Two meta analysis have shown that depression increases the risk of dementia by two fold. (Jorm AF, 2001, Ownby et al. 2006). The question still is this: Is depression simply a prodromal initial state of dementia or an independent risk factor for dementia years before the onset of dementia?
The Mirage study (Green et al 2008) was the first larger study to investigate the temporal association between depression and dementia. Depressive symptoms were significantly associated with Alzheimer’s disease even when the onset of depression preceded the onset of Alzheimer’s disease by more than 25 years. This finding was recently replicated in two studies [Goveas 2011,Barnes 2012 ) but disproved in two others ( with 4 yrs and up to 15 yrs follow up).
In the Women’s Health Initiative Memory Study including women only, remote history of depression, without current depression, was associated with subsequent risk of probable dementia during a mean follow-up period of 5.4 years.
It is thought that retrospective assessment of prior depressive symptoms and episodes over a lifetime period is an unreliable method. To overcome this limitation, routinely collected longitudinal data bases are used, and they confirm an association between a history of depression and increased risk of dementia.
Patients with many prior hospitalizations for depression had increased risk of subsequently developing dementia compared with those with one hospitalization for depression only. On average, the rate of dementia increased 13% with every episode leading to admission with depression. (Kessing 2004). Psychotic depression and bipolar depression also possibly increase the risk.
Use of antidepressants- would it help or cause it? longitudinal data is lacking. A dutch study (Kessing, 2009) using a large database showed that persons who purchased antidepressants once had a two to three times increased rate of dementia compared with persons unexposed to antidepressants.The rate of dementia changed over time; thus, during the initial prescription periods the rate increased with the number of prescriptions, but continued long-term antidepressant treatment ( SSRI or newer agents) was associated with a reduction in the rate of dementia, although not to the same level as the rate for the general population. When discharged psychiatric hospital patients were followed up, with continued use of SSRIs or newer non-SSRIs, the rate of dementia was not decreased, but use of tricyclic agents was associated with decreased risk. These suggest that use of SSRI or newer agents are limiting/ reducing the risk of dementia in less severe depression and that tricylics might be doing that in severe depression. Antidepressants are now shown to cause neuronogenesis and these observations sit well with that.
Continued use of lithium, which also seems to possess neuroprotective abilities, was associated with decreased risk of developing dementia in bipolar disorder (Kessing 2008, 2011)
Authors conclude that some forms of depressive illness may constitute a long-term risk factor for development of dementia, whereas the onset of depressive symptoms for the first time in old age may reflect a prodromal phase of dementia. Long-term treatment with anti- depressants may influence these associations.
summary of the article:
Depression and the risk for dementia.Lars Vedel Kessing.Curr Opin Psychiatry 2012, 25:457 – 461