I saw this article copied in our Sunday paper.
http://www.iht.com/articles/2008/02/06/healthscience/05symp.php
“Researchers have found a correlation between drinking diet soda and metabolic syndrome the collection of risk factors for cardiovascular disease and diabetes that include abdominal obesity, high cholesterol and blood glucose levels and elevated blood pressure.”
Of course if the researchers depended on self-reporting, that opens up a whole new can of worms. They need to do some testing under controlled conditions.
Correlation is not causation. The people with metabolic syndrome may well have selected diet soda AFTER they had a problem as a means to avoid making it worse.