Food is not only essential for our bodily functions, but also for our brain functioning and associated behavioural performance. Some studies have shown that eating more of a certain nutritional compound can enhance your performance. But is it really that simple? Can food supplements support our performance? While performing studies on the micronutrient tyrosine, I found out that it is not that simple, and I will tell you why.

Your food contains a range of nutrients that your body uses amongst others as energy sources and as building blocks for cells. For example, protein-rich food such as dairy, grains and seeds are made up of compounds called amino acids. Amino acids are used for different purposes in your body. Muscles use amino acids from your diet to grow. Some people take advantage of this process to increase muscle growth by eating extra protein in combination with exercise.

But amino acids also have a very important role for brain functioning; specific amino acids such as tryptophan, phenylalanine and tyrosine are precursors for neurotransmitters. Specifically tyrosine is a precursor for the neurotransmitter dopamine, which is crucially involved in cognitive processes such as short-term memory, briefly memorizing a phone number or grocery list. Ingested tyrosine from a bowl of yoghurt or a supplement is digested in your intestines, taken up into the bloodstream and then passes through the barrier between the blood stream and the brain (the blood-brain-barrier). In neurons in the brain, tyrosine is further processed and converted into dopamine. Here, dopamine influences the strength and pattern of neuronal activity and hereby contributes to cognitive performance such as short-term memory.

Short-term memory functions optimally most of the time, but can also be challenged. For example during stressful events like an exam or when faced with many tasks on a busy day, many people experience trouble remembering items. Another example is advancing age; elderly people often experience a decrease in their short-term memory capacity. These decrements in short-term memory have been shown to be caused by suboptimal levels of brain dopamine.

The intriguing idea arises to preserve or restore optimal levels of dopamine in the brain with a pharmacological tweak, or even better, using a freely available nutritional compound. Could it be that simple? Yes and no. Yes, if you eat high amounts of tyrosine, there will be more dopamine precursors going to your brain. But the effects on short-term memory vary between individuals and experiments.

Various experiments have been conducted using tyrosine supplementation to see if cognitive performance can be preserved, with mixed success.

In groups of military personnel, negative effects of stress or sleep deprivation on short-term memory were successfully countered. Subjects were asked to take an ice-cold water bath, known to induce stress, and to perform a short-term memory task [1]. In other experiments subjects remained awake during the night or performed challenging tasks on a computer in a noisy room, mimicking a cockpit [2,3].

The group that took tyrosine before or during these stressful interventions showed less decline in their short-term memory than the group that ingested a placebo compound. Tyrosine supplementation also benefitted performance on a cognitive challenge without a physical stressor, compared with performing a simpler task. Other experiments, without a physical or cognitive stressor didn’t show any differences in performance compared with a control group.

These results show that tyrosine supplementation can benefit performance on cognitive processes, such as short-term memory, but only during challenging or stressful situations that induce a shortage of brain dopamine (for review see 4,5).

However, results have also been shown to vary with age. Experiments in elderly people showed that tyrosine also influences the most challenging task compared with simple processes, but contrary to observations in younger adults, in many older adults tyrosine decreased rather than improved performance [6,7]! It seems that the effects seen in young(er) adults no longer hold in healthy aging adults. This can be due to changes in the dopamine system in the brain with aging, as well as changes in other bodily functions, such as the processing of protein and insulin. This doesn’t mean that tyrosine supplementation should be avoided all together for older adults. The results so far suggest that dosages should be adjusted downwards for the elderly body. Further testing is needed to conclude on the potential of tyrosine to support short-term memory in the elderly.

We can conclude that nutrients affect behavior, but importantly, these effects vary between individuals. So, unfortunately, one size does not fit all. To assure benefits from nutrient supplementation or diet rather than wasteful use or unintended effects, dosages should be carefully checked and circumstances of use should be considered.

REFERENCES
O’Brien, C., Mahoney, C., Tharion, W. J., Sils, I. V., & Castellani, J. W. (2007). Dietary tyrosine benefits cognitive and psychomotor performance during body cooling. Physiology and Behavior, 90(2–3), 301–307

Magill, R., Waters, W., Bray, G., Volaufova, J., Smith, S., Lieberman, H. R., … Ryan, D. (2003). Effects of tyrosine, phentermine, caffeine D-amphetamine, and placebo on cognitive and motor performance deficits during sleep deprivation. Nutritional Neuroscience, 6(4), 237–246.

Deijen, J. B., & Orlebeke, J. F. (1994). Effect of tyrosine on cognitive function and blood pressure under stress. Brain Research Bulletin, 33(3), 319–323.

van de Rest, O., van der Zwaluw, N. L., & de Groot, L. C. P. G. M. (2013). Literature review on the role of dietary protein and amino acids in cognitive functioning and cognitive decline. Amino Acids, 45(5), 1035–1045.

Jongkees, B. J., Hommel, B., Kuhn, S., & Colzato, L. S. (2015). Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands-A review. Journal of Psychiatric Research, 70, 50–57.

Bloemendaal, M., Froböse, M. I., Wegman, J., Zandbelt, B. B., van de Rest, O., Cools, R., & Aarts, E. (2018). Neuro-cognitive effects of acute tyrosine administration on reactive and proactive response inhibition in healthy older adults. ENeuro, 5(2).

van de Rest, O.& Bloemendaal, M., De Heus, R., & Aarts, E. (2017). Dose-dependent effects of oral tyrosine administration on plasma tyrosine levels and cognition in aging. Nutrients, 9(12).

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About Mirjam Bloemendaal, PhD

Mirjam Bloemendaal, PhD is a neuropsychologist by training and obtained a PhD in cognitive neuroimaging by studying cognitive aging using pharmacological and nutritional interventions. She is interested in the effect of physiological processes on mental health and behavioral performance.

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