People with depression are more likely to later develop Alzheimer's disease, according to two studies published on Monday, and one team said that chronic stress may damage their brains.

Some researchers have assumed that Alzheimer's causes depression, so Wilson's team tracked 917 retired Catholic priests and nuns, 190 of whom developed Alzheimer's disease. Those with more symptoms of depression at the beginning of the study were more likely to develop Alzheimer's disease

But Wilson's group did not find a sudden onset or worsening of depression in the few years before symptoms of the brain disease took hold

Wilson cited one theory that chronic stress from depression releases excessive amounts of the brain hormone cortisol that ultimately damages the filigreed connections between brain cells called dendrites

among the 134 of 503 people in the study who reported seeking help for depression, the risk of Alzheimer's was 2.5 times higher than among those who were not depressed