In Part 1 of this series, we looked at how L-tyrosine affects cognitive performance, mood, and emotion regulation. Today we’ll explore other effects of L-tyrosine, including whether it affects your exercise performance, your ability to regulate your body temperature, and your thyroid function. We’ll end by assessing the best ways to take L-tyrosine, and whether some people should think twice before they try it.
- L-tyrosine might be helpful for exercise done in cold conditions that requires fine-motor skills and/or a lot of cognitive effort.
- If you’re middle aged or older, taking L-tyrosine before cold exposure can improve the function of your blood vessels and hence your ability to maintain your core temperature.
- If you want to try it, take 2 g L-tyrosine on an empty stomach 1 h before whatever you’re using it for.
- If you have hereditary tyrosinaemia, take thyroid medication, take catecholaminergic medication (e.g., MAO (monoamine) oxidase inhibitors), or have chronic migraines, tyrosine supplements probably aren’t for you.
L-tyrosine and exercise performance
L-tyrosine intake supports the synthesis of catecholamines, which are important to many brain functions, including motivation. These chemicals also have effects outside the brain. For example, noradrenaline tends to increase heart rate, blood pressure, and blood glucose, readying the body for mental and physical challenges. Because of these actions, people have been interested in whether L-tyrosine intake affects exercise performance.
In Part 1, I mentioned a systematic review of the effects of tyrosine intake on brain function. The scientists also looked at whether tyrosine affects exercise performance. To do so, they included 6 studies, all of which included small numbers of physically trained young men. Two experiments included cycling time trials (how fast someone can ride a certain distance), 3 looked at cycling time to exhaustion (how long someone can ride at a fixed workload), and 1 tested time to exhaustion running on a treadmill. Notably, 3 of these were done at high temperatures, for extreme temperatures tend to increase demands on catecholamine synthesis, which L-tyrosine can support.
The results showed that while 1 study found tyrosine enhanced cycling time to exhaustion in the heat, 5 found no differences between tyrosine and placebo. The only well-controlled study of the effects of isolated L-tyrosine supplementation on exercise published since this review looked at a brisk 1-h walk followed by an exercise test in which people had to cover 2.4 km as fast as possible while carrying a 25-kg backpack in the heat (sounds like fun!). Again, tyrosine supplementation had no effect on exercise performance, nor did it influence measures of cognition before, during, and after exercise.
While these findings don't show substantial effects of L-tyrosine, it might still be that it can support performance in some types of exercise. As L-tyrosine can protect against cold-induced decreases in shooting accuracy, it could be that L-tyrosine is helpful for exercise done in cold conditions that requires fine-motor skills and a lot of cognitive effort. This brings us to how L-tyrosine intake influences ability to effectively regulate body temperature.
L-tyrosine can support thermoregulation in the cold
As high blood flow to your certain parts of your skin promotes heat loss, to maintain your core temperature in the cold, your body tends to shunt blood away from these regions by narrowing blood vessels near the skin. This mechanism generally works well in young people, but it deteriorates as people age. As noradrenaline is involved in the reflex constriction of blood vessels, scientists in the US have tested whether L-tyrosine can improve this blood flow redistribution. Sure enough, research done a few years ago found that L-tyrosine supplementation improved vasoconstriction in elderly adults exposed to 30 mins of whole-body cooling. There was no effect in young adults. A subsequent study by the same people replicated these findings, showing that L-tyrosine improved vasoconstriction in elderly people exposed to 90 mins of whole-body cooling. But they also discovered that this improved regulation of core body temperature, which can be critically important. This effect was large enough that the elderly participants’ responses were as effective as those of healthy adults in their 20s.
While this hasn’t been studied across the lifespan, it seems that if you’re middle aged or older, supplementing L-tyrosine 1 h or so before you know you’ll get cold might be a smart thing to do.
L-tyrosine can affect thyroid function
So far we’ve largely focused on how L-tyrosine intake can affect us by influencing catecholamines. However, L-tyrosine can be metabolised in other ways too. One of these alternative routes uses L-tyrosine to make a thyroid hormone named T4 (thyroxine). It’s therefore possible that L-tyrosine supplementation could affect thyroid function, and the study of female Antarctic researchers I mentioned in my last post found that, during the summer and winter, L-tyrosine decreased thyroid-stimulating hormone. Once again though, there was a seasonal effect – in the winter only, tyrosine also increased free T3 (unbound triiodothyronine), which is a particularly biologically active thyroid hormone.
There’s clearly a lot more to understand about L-tyrosine supplementation and thyroid function, but results of preliminary research imply that this amino acid can stimulate thyroid function in certain circumstances. This might be either beneficial (in hypothyroid conditions) or detrimental (in hyperthyroid ones), but this is speculative.
