The effects of tyrosine on plasma response and cognition in aging are unknown. We assessed\nthe dose-dependent response to tyrosine administration in older adults in both plasma tyrosine\nconcentrations and working memory performance. In this double blind randomized cross-over\ntrial 17 older adults (aged 60ââ?¬â??75 years) received a single administration of 100, 150, or 200 mg/kg\nbody weight of tyrosine. For comparison, 17 young adults (aged 18ââ?¬â??35 years) received a dose of\n150 mg/kg body weight of tyrosine. Tyrosine plasma concentrations were determined before and\n90, 120, 150, 180, 210, and 240 min after tyrosine intake. Working memory was assessed using the\nN-back task at 90 min after tyrosine administration. Older adults showed a dose-dependent increase\nin plasma tyrosine concentrations (p < 0.001), and the plasma response was higher than for young\nadults with the same dose (p < 0.001). Load-dependent working memory performance decreased with\nhigher doses of tyrosine (p = 0.048), especially in older adults with greater dose-dependent plasma\ntyrosine responses (p = 0.035). Our results show an age-related increase in plasma tyrosine response,\nwhich was associated with a dose-dependent decline in cognitive functioning in older adults
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