Depression as a modifiable factor to decrease the risk of dementia.

Depression is an accepted risk factor for dementia, but it is unclear if this relationship is causal. This study investigated whether dementia associated with depression decreases with antidepressant use and is independent of the time between exposure to depression and the onset of dementia. We completed a 14-year longitudinal study of 4922 cognitively healthy men aged 71-89 years, and collected information about history of past depression, current depression and severity of depressive symptoms. Other measures included use of antidepressants, age, education, smoking and history of diabetes, hypertension, coronary heart disease, and stroke. The onset of dementia and death during follow-up was ascertained via the Western Australian Data Linkage System. A total of 682 men had past (n=388) or current (n=294) depression. During 8.9 years follow-up, 903 (18.3%) developed dementia and 1884 (38.3%) died free of dementia. The sub-hazard ratios (SHRs) of dementia for men with past and current depression were 1.3 (95% confidence interval (CI)=1.0, 1.6) and 1.5 (95% CI=1.2, 2.0). The use of antidepressants did not decrease this risk. Compared to men with no symptoms, the SHRs of dementia associated with questionable, mild-to-moderate and severe depressive symptoms were 1.2 (95% CI=1.0, 1.4), 1.7 (95% CI=1.4, 2.2) and 2.1 (95% CI=1.4, 3.2), respectively. The association between depression and dementia was only apparent during the initial 5 years of follow-up. Older men with history of depression are at increased risk of developing dementia, but depression is more likely to be a marker of incipient dementia than a truly modifiable risk factor.