Dr. David S. Knopman responds:

Technically, the answer is yes, but not in the way you might think. Depression as a biological disorder does not seem to trigger changes in the brain that make a person more likely to develop Alzheimer's disease or another degenerative brain disorder. Instead, the presence of depression in a person in late mid-life or older age may actually be one of the first signs of dementia. Depression can be caused by many things other than an underlying dementia, but a number of studies have shown that people with depression in late life have an increased risk of becoming demented.

If the question concerns depression in early life or young adulthood, the answer is probably no. But this has been a more difficult question to address and challenging to study. People with severe mental illness in young adulthood often have subsequent life circumstances that are unfavorable, such as low socioeconomic status, complications from medications, prolonged hospitalizations, social isolation, or great interpersonal upheaval. Thus, people with early life depression also have many other factors that contribute to risk for dementia apart from the depression itself.