Study: Effect of matcha green tea on cognitive functions and sleep quality in older adults with cognitive decline: A randomized controlled study over 12 months. Image Credit: masa44 / Shutterstock
Daily matcha intake sharpens social cognition and enhances sleep quality, offering potential benefits for older adults facing early stages of cognitive decline.
A randomized controlled clinical trial has recently been conducted to investigate the effect of matcha green tea intake on cognitive function and sleep quality in individuals with mild cognitive impairment. The trial report is published in the journal PLOS ONE.
Background
Dementia is one of the most severe age-related neurodegenerative diseases worldwide. According to the World Alzheimer Report 2022, the number of dementia patients is expected to increase from 57 million in 2019 to 152 million in 2050.
Sleep disturbance is another major problem in aging populations. A reduction in sleep duration from 7 hours to 6 hours has been found to increase dementia risk by 30% in older adults aged 50 – 60 years.
Lifestyle habits, including diet, play a vital role in maintaining cognitive functions in older adults. Preclinical trials have reported that nutrition is essential in preventing dementia-related cognitive decline.
Matcha green tea powder contains several bioactive compounds, including epigallocatechin gallate (EGCG), theanine, and caffeine, which are known to have a beneficial impact on cognitive functions and mood.
In this randomized controlled clinical trial, scientists have investigated the effect of matcha green tea on cognitive function and sleep quality in older adults residing in Japan over a 12-month period.
Study design
A total of 99 older adults aged 60 – 85 years were enrolled for the trial. Of them, 64 had subjective cognitive decline, and 35 had mild cognitive impairment.
The participants were randomly divided into two groups: the intervention group and the control group. The intervention group received two grams of matcha green tea daily for 12 months. The control group participants received placebo capsules that were identical in appearance, color, and odor to the matcha capsules.
Cognitive functions and sleep quality of the participants were measured at baseline and during 3-, 6-, 9-, and 12-month follow-up visits.
Important observations
The study found 98-99% intake rates of matcha and placebo capsules during the entire study period. A significantly increased blood level of theanine in the matcha group compared to that in the placebo group also indicated high adherence to the study intervention.
The evaluation of the perception of facial expressions in cognitive functions indicated that matcha green tea intake is associated with a significant increase in social cognition, including recognition of facial expressions and descriptions (word meanings). However, it is important to note that no significant improvements were observed in the primary cognitive outcomes, including the Montreal Cognitive Assessment (MoCA-J) and Alzheimer's Disease Cooperative Study Activity of Daily Living (ADCS-MCI-ADL) scores. An improving trend in sleep quality was also observed in participants who consumed matcha green tea for 12 months.
However, no significant differences in other tested cognitive functions, including daily-life functional abilities, attention and concentration, executive functions, memory, language, visuoconstructional skills, conceptual thinking, calculations, and orientation, were observed between the matcha and placebo groups.
In the perception of facial expression test, a reduction in false response and a shortening of simple reaction time were observed among matcha-consuming participants compared to placebo-consuming participants.
The study found significant positive correlations between social cognition and cognitive impairment scores in all participants at baseline and 12-month visits. The correlations were stronger among participants with subjective cognitive decline than those with mild cognitive impairment.
Significant correlations were also observed between social cognition scores and conventional cognitive functioning test scores among participants with subjective cognitive decline but not among participants with mild cognitive impairment.
Study significance
The trial findings indicate that regular consumption of matcha green tea can improve emotional perception and sleep quality in older adults with subjective cognitive decline or mild cognitive impairment. However, the absence of significant changes in primary cognitive outcomes suggests that matcha's benefits may be limited to specific aspects of cognition, such as social acuity, rather than broader cognitive functions.
Sleep quality-improving effect of matcha green tea could be attributed to its theanine content. Previous studies involving healthy adults as well as schizophrenia patients have shown that theanine intake is associated with enhanced sleep quality.
A large body of evidence has suggested that sleep disturbance can significantly increase the risk of developing mild cognitive impairment. Improvement in sleep quality through continuous positive airway pressure therapy, together with donepezil administration, has been found to enhance cognitive performance in patients with mild cognitive impairment.
Considering these observations, the current trial suggests that matcha-mediated improvement in sleep quality could be responsible for the observed enhancement in social cognition in the intervention group.
However, the study's findings should be interpreted with caution due to certain limitations. One significant limitation is the relatively small sample size, which may not fully represent the broader population of older adults with cognitive decline. Additionally, the study relied on self-reported sleep quality measures, such as the Pittsburgh Sleep Quality Index (PSQI), which may not capture all aspects of sleep architecture. More objective measures, such as polysomnography, are recommended in future studies to assess sleep stages, including REM and non-REM sleep.
Matcha green tea's cultivation method differs from conventional green tea's. This alternative cultivation method increases the content of catechins and theanine, making matcha green tea potentially superior to green tea in terms of health benefits.
Matcha green tea is widely available and culturally well-accepted worldwide. Thus, incorporating it into the daily routine may offer a simple yet effective strategy for cognitive enhancement, sleep quality improvement, and dementia prevention.
Future studies are needed to explore matcha's long-term effects on cognitive decline comprehensively. These studies should include larger sample sizes, more sensitive neuropsychological tests, and biomarker analyses to better understand the underlying mechanisms of matcha's effects on cognition and sleep.
Additionally, it would be beneficial to investigate whether the observed improvements in social cognition translate into meaningful changes in daily-life functioning and quality of life for older adults at risk of dementia.