Does Depression Mean a Greater Chance of Alzheimer’s?

The Dutch have a wonderful research source – the Rotterdam Study. Part of this large study (several thousands of participants) is the smaller Rotterdam Scan Study, which examines age-related brain changes on MRI; it provided data from just over 500 people aged 60 to 90 at baseline, who were free of dementia at that time. Of these,134 (27%) reported that they had had depression in the past.

The researchers, writing in the journal Neurology, report that during the follow-up period, which averaged 6 years, 33 participants developed Alzheimer’s. Those who had a history of early-onset depression (i.e. before the age of 60) were 3.75 times as likely to develop Alzheimer’s as those who had no depression. In those with a history of late-onset depression the risk of developing Alzheimer’s was only 2.3 times greater than those with no past depression.

The MRI scans showed no apparent differences in size of different brain areas – the hippocampus and the amygdala - depending on previous depression. And the degree of depression was not linked with the occurrence of dementia. The researches speculate that depression may have increased the risk for Alzheimer’s by increasing the activity of a pathway in the brain responsible for corticosteroid production - the hypothalamic-pituitary-adrenal axis. But this is mere speculation, and there is no evidence of a cause-and-effect between the two conditions. Before that can be assumed, a diligent search for a third factor causing both conditions must have proved fruitless.