A new study has found that drinking matcha, a type of green tea, may improve perception of emotions and sleep quality in older adults with a decline of cognitive functions. The study, conducted by researchers from Japan and published in the journal Alzheimer’s & Dementia, is the first long-term clinical trial to test the effect of matcha on psychological functions.
The causes of dementia are numerous, and studies have suggested that nutrition plays a key role. Matcha is a popular beverage particularly in Japan and contains ingredients such as theanine, which has been suggested to improve short-term memory and sleep.
However, no study has tested the effect of matcha on psychological functions over a long period. Hence, a collaboration was established by the University of Tsukuba between pharmaceutical manufacturing company MCBI and drinks company Ito En.
The teams aimed to investigate the effect of matcha on psychological functions and sleep in elderly adults with cognitive decline over 12 months, in addition to exploring how biological markers found in the blood and brain are related to matcha consumption.
The researchers, led by Kazuhiko Uchida, performed a double-blinded, placebo-controlled, randomized comparative clinical study. This began with recruiting 99 community-dwelling adults aged 60 to 84 years who demonstrated subjective cognitive decline (64 participants) or mild cognitive impairment (35 adults).
Subjective cognitive decline refers to a subjective feeling that memory and thinking abilities have worsened, whereas mild cognitive impairment describes an objective worsening of memory and thinking, but not severe enough to interfere with daily activities. Both conditions are risk factors for developing dementia.
The participants were randomly assigned to receive either 2 grams of matcha per day (49 participants) or the placebo capsules filled with colored corn starch (50 participants), for 12 months.
The researchers assessed the participants’ cognitive functions and sleep quality using various tests and questionnaires. They also took samples of the participants’ blood and conducted brain imaging examinations.
The results demonstrated that the matcha group improved in social acuity, which is the ability to perceive emotions based on facial expression, compared to the placebo group. The matcha group also displayed a trend towards improvement in continuous performance, which is a measure of how well an individual can maintain their attention.
Furthermore, participants who consumed matcha improved in sleep quality compared to the placebo group, as measured by the Pittsburgh Sleep Quality Index (PSQI), which is a questionnaire that evaluates various aspects of sleep such as sleep duration, and sleep disturbances.
The Mini-Mental State Examination (MMSE) was also administered, which is a test that evaluates overall cognition. A slight increase in the score was observed in the matcha group indicating improvement, while the placebo group showed a slight decrease.
The researchers also found that in the blood plasma of the participants in the matcha group, there was a reduced level of beta-amyloid 42, which is a protein fragment that accumulates in the brain of individuals with Alzheimer’s disease and is considered a biological marker of the disease.
However, the researchers did not find any change in the level of brain amyloid accumulation in either group. This was measured by a type of brain imaging scan known as amyloid-PET that detects the presence of amyloid in the brain.
Overall, the researchers concluded that “this long-term intervention study suggests that matcha consumption can improve emotion perception and attention, and sleep quality in elderly adults with cognitive decline”.
The researchers did not note any particular limitations in their publication, but the study appeared to lack control for other dietary and lifestyle factors, as well as lack assessments of mood and anxiety, all of which may have also interfered with sleep quality and cognition.
The study, “Effect of Matcha green tea on cognitive functions and sleep quality in elderly adults with cognitive decline: a randomized controlled study over 12 months”, was authored by Kazuhiko Uchida, Kohji Meno, Hideaki Suzuki, Tatsumi Korenaga, Hitomi Ito, Makoto Inoue, Liu Shan, Miho Ota, Noeru Shiraki, Shin Nakamura, Satoshi Yomota, Nobuyuki Akinaga, Yoshitake Baba, Chika Tagata, Yoshiharu Araki, Shuto Tsunemi, Kenta Aso, Shun Inagaki, Sae Nakagawa, Makoto Kobayashi, Takashi Asada, Tetsuaki Arai, and Takanobu Takihara.