We cannot escape from research realities around the human brain anymore. The evidence is increasing at a rapid pace that what we think either diminishes our brain matter or improve it. Mind controls matter. What the actions are we take in the light of these findings is obviously a personal choice. It is a matter of deciding whether I want a healthy, sharp brain right into old age or not. Cultivating mental capacity and resilience is certainly not easy at first but with practice, it becomes easier and the benefits of persistent effort are astounding.
Literally, every thought we have needs to be measured with awareness and vigilance; the quality has to be assessed in terms of whether what we think is brain enhancing or not. Negative thinking, worries about the future and lack of knowledge about how to nurture our brain with healthy thinking, are toxic and stressful. It wears down the architecture of our brain with negative results.
The beauty is however that we can reverse this. The first step towards this would, of course, be to identify and capture toxic thought patterns. A daily quiet period writing in a diary about what we think and feel is perhaps the most useful tool I have ever applied. Give this a try and note your progress. Good luck!