"Because depression is such a common problem, finding effective and widely available ways to prevent depression at a population level is an important goal," said study co-author Ed Watkins.

He's a professor of experimental and applied clinical psychology at the University of Exeter in England.
"Diet and nutrition held promise as one means to reach large numbers of people. However, this trial convincingly demonstrates that nutritional supplements do not help to prevent depression," he said in a university news release.