Experts are questioning whether diet drinks could raise depression risk, after a large study has found a link.
Research in the United States on more than 250,000 people found depression was more common among frequent consumers of artificially sweetened beverages.
The work, which will be presented at the American Academy of Neurology's annual meeting, did not look at the cause for this link.
Drinking coffee was linked with a lower risk of depression. People who drank four cups a day were 10% less likely to be diagnosed with depression during the 10-year study period than those who drank no coffee.
But those who drank four cans or glasses of diet fizzy drinks or artificially sweetened juice a day increased their risk of depression by about a third.
Dr Honglei Chen of the National Institutes of Health in North Carolina, said more studies were needed to explore this.