Amino acids are the building blocks of protein. Protein consists of long chains of amino acids and there are 20 different types of amino acids. Some are essential (meaning our body doesn’t produce them itself) and some are classed as non-essential, (1).
Neurotransmitters are chemical messengers within the body such as serotonin, GABA, dopamine, acetylcholine, endorphins and adrenaline. Their job is to transmit signals around the body via muscles, glands and nerves. They are part of the nervous system and play a crucial role in our development and many bodily functions, (2).
There are certain amino acids that have been shown to have an effect on the levels of specific neurotransmitters, which may in turn have the potential to help with the symptoms of ADHD. For example, glycine, L-theanine, L-tyrosine, taurine, acetyl-L-carnitine, GABA, 5-HTP, and L-methionine (SAMe), may be considered as complementary to ADHD interventions, (2).
Acetyl-L-carnitine (ALC), is an amino acid derivative. One study reported that supplementation with ALC significantly reduced symptoms of ADHD, such as hyperactivity and social behaviour in a trial of 51 children aged 6–13). This may be due to ALC stimulating the release of dopamine in various brain regions, (3).
L-Theanine is an amino acid found in both green and black teas and there is a component within it called n-ethylglutamic acid that may have positive calming central nervous system effects. It has the ability to cross the blood-brain barrier, helping to regulate dopamine and serotonin to create a calming effect on the mind, (3).
By enhancing the production of dopamine and serotonin, L-Theanine may also play a role in the formation of GABA which is another neurotransmitter that acts like a “brake” during times of stress. These processes combined help to improve mental, emotional and physical disturbances resulting from being overly stressed, which can result in the emotional dysregulation that often comes with having ADHD. L-theanine also converts to serotonin, which helps to make melatonin, which helps with sleep and relaxation, (4).
To summarise these pathways, L-Theanine, increases concentrations of serotonin and dopamine, as well as GABA. And it also indirectly helps to make melatonin because it makes serotonin which helps to make melatonin. It also increases alpha activity in the brain which is the calming state we reach once we have completed a task, for example, (5).
But what is GABA? Gamma aminobutyric acid (GABA) is a naturally occurring amino acid that acts as a neurotransmitter in your brain. GABA works by blocking certain brain signals and decreasing activity in your nervous system. It does this by attaching to GABA receptors in your brain to produce a calming effect, which can help with feelings of anxiety, stress, and fear. It isn’t available from many food sources other than fermented ones, such as kimchi, miso, and tempeh, which may explain why some probiotics make people ‘feel’ mentally better, (6). So, GABA in combination with L-theanine may help to balance our nervous system, enabling a good night’s deep sleep, and supporting optimal health. L-Theanine not only increases levels of GABA, serotonin, and dopamine, but the opposite to this is glutamate which is an antagonist and the opposite to these calming properties, (6).
Serotonin and 5-HTP
5-HTP is a naturally occurring amino acid produced from the essential amino acid L-tryptophan, which also helps to make serotonin. 5-HTP is the precursor for some neurotransmitters which include serotonin and melatonin. So L-tryptophan (which can be found naturally in foods) converts to 5-HTP which can then help to make serotonin and melatonin, (7). Serotonin, which is also known as 5-HT, may improve mood and promote feelings of wellbeing. It may also impact appetite, sleep cycles and pain perception. Serotonin is mainly produced naturally on the cells of the gut as well as in the part of your brain stem called the Raphe nuclei. Consuming foods high in L-tryptophan may help to boost production of serotonin, which can also help play a role in digestion and the immune system, as well as our mood, (8).
Dopamine is made in the base of our brains through a two-step process. The amino acid tyrosine is first turned into L-dopa, which is then made into dopamine. Dopamine is known as the pleasure neurotransmitter because it is responsible for making us feel good and it activates the reward system in our brains. It also helps us to focus and to learn new information, (8).
It also helps to play a role in muscle movement, the management of heart rate, lactation, pain, sleep and kidneys and blood vessel function,(8).
Your body needs several vitamins and minerals to create dopamine, including iron, niacin (B3), folate, and vitamin B6. If there is a deficiency in one or more of these nutrients, you may have trouble making enough dopamine to meet your body’s needs, (8), so in the case of ADHD it may be worthwhile starting by ensuring your nutrient status is optimal, and then focus on which amino acids you can increase naturally from foods.