“We found that people who drank at least one can of diet soda each day had a 3 times increased risk of stroke and dementia than those not drinking any such beverages.”
Source: Do Diet Sodas Pose Health Risks?
Observational study and the researchers are quick to note the study findings do not prove cause and effect. There also may be an element of reverse causality.
I personally do not drink any sugar or artificially sweetened soft drinks.
I do drink a ton of coffee.