I have not read any studies or seen any newscasts but I can tell you MY experience. About a year ago I started drinking WAY too much diet soda and really have no excuse or explaination- I think it was the caffeine as I am not a coffee drinker. I was drinking 2-3 cans a day (which is too much in my opinion). Prior to that I would drink regular soda, maybe a can a day and never had any problems.
I started having dizzy spells, light sensitivity, migranes, ringing in my ears. heart palpitations, forgetfulness, difficulty forming sentances, visual disturbances all kinds of crazy stuff was happening and the doctors couldn't figure out the cause, my primary care doctor was convinced I had MS.
One day I had a crazy event which I can only describe as a siezure- I was walking through a store with flourescent lights which caused me to get dizzy (which had become common for me), I left and started to drive home and I started having lightflashes in my peripheral vision like cars were speeding past me but there were no cars, I got off the side of the road and felt like I had some type of seizure, no shaking but my mind got fuzzy, I couldn't orient myself, I couldn't move to call for help, etc (luckily once the flashing lights started I had pulled off the highway and parked). I sat for a good 10 minutes unable to think enough to call for help. I finally was able to hit redial on my cell and call my husband but couldn't tell him where I was or descirbe what was wrong. By a stroke of luck I described what I could see around me and he recognized the colors of signs I was describing and knew where to find me.
After extensive testing and seeing several specialists the ONLY thing that they all could agree on was that I had a bad reaction to the aspartame(I had drank 4 cans back to back that morning with nothing else just prior to this all happening and was popping sugar free gum like it was going out of style. I feel like i was addicted to the aspartame).
I immediately switched to iced tea for my caffeine addiction and have not had any problems since...except when I drink diet soda. I don't know if it's subconcious now or if I really am sensitive to it, I do know that it scared the crud out of me and I will not allow my kids to drink any, and avoid it myself if I can.