Changes in plasma amino acid and subjective sleepiness ratings in humans after consumingL-tryptophan/maltodextrin mixes.

In animals, there is some evidence that increasing brain tryptophan (TRP) levels can increase brain serotonin (5-HT) synthesis and facilitate sleep onset. The plasma ratio of TRP to the other large neutral amino acids (TRP/LNAA ratio) must at least triple before detectable increases in brain 5-HT occur. In young men, consumption of 500 mg TRP combined with a carbohydrate (CHO) load will triple this ratio. In a study on 72 volunteers with mild insomnia, using subjective ratings of sleep onset and quality, this combination significantly decreased sleep latency. We noticed, however, that young women seemed to be particularly responsive to the sleepiness-inducing effects of TRP/CHO mixes. The present study was designed to examine more closely the effects of TRP/CHO mixes on subjectively rated sedation in young women and to check if their plasma amino acid response differs from that of men. On three evenings, nine healthy young women consumed 0, 500, or 1000 mg TRP combined with 30 g of maltodextrin. Blood samples were collected at 0, 30, 60, 90 and 120 minutes. Sleepiness was rated during the evening. The study was carried out double-blind, and each woman received all 3 treatments balanced across days. Plasma TRP/LNAA ratios tripled after 500 mg and quadrupled after 1000 mg of TRP. All women reported a marked increase in sleepiness with TRP. We conclude that young women do seem to be more sensitive than men to the sedating effect of TRP/CHO mixes but their plasma amino acid responses are similar.