The Effects of L-Tryptophan Supplementation on Mood, Sleep Quality and Cognitive function: a Randomised Double-Blind Placebo-Controlled Trial.
Background: The essential amino acid L-tryptophan is the precursor molecule to the monoamine neurotransmitter serotonin and the hormone melatonin. Within the central nervous system, both of these compounds play a major role in the regulation of mood, circadian rhythm, memory, learning and cognition. The scientific literature has shown that decreased serotonergic activity correlates with affective disorders, such as major depression. An abundance of studies have shown that such a state can be induced, in some humans and in animal models, through the elimination of dietary tryptophan. Conversely, the effects of tryptophan supplementation have not been studied in as much depth. Much of the current literature in this area has increased tryptophan intake through the use of dietary intervention and has generally enrolled exclusively older-aged participants. Many of the current studies have shown that an increase in dietary tryptophan can improve mood, however many of these studies have major limitations, such as short interventions and poor study design. Aims: Determine whether supplementing young adults with a daily dose of L-tryptophan has any statistically significant effects on markers of mood, sleep quality and cognitive function. Methodology: In this double-blind placebo-controlled randomised trial, participants (n=8) aged 18-35 were randomised to receive either 1,200mg L-tryptophan (n=3) or placebo (n=5) daily for 14 days, following a parallel study design. Measures of mood (abbreviated profile of mood states), sleep quality (Pittsburgh sleep quality index) and cognitive function (stroop colour interference test and digit span test) were taken from each participant, once at baseline and once at endpoint. Participant protein intake was quantified through the use of a diet diary, filled out during the course of the trial. Results: Post-intervention, participants receiving L-tryptophan were observed to have had an increased total completion time when carrying out the digit span test (p = 0.01). Additionally, between baseline and endpoint, levels tension were seen to rise in the control group (p = 0.01). There were no statistically significant changes in any of the other markers of mood, sleep quality and cognitive function (p > 0.05), in either group. A Pearson’s correlation found no significant relationship between protein intake and digit span scores (r = 0.95, p = 0.16). Conclusion: These findings may indicate that L-tryptophan supplementation does not improve markers of mood, sleep quality and cognitive function in young adults. However, this study had multiple limitations, such as small sample size, large drop-out rate, insufficient dietary analysis and lack of biochemical tests. Keywords: L-tryptophan, serotonin, monoamine, mood, cognition, sleep