Depression as a modifiable factor to decrease the risk of dementia

Abstract

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.

Figure 1

The figure shows the proportion of men remaining free of dementia over 14 years according to history of depression at the start of the follow-up period. The sub-hazard ratios of dementia associated with past and with current depression were 1.4 (95% confidence interval (CI)=1.1, 1.7) and 1.8 (95% CI=1.4, 2.3).

Figure 2

The figure shows the risk ratio of dementia over a follow-up period of up to 14 years according to history of depression and exposure to antidepressants at study entry (reference: men with no history of depression who were not using antidepressants). The diamonds show the sub-hazard ratio (SHR) of dementia and the whiskers the 95% confidence interval of the SHR. Blue and red diamonds show ratios for men not using and using antidepressants, respectively. The presentation was stratified into no, past and current depression.

Figure 3

The figure shows the risk ratio of dementia according to time of follow-up (⩽5, 5–10 and ⩾10). The diamonds show the sub-hazard ratio of dementia and the whiskers show the 95% confidence interval of the sub-hazard ratio. The blue and red diamonds depict men with past and current depression at study entry, respectively.