Every year at Thanksgiving, many of us stuff ourselves with turkey, gravy, and pumpkin pie (with whipped cream on top, please). You may have heard that eating turkey makes you feel sleepy. This myth stems from the fact that turkey contains the amino acid tryptophan, which gets converted into the well-known sleep-inducing hormones serotonin and melatonin. However, contrary to popular belief, turkey is not that high in tryptophan compared to any other meal you may eat. Yet, this myth is widespread and well known.
Something you might not know is that tryptophan may actually improve cognition. A study exploring the effects of tryptophan on cognition found that high levels of tryptophan improved memory performance (Booij et al., 2006). Participants completed a battery of cognitive tasks, which included variants of our Double Trouble and Spatial Planning tasks, after consuming a tryptophan-rich supplement. The researchers found that memory performance, more specifically, recognition and speed of retrieval for short- and long-term abstract visual items, was significantly improved.
This relationship is particularly relevant in patients who suffer from depression, whose brains tend to have lower serotonin levels. Turkey aside, that makes it all the more important to measure both cognition and depressive symptoms when treating mental health.
High levels of tryptophan may also improve sustained attention, which is the ability to direct and focus attention to a task over a long period of time (Luciana et al., 2001). Using a letter cancellation task to measure immediate attention and vigilance, participants were instructed to cross out all occurrences of the letters ‘E’ and ‘C’ on a piece of paper with printed capitalized letters. Following a tryptophan rich supplement, participants made fewer errors of omission on the task, suggesting that tryptophan may improve attention and vigilance. However, other tasks reveal lower performance when tryptophan is high, so it is by no means a miracle supplement.
Happy Thanksgiving to you and yours from all of us here at Cambridge Brain Sciences!