The American National Institute of Health did a study of hundreds of thousands of Americans and then followed them for years. What they found was that the frequent consumption of sweetened beverages, especially diet drinks, may increase depression risk among older adults. Whether soda, fruit-flavoured drinks, or iced tea, those artificially sweetened drinks appeared to carry higher risk. There was a benefit in coffee drinkers compared to non-drinkers, but if they added sugar, much of the benefits appeared to disappear, and if they added Equal or Sweet-and-Low, the risk appeared to go up.
Those with a history of depression might be especially vulnerable, researches concluded. Researchers at Case Western designed a study to ascertain whether individuals with mood disorders are particularly vulnerable to adverse effects of aspartame. Although they had planned on recruiting 40 patients with depression and 40 controls, the project was halted early by the Institutional Review Board for safety reasons because of the severity of reactions to aspartame within the group of patients with a history of depression.