NAC - arthritis

A friend told me that she started experiencing joint pain a few months after starting NAC. It got my attention because it's hard not to notice on this site that a number of people take NAC and have RA or OA. Of course this could be just correlation, not causation. But I have been taking 600 mg for a few months as well and I too am experiencing some joint pain. Of course it could just be because I am 69 and I am exercising hard every day and for over one hour, so of course, there could be simple wear and but I keep wondering to the point that I decided to stop NAC and see where it goes. I wonder if anyone has been experiencing something similar.
Best wishes of great health to all of us!