The seven essential amino acids are leucine, phenylalanine, lysine, isoleucine, histidine, valine, and tryptophan.
The double-blind, randomised, placebo-controlled trial showed that participants who consumed 6g of these amino acids significantly improved their cognitive function and social interaction than the placebo group, which is expected in preventing cognitive decline.
For a rapidly ageing country like Japan, decline in cognitive function has become a major social issue.
One of the authors and researchers at Ajinomoto’s Research Institute for Bioscience Products & Fine Chemicals, Michihiro Takada, said “Deterioration of cognitive function interferes with daily life, so maintaining and improving cognitive function is important in reducing the burden on society as a whole, such as medical care and long-term care, as well as helping to maintain and improve quality of life.”
“Multiple studies have been reported on proteins as one of the nutrients related to cognitive function, so we focused on the amino acids that make up proteins.”
“We decided to study the effectiveness of seven essential amino acids that can easily reach the brain from the blood and may be related to cognitive function,” Takada said.
Published in the Frontiers in Nutrition, the study was conducted by Ajinomoto and the Tokyo Metropolitan Institute of Gerontology.
A total of 105 participants (55 years or older) were enrolled. Participants were healthy, with no impairment in learning function and not diagnosed with dementia.
Although, they had awareness of forgetfulness or found to have forgetfulness by someone.
Participants were randomly divided into three groups - placebo, 3g and 6g of amino acids.
Ajinomoto formulated the powder specifically for this trial.
For the treatment group, it consisted of a granular powder (1.5g) containing 0.47 g of leucine, 0.42 g of phenylalanine, 0.33 g of lysine hydrochloride, 0.13 g of isoleucine, 0.08 g of histidine hydrochloride, 0.06 g of valine, and 0.01 g of tryptophan.
In the 3g group, subjects took the powder twice a day on an empty stomach.
For the 6g group, subjects took double the dosage, and twice per day.
The placebo group powder was corn starch and lactose.
Each group took the powders for 12 weeks.
Primary outcome was cognition function and secondary outcome was psychosocial functions, assessed at baseline and after week 12.
While there are nine essential amino acids in total, the trial only assessed seven of them.
Takada explained that the neurotransmitters in the brain, which are indispensable for maintaining cognitive function, are made from amino acids.
“The composition (of seven amino acids) is designed with the concept of delivering the optimal amino acid composition to the brain.”
“Leucine, valine, isoleucine and lysine are converted to glutamic acid, phenylalanine is converted to tyrosine, and are involved in synthesis of neurotransmitters dopamine, noradrenaline and adrenaline. These are neurotransmitters that play important roles in learning, memory, attention, executive function, motivation and others.”
“In addition, tryptophan and histidine are also converted into neurotransmitters such as serotonin and histamine in the body, respectively, and play important roles in mental stability and awakening.”
Takada explained the trial did not include threonine and methionine, “we could not confirm enough knowledge about the relationship between cognitive function and the brain function that supports it.”
Attention and working memory
The findings showed that the time taken for participants ingesting 6g of amino acids to finish a task significantly improved by 14.6 seconds compared to the placebo group after 12 weeks (p=0.04).
Researchers wrote: “The faster performance suggests the improvement of the ability to concentrate on the task, pay attention to multiple tasks and memorise information needed for doing tasks, which is related with working memory. These results indicate that daily intake of 6 g of amino acids contributes to improved attention and executive function.”
The difference between the placebo and 3g group was not significant (p=0.94).
For the secondary outcome, scores associated to positive emotion (cheerful, active, fresh) improved as well as social interactions.
The daily intake of seven essential amino acids resulted in improved attention and cognitive flexibility and psychosocial functioning, but the effect required 6g of daily intake.
Of the seven amino acids used in this study, some amino acids such as tryptophan and phenylalanine may have antidepressant-like effects associated with mental health.
Researchers explained that the intake of essential amino acids directly affects brain function through the transfer of amino acids to the brain, in particular, affecting frontal lobe function.
However, “It is not possible to elucidate the mechanism based solely on the results of this study, which aimed to investigate the intervention effect of essential amino acid intake.”
Moreover, it is not clear whether the intervention effect remained after intake is stopped.
As the intervention period was only three months, researchers recommend long-term observational studies in examining whether the efficacy of amino acids impacts the prevention of future cognitive decline.
Source: Frontiers in Nutrition
“Intake of Seven Essential Amino Acids Improves Cognitive Function and Psychological and Social Function in Middle-Aged and Older Adults: A Double-Blind, Randomized, Placebo-Controlled Trial”
Authors: Hiroyuki Suzuki, et al.