Evening dietary tryptophan improves post-sleep behavioral and brain measures of memory function in healthy subjects

Brain serotonin function has been implicated in the control of sleep and sleep related memory dysfunctions are attributed to deficient brain serotonin activity. Depletion of the serotonin precuisor tryptophan reduces brain serotonin function and is found to cause sleep abnormalities and cognitive decline We hypothesized that enhancing pre-sleep brain tryptophan availability via a dietary increase in the ratio of plasma tryptophan to the sum of the other large neutral amino acids (Trpl/LNAA) improves post-sleep memory functioning particularly in subjects with mild sleep complaints. To test whether evening intake of a tryptophan-rich diet increases the plasma Trp/LNAA ratio before sleep and improves early morning behavioral and brain measures of memory function in subjects with mild sleep complaints and control. Twenty-eight subjects with mild sleep complaints and 28 control participated in a double-blind placebo-controlled study. They stayed at the laboratory for an overnight sleep to monitor their post-sleep memory performance following either an evening diet containing tryptophan-rich protein or placebo protein. Evening dietary-induced changes in the plasma Trp/LNAA ratio were measured Besides measuring behavioral changes, also task-related electroencephalographic brain activity (ERP) was measured as an index of cerebral changes in memory function. The tryptophan-rich diet caused a 130% increase in the plasma Trp/LNAA ratio (P= 0.0001) and in all subjects improved behavioral(P=0.001) and ERP (P=0.05) brain measures of memory function. Post-sleep memory function improves after pre-sleep dietary increases in plasma TRP/LNAA probably by improved sleep.