Reanalysis of Tryptophan Study “Raises Doubts” about Depression Connection

The reanalysis finds that the data supports the null finding—that tryptophan (a proxy for serotonin) is not related to depression.


In a new study, researcher Martin Plöderl calls into question the conclusions of a meta-analysis of tryptophan levels in depression. That study’s conclusions were that tryptophan (a proxy for serotonin) was lower in those with depression. But using a more rigorous statistical method, Plöderl concluded that this was not actually the case. He argues that the original results may have been skewed by false positives from small preliminary studies, since a much larger and more powerful study found that tryptophan levels are unrelated to depression.

“If the one very large study is the most reliable,” Plöderl writes, “then this would be compatible with a zero difference in L-tryptophan level in depressed versus non-depressed people. Similarly, after correction for publication bias, the overall effect is also compatible with a null effect.”

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