Two grams per day of a green tea powder for three months were associated with significant improvements in the Mini-Mental State Examination (Japanese version) score of 12 elderly nursing home residents with cognitive dysfunction.
“These results support the findings of previous epidemiological studies, and additionally demonstrate that green tea improves cognitive function or reduces the progression of cognitive dysfunction even at the relatively low catechin and theanine concentrations that can be obtained from ordinary levels of daily green tea intake,” wrote scientists from the University of Shizuoka and Ito En Ltd in the journal Nutrients.
“The green tea powder used as a daily dose in this study contained as its main bioactive components 227 mg of catechins and 42 mg of theanine, concentrations that are approximately equal to two to four cups of bottled or home-brewed green tea.”
The study adds to an ever-growing body of science supporting the potential benefits of green tea and its constituents, most notably EGCG (epigallocatechin gallate). To date green tea has been linked to a reduced risk of Alzheimer's and certain cancers, improved cardiovascular and oral health, as well as benefits in weight management.
Green tea contains between 30% and 40% of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3% and 10%. Oolong tea is semi-fermented tea and is somewhere between green and black tea. The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).
The Japanese researchers recruited 12 elderly people with an average age of 88 to participate in their pilot study. All participants consumed the two grams per day of the green tea powder (manufactured by Ito En Ltd) for three months. They all took the Mini-Mental State Examination Japanese version (MMSE-J) at the start and the end of the study.
Results showed that MMSE-J scores improved significantly from an average of 15.3 at the start to 17.0 at the end of the study. Drilling into the data revealed that short term memory in particular was improved.
The researchers also reported that triglyceride levels decreased in the participants, but not changes were observed for blood pressure, blood glucose, or cholesterol levels.
Commenting on the potential mechanism of action, the researchers postulated that the anti-oxidative and anti-inflammatory properties of catechins and theanine in green tea may have been behind the benefits.
Other mechanisms were also proposed, including an effect of tea polyphenols on acetylcholinesterase (a target for Alzheimer’s disease medications), or on stress control, which impacts cognitive function.
“In particular, research on acetylcholinesterase inhibition has shown that tea polyphenols, including catechins and theanine, also blunted […] learning and memory impairment in model mice,” they wrote.
“Our results suggest that green tea consumption may be effective in improving cognitive function or reducing the progression of cognitive dysfunction in elderly individuals, and that it may similarly reduce the progression of vascular dementia,” they added.
“Additional long-term large-scale randomized controlled studies are needed both to establish evidence for the effect of green tea consumption on cognitive dysfunction, and to reveal the relationship between this effect and atherosclerotic risk factors.”
2014, Volume 6, Number 10, Pages 4032-4042; doi:10.3390/nu6104032
“Green Tea Consumption Affects Cognitive Dysfunction in the Elderly: A Pilot Study”
Authors: K. Ide, H. Yamada, N. Takuma, et al.