Yes, you are looking for things to worry about. Google brings up many web pages that refer back to the same study. Most of the dementia related to concussion is due to football careers full of concussions and sub-concussive impacts. There is a huge difference between getting literally thousands of sub-concussive impacts with a related number of full concussions from a life of playing football and suffering a single concussion then a few bumps to the head.

If you want to return to running, get some foam ear plugs and run/jog with them in. You will hear the impact of your foot plant and be able to learn a softer gait. With the right shoes and a soft gait, you will be able to run.

Great tip! Conversely, I have always been interested in "natural" running techniques, whereby you essentially go barefoot, and use your calves and feet muscles to absorb the impact of your body, versus cushioning the blow a landing on your heel with more foam. I assume that's the least impactful way to run.