Stress and depression can do more harm than some may think.

Yale University researchers found that chronic stress and depression can cause the brain to shrink and lead to emotional and mental degradation.

Scientists believe stress triggers a genetic switch. That switch then represses genes that are needed to form connections between brain cells, which can lead to the brain getting smaller.

"We wanted to test the idea that stress causes a loss of brain synapses (junctions of nerve cells) in humans," said senior study author Ronald Duman, professor of psychiatry, neurobiology and pharmacology at Yale University.

"We show that circuits normally involved in emotion, as well as cognition, are disrupted when this single transcription factor is activated," he added.

The research team analysed tissue of depressed and non-depressed patients donated from a brain bank and looked for different patterns of gene activation, according to a statement from Yale.

The brains of patients who had been depressed showed lower levels of expression in genes key to brain function.