The Benefits of L-Tyrosine for Athletes: The Evidence Base

L-tyrosine often appears in pre-workout complexes with promises of "focus," "energy" and "endurance." Do these promises have any basis? Our editorial team analyzed the key studies of tyrosine in physically active people and under stress in order to separate real results from marketing.

Why tyrosine interests athletes

The theoretical basis for using tyrosine in sport is the role of catecholamines in physical and mental work. Dopamine and noradrenaline affect motivation, attention, the perception of effort and thermoregulation. During prolonged or grueling exertion, especially in the heat, the neurotransmitter balance in the brain changes, and this is regarded as one of the mechanisms of so-called central fatigue.

The hypothesis is that additional tyrosine can support catecholamine synthesis in situations where they are used up the most. Biochemically this is justified: in a state of intense neuronal activity, the rate-limiting enzyme tyrosine hydroxylase becomes more sensitive to substrate availability (Fernstrom, Fernstrom, 2007).

The second reason for interest is the cognitive component of sport. In team games, combat sports, shooting or motorsport, decisions are made under fatigue and stress. If tyrosine helps maintain working memory under load, this is potentially useful for athletes too.

Finally, tyrosine is an ordinary dietary amino acid with good tolerability at research doses. For athletes it is also important that it is not on the WADA Prohibited List. So interest in it is understandable, but the question is how well the theory is confirmed in practice.

Endurance and training in the heat

The most interesting results for sport were obtained in studies of endurance in warm conditions. It is there that the central fatigue hypothesis looks most convincing.

So the picture is contradictory. The study by Tumilty et al. (2011) showed a statistically significant increase in time to exhaustion in the heat, which became an argument for tyrosine's proponents. However, an almost identical study in design by Watson et al. (2012) did not reproduce this effect.

In moderate temperature conditions the data are even less optimistic. Chinevere et al. (2002) found no advantage from adding tyrosine to a carbohydrate drink during prolonged cycling. That is, in ordinary endurance training conditions tyrosine most likely gives no noticeable advantage.

Both studies in the heat were small, with a few participants, and were conducted on well-trained men. Generalizing them to women, amateurs or other types of exertion is incorrect. Larger studies are needed for a definitive conclusion.

As for strength training and maximal strength, our editorial team is not aware of convincing studies that would show a benefit of tyrosine. The promises of "more reps" in the advertising of pre-workout complexes are not supported by reliable data.

Cognitive function under stress

A much more convincing evidence base concerns cognitive function under stress. The review by Jongkees et al. (2015) concluded that tyrosine most likely helps maintain cognitive productivity when the demands on neurotransmitter systems are high, and has almost no effect in a calm state.

• Cold and hypoxia.In the study by Banderet and Lieberman (1989), tyrosine reduced the deterioration of mood and cognitive measures in cold and under conditions that simulated altitude.
• Military training.In cadets after a week of an intensive combat training course, tyrosine was associated with better memory measures (Deijen et al., 1999).
• Working memory.Colzato et al. (2013) showed that tyrosine improved the updating of information in working memory during a difficult N-back task.

These results have some significance for athletes: in team sports, during multi-day competitions, in the mountains or in cold, cognitive exhaustion can affect the result no less than physical exhaustion. However, there are almost no direct studies in sports competitions.

It should also be remembered that tyrosine's effect is rather "less deterioration" in difficult conditions, not improvement above the norm. A person who has slept well and is not under stress will hardly feel a noticeable difference.

Strengths and weaknesses of the evidence base

In assessing tyrosine studies, our editorial team highlights several aspects that are important to consider before drawing conclusions for yourself.

Strengths.There is a clear biochemical mechanism. The results of cognitive studies under stress were reproduced in various groups - from the military to students. Most studies had a double-blind placebo-controlled design, and tyrosine at research doses was generally well tolerated.

Weaknesses.The samples in most studies are small. The protocols are very different - from single doses to multi-day courses. The results regarding physical endurance are contradictory. There are also few studies in women and older people.

Another problem is transferring laboratory conditions to real life. Cycling to exhaustion in a climate chamber differs from a marathon, a football match or a multi-hour tournament. So even positive results require careful interpretation.

Finally, most studies used high doses calculated for body weight - about 100-150 mg/kg. Typical servings in supplements are often much smaller, so obtaining the effect described in the literature from a single capsule is unlikely. We write about the practical side of dosing separately.

Who tyrosine may be useful for

Given the available data, our editorial team highlights situations in which tyrosine makes the most sense and situations where a benefit from it should not be expected.

For athletes in technical and team sports, tyrosine may be an option for very intense days, for example during tournaments with several games in a row or after flights. However, it is worth experimenting in training rather than during major competitions.

For people who simply want "more energy" for an ordinary workout, our editorial team advises first reviewing sleep, nutrition and recovery. These factors have a much stronger effect than any amino acid.

Before starting, people with hyperthyroidism, those taking MAO inhibitors, levothyroxine or levodopa need to consult a doctor. More on this - in the article on tyrosine's side effects.

Editorial conclusions

The most convincing data for tyrosine concern the preservation of cognitive function - working memory and attention - under stress: cold, hypoxia, sleep deprivation, intensive training.

Regarding physical endurance the data are contradictory: one study in the heat showed a benefit, another did not, and in moderate conditions no effect was found. There is no evidence of a benefit for strength and muscle mass.

So tyrosine is a niche tool for specific stressful situations, not a universal sports supplement.

We also recommend the materials "L-Tyrosine: What It Is and How It Works," "How to Take L-Tyrosine: Dosage, Timing, Duration" and "Side Effects of L-Tyrosine."

References

1. Jongkees BJ, Hommel B, Kühn S, Colzato LS. Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands — a review. J Psychiatr Res. 2015;70:50–57.
2. Tumilty L, Davison G, Beckmann M, Thatcher R. Oral tyrosine supplementation improves exercise capacity in the heat. Eur J Appl Physiol. 2011;111(12):2941–2950.
3. Watson P, Enever S, Page A, et al. Tyrosine supplementation does not influence the capacity to perform prolonged exercise in a warm environment. Int J Sport Nutr Exerc Metab. 2012;22(5):363–373.
4. Chinevere TD, Sawyer RD, Creer AR, et al. Effects of L-tyrosine and carbohydrate ingestion on endurance exercise performance. J Appl Physiol. 2002;93(5):1590–1597.
5. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull. 1989;22(4):759–762.
6. Deijen JB, Wientjes CJ, Vullinghs HF, et al. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Res Bull. 1999;48(2):203–209.
7. Colzato LS, Jongkees BJ, Sellaro R, Hommel B. Working memory reloaded: tyrosine repletes updating in the N-back task. Front Behav Neurosci. 2013;7:200.
8. Fernstrom JD, Fernstrom MH. Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. J Nutr. 2007;137(6 Suppl 1):1539S–1547S.