If there is an opinion that can possibly be had on something there is going to be someone out there that has written a story about it. Diet soda is frequently a target for these sorts of people and most of the time when I hear these stories it is coming from the type of people that either A) live some sort of super-pure life where their body is a temple or B) they are the type of person that enjoys finding fault in anything that is popular.
There are many things that are said about diet soda and then they don't actually provide the information to back it up. If you dig into the numbers and the studies that these results came from, you can quickly ascertain that there is a really good chance that the connection isn't really there and that it is just as likely to be a coincidence as it is any sort of real connection.
This is the opinion that will be put down there by someone who is either intentionally avoiding the actual conclusions in the studies, or they don't even know about the actual study and just are parroting something they heard someone else say.
The fact of the matter is that Boston University actually DID do a study of 3,000 Americans who have developed dementia and had a stroke to try to find a commonality between them all. The conclusion that someone can come to when an anti-diet beverage person wants to make something sound really bad is this one thing: "Diet soda drinkers nearly tripled the odds of stroke and dementia over those who did not drink it."
There is just one problem with this extrapolation. A lot of people drink diet soda, not very many people have dementia and strokes. Therefore, it could be a mere coincidence that the two seem to be connected.
The head of the research, Dr. Matthew Pase, even goes on the record in the actual study notes to say
Only 81, or 5%, of the people in the study were diagnosed with dementia, and only 97, or 3%, had a stroke.
“At the end of the day, we’re talking about small numbers of people,” says Pase. “I don’t think that people should be alarmed.”
He went on to say that he and his study are not trying to connect the two because there are too many immeasurable factors involved such as the fact that people with deteriorating health may have actually tried to curtail it by changing over to diet sodas after the "wheels of the disease" were already rolling. Basically the head of the study that anti-diet-soda folks are always referring to actually says in the body of the article that there is not connection between diet soda and dementia / stroke... yet people quote his study to attempt to prove the exact opposite.
At the end of the day there is and likely always will be a crusade against things that people don't understand. How is it possible that we can make something taste sweet, without having any sugar or calories in it? It is a bit scary when you think about it because the old rule is that you can't make something out of nothing.
Back in 2005 the world was "shocked" when a study was done on rats and the end result that the researchers came to was that aspartame (an artificial sweetener) was the cause of rats developing many types of cancer. There was a very massive flaw about this study that was pointed out by other researchers and this is why we have "peer reviews" of any study.
The people who reviewed the data said that it was flawed because the rats in question were allowed to die of natural causes rather than be "sacrificed" at a certain age the way that this sort of testing is normally done. Therefore, the rats were generally at a very advanced age when they died and rats, just like humans, have a much higher chance of developing cancers when they are older. There was also no control group (rookie mistake!) to identify the differences in the rats that were fed Aspartame and those that weren't. It's almost as though the researchers began this study with the objective being to demonize Aspartame.
Just like most rumors though, the bad stuff stuck, and the correction / retraction wasn't read by anyone.
This attempted badmouthing if diet sodas goes back decades, even to the 70's and upon peer review, the cases are always thrown out because researchers don't follow the widely-accepted scientific methods in place for this sort of research. You can read one such abstract here if you are interested.
For me, I am willing to take the risk that diet soda's magical ingredient might be playing games inside of my body because I already know that the alternative (drinking regular soda) is FAR MORE harmful.
Would it be better to just drink water all the time? Of course it would be. But that wouldn't be much fun now, would it?