I've never been afraid of aspartame (or other sweeteners) because of cancer risk.  Unlike saccharin, aspartame can cause changes in your mood.  It affects your brain chemistry.  I gave it up after a feeling strange pressure in my head and dizziness led me to read up on it.  Oh, and there's nothing "natural" about aspartame.  From a couple of food techs at General Foods my ex and I knew, it's "chemicals mixed in a vat".