The study focused on the role of antioxidant potential of green tea and its constituents to counter the oxidative stress induced by a build up of beta-amyloid protein.
The build-up of plaque from beta-amyloid deposits is associated with an increase in brain cell damage and death from oxidative stress.
This is related to a loss of cognitive function and an increased risk of Alzheimer's, the most common form of dementia and currently affects over 13 million people worldwide.
The direct and indirect cost of Alzheimer care is over $100 bn (€ 81 bn) in the US, while direct costs in the UK are estimated at £15 bn (€ 22 bn).
The new study, published in the April issue of the Journal of Nutritional Biochemistry , reports the effects of green tea extracts in the form of Mitsui Norin's commercial Polyphenon E (PE) on the cognitive learning ability of rats.
The concentration of catechins was classified as 63 per cent EGCG, 11 per cent epicatechin (EC), six per cent epigallocatechin (EGC), and six per cent epicatechin gallate (ECG).
"Our results suggest that long-term administration of PE prevents cognitive deficits caused by oxidative stress, beta-amyloid-induced and/or otherwise, at least by facilitating antioxidative defences," wrote lead author Abdul Haque from Shimane University Faculty of Medicine Despite the promising results, as well as a substantial body of epidemiological studies reporting a protective effect of green tea for Alzheimer's, the researchers stressed that further research was required, particularly to clarify the mechanism.
Moreover, it is not known if such results would be repeatable in humans.
Study details Haque and co-workers took five-week old Wistar rats and randomly assigned them to one of two groups - one acted as the control group and received no tea extract, while the other group has its drinking water supplemented with 0.5 per cent PE.
After 26 weeks, an eight-arm radial maze was used to test the animals' learning ability.
Twenty weeks later, the two groups were divided again into two, one to continue as before, while the other groups were infused with beta-amyloid protein to induce oxidative stress.
The animals receiving the green tea extract should significantly decreased beta-amyloid-induced changes to the reference and working memory, while levels of reactive oxygen species (ROS) were 42 per cent less than the controls animals infused with the protein.
"In this study, the intake volume of PE-mixed water was approximately 60 ml/kg/day in the 0.5 per cent PE group," explained the researchers.
"Based on this water volume intake, a person (with a body weight of 50 kg) would have to drink about three litres of PE per day to get similar effects.
"However, humans consume antioxidants (including vitamins A, B, C and E as well as polyphenols, etc.) from various food sources everyday.
Therefore, a lower amount (less than three litres) of 0.5 per cent PE-mixed water volume intake may be effective in humans to ensure the similar effects.
"However, detailed investigation is certainly required to understand the fate of catechins in humans."
Global tea market The global tea market is worth about €790 (£540, $941) million, with green tea accounting for about 20 per cent of total global production, while black tea accounts for about 78 per cent.
Green tea is said to contain over four times the concentration of antioxidant catechins than black tea (green tea leaves that have been oxidized by fermentation), about 70 mg catechins per 100 mL compared to 15 mg per 100 mL for black tea.
Consumer awareness of the benefits of green tea and green tea extracts continues to rise with growing numbers of studies, from 430 papers in 2000 to almost 1500 in 2003, reporting benefits of the main compounds, catechins.
This has seen European demand surge, having reached 500 metric tonnes in 2003.
Companies such as DSM, with its Teavigo boasting 95 per cent purity of epigallocatechin gallate (EGCG), and Taiyo International, with its Sunphenon claiming more than 90 per cent purity, position themselves firmly in specific catechin markets.
Source: Journal of Nutritional Biochemistry Published online ahead of print, doi: "Green tea catechins prevent cognitive deficits caused by A-beta-1-40 in rats" Authors: Abdul M. Haque, M. Hashimoto, M. Katakura, Y. Hara, O. Shido