Is Depression a Risk Factor for Dementia?

Do episodes of depression in midlife lead to Alzheimer disease?

Posted Apr 23, 2018

Depressive disorders are common and disabling illnesses. Persons with depression often report poor concentration, cognitive slowing, difficulties with decision making, and problems with memory. Some individuals experience a single depressive episode lasting several months, while others may suffer from recurrent episodes or chronic symptoms.

There are likely many causes of depression. Genetics often plays a role. Environmental stressors may increase the likelihood of a depressive episode.

Some previous research has suggested that persons who experience depressive episodes are at an increased risk of developing dementia when they are older. Other studies have not found a relationship between earlier-onset depression and dementia.

Archana Singh-Manoux and colleagues have revisited this question of whether depressive episodes during middle age or later are related to the development of dementia. They analyzed data gathered during a very large ongoing cohort study in England. The results of their study were published in JAMA Psychiatry.   

Over 10,000 individuals between the ages of 35 and 55 were recruited into the study in the mid-1980s and have been followed for decades. Participants were assessed for depressive symptoms at regular intervals using well-established, self-administered screening questionnaires. Based on scores from these questionnaires, the investigators defined the presence or absence of depressive symptoms.

By 2015, 322 individuals in the study had developed dementia. The investigators examined the depression screening data to determine whether there were differences between people who developed dementia and those who did not. They found that depression during middle age did not increase the risk of developing dementia. This was true even for those who experienced recurrent episodes of depression. However, individuals who developed a dementia were found to have an increase in new depressive symptoms about ten years before a dementia became clinically evident.

There is increasing evidence that brain changes associated with Alzheimer disease begin decades before a clinical diagnosis can be made. A variety of subtle cognitive and behavioral changes have been found to occur during this “preclinical” period, so it isn’t surprising that depressive symptoms appear during this time. The authors hypothesize that the increase in depressive symptoms during the ten years prior to clinically evident dementia is either a prodromal (very early) feature of the dementia or an indication that symptoms of dementia and depression share a common cause.

This is a powerful study because of its longitudinal design and large number of subjects. The results clearly demonstrate that depression during midlife (mid-30s to mid-50s) does not increase the risk for a progressive dementia. Most individuals with midlife depression worry about a lot of things. The results of this study suggest that they need not worry that their depression is leading to dementia.

This post was written by Eugene Rubin MD, PhD and Charles Zorumski MD.

References

Singh-Manoux, A., Dugravot, A., Fournier, A., Abell, J., Ebmeier, K., Kivimaki, M., & Sabia, S. (2017). Trajectories of depressive symptoms before diagnosis of dementia: a 28-year follow-up study. JAMA Psychiatry. 74(7):712-718.