A team of researchers has looked at three questions:
- Whether a history of depression is associated with an increased likelihood of dementia,
- Whether a first depressive episode earlier in life is associated with increased dementia risk,
- Whether only depressive episodes close in time to dementia onset are related to dementia.
The team looked at depression information from national hospital discharge registries, medical history and medical records, and the dementia had to be clinically diagnosed.
It turns out that there is no link between early depressive episodes and dementia; indeed, they found that each 1-year increase between the onset of depression and the onset of dementia reduced the likelihood of dementia by 8.4%.
However, all is not rosy: there is definitely a relationship between dementia and depression (and this relationship has a long history in academic research). In twin studies they found that twins with prior depression were three times more likely to have dementia than their non-depressed twin.Whilst a depression that first started more than 10 years prior to the onset of dementia is not associated with an increased likelihood of dementia, any depression that was first diagnosed within 10 years of dementia onset was associated with nearly 4 times the likelihood of having dementia, and more than 2.5 times the likelihood of the sufferer going on to develop Alzheimers.
The implication of these findings is that rather than late-life depression being a risk factor for dementia, it may well be an early-warning symptom that dementia or Alzheimers is about to occur.
As for me, it is a relief to know that my long history of depression is not an automatic jail sentence in the prison of dementia.
Brommelhoff, J. A., Gatz, M., Johansson, B., McArdle, J. J., Fratiglioni, L., & Pedersen, N. L. (2009). Depression as a Risk Factor or Prodromal Feature for Dementia? Findings in a Population-Based Sample of Swedish Twins. Psychology and Aging, 24, 2, 373-384
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