Abstract
The effects of tyrosine on plasma response and cognition in aging are unknown. We assessed the dose-dependent response to tyrosine administration in older adults in both plasma tyrosine concentrations and working memory performance. In this double blind randomized cross-over trial 17 older adults (aged 60–75 years) received a single administration of 100, 150, or 200 mg/kg body weight of tyrosine. For comparison, 17 young adults (aged 18–35 years) received a dose of 150 mg/kg body weight of tyrosine. Tyrosine plasma concentrations were determined before and 90, 120, 150, 180, 210, and 240 min after tyrosine intake. Working memory was assessed using the N-back task at 90 min after tyrosine administration. Older adults showed a dose-dependent increase in plasma tyrosine concentrations (p < 0.001), and the plasma response was higher than for young adults with the same dose (p < 0.001). Load-dependent working memory performance decreased with higher doses of tyrosine (p = 0.048), especially in older adults with greater dose-dependent plasma tyrosine responses (p = 0.035). Our results show an age-related increase in plasma tyrosine response, which was associated with a dose-dependent decline in cognitive functioning in older adults.
Highlights
IntroductionTyrosine is one of the conditionally essential amino acids and is found in protein-rich foods such as dairy, meat, fish, eggs, seeds, nuts, and beans
Tyrosine is one of the conditionally essential amino acids and is found in protein-rich foods such as dairy, meat, fish, eggs, seeds, nuts, and beans. It can be synthesized from the essential amino acid phenylalanine, but this is dependent on sufficient availability of this precursor [1]
Future placebo-controlled designs should further test the beneficial or unfavorable effects of tyrosine administration on cognitive functioning in older adults, including lower doses
Summary
Tyrosine is one of the conditionally essential amino acids and is found in protein-rich foods such as dairy, meat, fish, eggs, seeds, nuts, and beans. Studies of tyrosine supplementation in young adults showed that after doses of 100 mg/kg body weight and 150 mg/kg body weight, peak plasma concentrations of the compound were reached approximately two hours after ingestion. Changes in peripheral tyrosine absorption and metabolism, for example in liver [3], muscles [4], and melanocytes [5], may occur and, the same dose of tyrosine may lead to a different response in plasma (i.e., peripheral) tyrosine concentrations in older relative to young. We aimed to investigate this in older adults with three tyrosine doses using a randomized cross-over design (100 mg/kg, 150 mg/kg, and 200 mg/kg body weight of tyrosine) and a 150 mg/kg body weight dose of tyrosine in young adults for comparison
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