I recommend this paper
It is very important and interesting to read Wilson and his colleagues' research on whether stress or proneness to distress is a risk factor for, or a sign of, cognitive decline. They acknowledged that the latter is possible, but favor the idea that chronic distress is a risk factor because distress does not seem to increase in old age, even in Alzheimer's disease.
In more detail, Wilson et al. (2007) found that people who scored high on a test of chronic mental distress were over 40 percent more likely to develop mild cognitive impairment than those who were the most laid back. In a simple proportional hazards model analysis of the prospective data from two large studies of aging and the brain, the risk of developing mild cognitive impairment over a 12-year follow-up increased by over 2 percent for every one-point increase on a measure of chronic distress. The findings come from 1,256 volunteers with a mean age of 76.8 years. The hazard ratio was 1.02, with a 95 percent confidence interval from 1.01 to 1.04.
Nevertheless, depressive symptoms were associated with increased...