L-tyrosine for phenylketonuria
Chances are that you neither have phenylketonuria nor know anybody who does, so feel free to skip this. Phenylketonuria is a genetic disease in which someone cannot properly metabolise the amino acid phenylalanine, which can build to toxic levels. It’s therefore treated by giving patients low-phenylalanine diets, which don’t taste great and need to be started early in life. As phenylalanine is a precursor to tyrosine, people have proposed that some of the brain dysfunction experienced by phenylketonuria patients could be alleviated by L-tyrosine intake. While this hasn’t been well studied, studies of phenylketonuria patients haven’t shown any obvious effects of L-tyrosine intake.
Is L-tyrosine safe, and are there people who should avoid it?
To my knowledge, the study of female Antarctic researchers is about the longest study (13 weeks) of high-dose L-tyrosine supplementation (12 g per day), and these people didn’t experience any ill effects.
As the enzyme (tyrosine hydroxylase) that converts tyrosine to L-DOPA is quite near saturation under normal circumstances, any excess L-tyrosine consumed is bound to not raise L-DOPA much further than physiological levels, so it’s presumably practically impossible to overdose.
Next, many people take L-tyrosine away from consuming other amino acids to maximise tyrosine entry into the brain (if it’s consumed with certain other amino acids, some of it will be crowded out of the transporter that shuttles it into the brain).
Please also bear in mind that many foods are rich in tyrosine - some types of meat and fish contain over 1 g L-tyrosine per 100 g.
All of this suggests that L-tyrosine supplementation is likely very safe for most of us, even if there aren’t many long-term studies on it. Nevertheless, the following groups of people might want to think twice before supplementation:
- People with hereditary tyrosinaemia, a rare genetic disorder that compromises the ability to break down tyrosine.
- People with chronic migraines. Some of these people have abnormally high catecholamine levels in their blood, which plausibly contributes to some of their troubles.
- People with hyperthyroidism and people taking medications for thyroid dysfunction.
- People taking catecholaminergic drugs, including Levodopa, monoamine oxidase inhibitors, and antipsychotics.
One question that always pops up is whether L-tyrosine is safe for breastfeeding women. It seems to be. In breastfeeding women, 2 g, 5 g, or 10 g L-tyrosine increased tyrosine in the women’s plasma but had had no effects on tyrosine in breast milk.
What’s the best way to take L-tyrosine?
Studies of L-tyrosine have used a BIIIIG variety of dosing schedules. At one end of the spectrum, many studies by highly respected scientists use a single dose of 2 g. At the other end, some researchers have given people 20 g per day. It’s also been quite common for scientists to tailor dose to bodyweight. But as far as I can tell, nobody has really systematically tried to optimise tyrosine dose.
Personally, I’d gravitate to taking 2 g on an empty stomach. This is a proven dose, it’s almost certainly enough to saturate the tyrosine hydroxylase enzyme, and it’s about what a lot of us consume at a single dinner. It’s fine to consume this with a small amount of carbohydrate and/or fat, but I’d avoid consuming most other amino acids with it, for some impair tyrosine uptake.
With respect to timing, most studies in which people consume 2 g L-tyrosine have had people take it 1 h before starting a task. This makes sense, for tyrosine levels in the blood usually peak 1 to 2 h after intake and can remain elevated for several hours thereafter.
Regarding the form of tyrosine to take, stick with regular L-tyrosine. Many supposedly “nootropic” supplements contain N-acetyl-L-tyrosine. Put simply, N-acetyl-L-tyrosine just hasn’t been studied for much other than how well it raises tyrosine in the blood (not very) and how it’s excreted (mostly intact, suggesting it doesn't do much). So stick with regular L-tyrosine.
What does L-tyrosine go well with?
Answering this is tricky, for studies haven’t tried to systematically answer this. Instead, a few studies have simply assessed the effects of L-tyrosine in combination with other supplements. Here are some of the more interesting ones:
- A 2007 study found that a supplement containing L-tyrosine, caffeine, capsaicin, and catechins modestly increased how many calories people burn. Over 8 weeks of a weight loss diet, people taking the supplement lost 0.9 kg more weight than those taking a placebo.
- A 2017 study showed that consuming 2 g L-tryptophan, 10 g L-tyrosine, and blueberry juice with blueberry extract prevented depressed mood in postpartum women.
- A 2019 study reported that caffeine, L-theanine, and L-tyrosine improved movement accuracy in university athletes tested using a device that evaluates multiple aspects of mental and physical performance.
L-tyrosine can come in handy in quite a few circumstances. Its best-proven benefit is its ability to enhance brain function when you’re doing something hard (e.g., after working insufficient sleep), but L-tyrosine might also help lift your spirit, improve your fine motor skills, and maintain your body temperature when you’re on the verge of turning blue.