Depression and Dementia
One of the symptoms of depression is a loss of thinking ability. A history of recurrent depression has been linked to an increased dementia risk. The ways depression leads to mild loss of thinking skills include sleep disruption, apathy, and medication side effects. Depressed individuals perform worse on cognitive tests such as information processing speed, selective attention, executive function, and the ability to learn and recall new information. It isn’t clear what the causal relationship between depression and dementia is and many factors may contribute.
Depression may be a an early sign of dementia, especially if it occurs later in life. It also could be an independent contributor to dementia risk through a biologic influence on the brain. In older adults, risks such as hypertension, diabetes mellitus, or atrial fibrillation may influence the development of both depression and cognitive impairment. Deficits such as delayed processing speed, executive dysfunction, and apathy are common in those with depression later in life. These symptoms are linked to underlying disease in the frontal and subcortical regions of the brain.
Depression has been associated with many drugs commonly used by the elderly. (Drugs associated with depression include beta blockers, such as Methyldopa, Amantadine, and Beta interferon; Calcium channel blockers, such as Clonidine, Metronidazole, Prazosin, Reserpine, and steroids. Cognitive impairment has also been associated with the use of antidepressants, especially tricyclic antidepressants such as Amitriptyline, Nortriptyline or benzodiazepine.) Several studies have shown a higher risk of dementia among individuals with a history of depression as much as 10-25 years before the onset of dementia. Recurrent bouts of depression may be even worse as they have been associated with a 14% increase in risk for all-cause dementia. Adults with a history of chronic depression may have more selective deficits in memory caused by a reduction in the size of the part of the brain that stores memory (the hippocampus). Regardless of the mechanism, population studies have shown that eliminating depression from the elderly population can reduce the number of new cases of dementia by an estimated 10% over 7 years.
 Mast BT, Yochim B, et.al., Risk factors for geriatric depression: the importance of executive function within the vascular depression hypothesis. J Gerontol A Biol Sci Med Sci 2004;59:1290-1294.
 Potter GG, Steffens DC, Depression and cognitive impairment in older adults. Psychiatric Times 2007; 24(13):23-30.
 Dotson VM, Beydoun MA, Zonderman AB, Recurrent depressive symptoms and the incidence of dementia and mild cognitive impairment, Neurology 2010, 75(1)
 Sheline Yi, Sanghavi M, et.al., Depression duration but not age predicts hippocampal volume loss in medically healthy women with recurrent depression. J Neurosci, 1999;19:5034-5043.
 Ritchie K, Ritchie CW, Berr C, et.al., Designing prevention programmes to reduce incidence of dementia: prospective cohort study of modifiable risk factors, BMJ 2010; 341:c3885