ID 1930 -
Tyrozyna
PL: Tyrozyna
EN: L-Tyrosine
Pdf: L-tyrosine
1. Charakterystyka żywności / składnika
The food constituent that is the subject of the health claims is L-tyrosine.
L-Tyrosine is a conditionally indispensable amino acid which occurs naturally in foods, mainly as part of proteins. Dietary L-tyrosine is provided by mixed dietary protein intakes from different sources; it can also be consumed in the form of food supplements. The content of L-tyrosine in foods can be measured by established methods.
The Panel considers that the food constituent, L-tyrosine, is sufficiently characterised.
2.2. Zwiększenie uwagi (ID 440, 1672, 1930)
The claimed effects are “involved in energy production”, “helps to support cognitive performance during exposure to environmentally adverse conditions”, and “cognitive function/mental health”. The Panel assumes that the target population is the general population.
In the context of the proposed wordings and clarifications provided by Member States, the Panel assumes that the claimed effects refer to increased attention (concentration), which is a well defined construct and which can be measured by validated psychometric tests.
The Panel considers that increased attention is a beneficial physiological effect.
3.2. Zwiększenie uwagi (ID 440, 1672, 1930)
The references provided for the scientific substantiation of the claim included textbooks, a publication from an authoritative body, a popular science book and narrative reviews, which mostly reported on tyrosine as a treatment for depression, and on tyrosine toxicity, and did not provide original data for the scientific substantiation of the claimed effect. Some human studies reported on trials in patients groups with narcolepsy/catalepsy, major depression, attention-hyperactivity disorder and phenylketonuria. The Panel considers that the evidence provided does not establish that results obtained in studies on subjects with these disorders can be extrapolated to the general population with regard to attention. Other references were a human study which did not consider a relevant endpoint (but rather covered the rate of tyrosine metabolism) and in vitro/ex vivo studies reporting on aspects (e.g. the properties of the precursor pathway, and the purification and properties of tyrosine transaminase) unrelated to the claimed effect. The Panel considers that no conclusions can be drawn from these references for the scientific substantiation of the claim.
In a double-blind, placebo-controlled study (Deijen and Orlebeke, 1994), the effect of a combination of tyrosine (100 mg/kg body weight) and vitamin B6 (10 mg) on cognitive function was investigated in 16 healthy young male and female subjects under stress conditions (90 dB noise). The Panel considers that no conclusions can be drawn from a study using a combination of tyrosine and vitamin B6 on the effect of L-tyrosine alone.
Three human intervention studies (Banderet and Lieberman, 1989; Neri et al., 1995; Thomas et al., 1999) investigated the effects of L-tyrosine ingestion on cognitive function under various levels of stress conditions.
In the double-blind placebo-controlled study by Banderet and Liebermann (1989), 23 males (18- 20 years) underwent two stressor conditions (15°C/4200 m altitude pressure and 15°C/4700 m altitude pressure) and a control condition (22°C/550 m altitude) after ingesting either tyrosine (2 doses of 50 mg/kg body weight) or placebo (not described). Stressors and control condition were applied for 4.5 hours each with a minimum of 48 hours between sessions. Test sessions started at 7.00 am and the treatment was provided at 7.20 am and 8.00 am. Behavioural testing, which started 1 h 20 min after tyrosine/placebo ingestions, included a range of cognitive tests assessing vigilance (choice reaction time task) and attention (sustained attention task, dual vigilance task) along with multiple other endpoints. Analysis was restricted to participants who showed an effect of the stressor (i.e. if differences in scores under stressor conditions and placebo condition were greater than group mean difference). However, no information was available on the number of participants who entered the analysis. The Panel notes that the placebo was not described and that insufficient information was available on the statistical analyses performed. The Panel considers that no conclusions can be drawn from this reference for the scientific substantiation of the claim.
In the randomised, double-blind, placebo-controlled, parallel study by Neri et al. (1995), the effect of tyrosine was assessed in 20 male subjects during an episode of continuous night time work (13 h test duration during the night, from 19.30 pm to 8.20 am). Subjects were submitted to nine experimental blocks of 90 min, separated by 40 min breaks during which they were provided with caffeine-free snacks (composition not described). At 1.30 am and 3.00 am, tyrosine (2 doses of 75 mg/kg body weight, n=10) or placebo (corn starch, 2 doses of 75 mg/kg body weight, n=10) were provided with approximately 113 g of banana yogurt. The testing consisted of a selective attention task (dichotic listening) along with other cognitive endpoints. As an additional stressor, subjects were exposed to a low-frequency 70 dB noise during the tests. Performance on all tasks deteriorated steadily through the night. Differences between groups were not statistically significant for the dichotic listening task. The Panel notes that this study does not show an effect of the consumption of L-tyrosine on attention endpoints.
In a cross-over, double-blind study, Thomas et al. (1999) administered, in a random order, L-crystalline tyrosine (150 mg/kg body weight) and placebo (7 g microcrystalline cellulose) with 70 g apple sauce to 20 young healthy male and female subjects (age range 20-38 years) to investigate the effects of tyrosine ingestion on performance under mild stress conditions. Cognitive testing began 60 minutes post-ingestion and was administered either in a multi-tasking environment (mild stress condition) or in a simple task environment. In the multi-tasking environment subjects were required to simultaneously perform a Sternberg Memory Task (working memory task), an arithmetic task (addition of numbers), a visual monitoring task and an auditory monitoring task (both sustained attention tasks). In the simple task environment, participants were given the Sternberg task and the visual monitoring task only. Differences between groups were not statistically significant for the visual monitoring task and the auditory monitoring task. The Panel notes that this study does not show an effect of the consumption of L-tyrosine on attention endpoints.
In weighing the evidence, the Panel took into account that the two studies from which conclusions could be drawn for the scientific substantiation of the claim showed no effects of L-tyrosine, compared to placebo on attention endpoints.
The Panel concludes that a cause and effect relationship has not been established between the consumption of L-tyrosine and increased attention.
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