression could find a critical part of their brain responsible for forming memories shrinking over time, according to a new study. The findings have implications for the long-term health of those who suffer from the disease, especially for children and young adults.

Fifteen research institutes from around the world, including those from the United States, Europe and Australia, combined the results of their own data on the hippocampuses of depressed and healthy people. They examined the brain magnetic resonance imaging results of 8,927 people, of whom 1,728 had major depression. Their results were published Tuesday in the journal Molecular Psychiatry.

They found that 65 percent of the depressed subjects suffered from recurrent depression, and that these people also had a smaller hippocampus, which is responsible for forming long-term memories and connecting them with emotions. People who had only experienced one depressive episode were found to have a normal-sized hippocampus.

“So recurrent or persistent depression does more harm to the hippocampus the more you leave it untreated. This largely settles the question of what comes first: the smaller hippocampus or the depression? The damage to the brain comes from recurrent illness,” Ian Hickie of the University of Sydney, who led the study’s Australian arm, told the Guardian.

He added that the study’s findings meant that people who suffered from depression at an earlier age were more at risk, since it meant that those who began suffering the effects of depression, which include social withdrawal and reduced performance at school or work, were likely to suffer more episodes in future.

"Clearly if you start [getting depression] younger, the chance that you have more episodes is increased. ... It will go on damaging the brain and it will make the function of that organ worse," Hickie said.

However, due to recent advances in brain science, scientists now believe that many changes in the brain are reversible, with treatment and medicine. “Other studies have demonstrated reversibility, and the hippocampus is one of the unique areas of the brain that rapidly generates new connections between cells, and what are lost here are connections between cells rather than the cells themselves,” Hickie said.

In addition, researchers also found that the hippocampuses of people who were taking antidepressants were larger, implying that the drugs could have a protective effect. “There is a lot of nonsense said about antidepressants that constantly perpetuates the evils of them, but there is a good bit of evidence that they have a protective effect,” Hickie said.