Depression May Raise Risk of Alzheimer's

People who have been depressed may be more likely to develop Alzheimer's disease later, a study suggests. The study included 486 people, ages 60 to 90. They did not have any form of dementia when the study began. In the next 6 years, 33 developed Alzheimer's disease. In the study group, 134 people had consulted a doctor because they felt depressed. They were 2.5 times as likely to develop Alzheimer's as others in the study. Researchers said the cause is not clear. More research is needed. The study was published April 8 in the journal Neurology.

What Is the Doctor's Reaction?

A headline on this new study read: Depression Increases Risk of Alzheimer's Disease. If that's true, this study is important. But I think the headline is misleading.

Researchers in the Netherlands did the study. They concluded that people with depression were more likely than people without depression to develop Alzheimer's disease. But that doesn't mean depression directly increases the risk of Alzheimer's disease, as the headline suggests.

There's a big difference between an association and a cause. In this new study, it is possible that depression contributed to the development of Alzheimer's disease. But there are other possibilities.

Perhaps they are linked by a third factor that was not measured. For example, suppose depressed people exercise less than people without depression. In this case, perhaps a lack of exercise (and not depression) contributed to Alzheimer's.

This new study included 486 people between the ages of 60 and 90. They did not have any form of dementia at the start of the study. However, 134 of them reported a history of depression that led them to seek medical advice.

During the next 6 years, 33 people developed Alzheimer's disease. Those with a history of depression were 2.5 times as likely to develop Alzheimer's as those without depression.

If the depression began before the age of 60, the risk of future Alzheimer's disease was 3.7 times higher. Other causes of dementia were also higher among people with a history of depression.

This study raises questions that could alter our understanding and improve treatment of these conditions:

• Does depression damage key parts of the brain involved in memory and language? The study authors looked at two areas, the amygdala and hippocampus. They found no evidence that these areas were abnormal before people developed Alzheimer's disease.

• Could treatments used for depression cause Alzheimer's disease? There's no reason to believe this, but at this point it's impossible to rule out.

• Will this study lead to a better understanding about why Alzheimer's disease develops? If that happens, it could lead to better treatment or prevention of dementia.

We can't answer these questions yet. First, we'll need better proof of whether depression can cause Alzheimer's disease.

This latest study is just a first step. The biggest limitation is that it was small. During the 6 years of the study, only 33 people developed dementia.

In addition, depression was self-reported. It would help to know if their doctors confirmed depression. That's because several things can cause symptoms of depression. These include an underactive thyroid and side effects of some medicines.