Both types of tea block cell-poisoning effects of plaque-forming amyloid protein
by Craig Weatherby
It seems that tea may fit brain health to a "T".
As we reported last month, the results of a Japanese study in people aged 70 or older suggest that green tea may reduce the risk of mental decline (Kuriyama S, 2006), with the lowest risk of mental decline being associated with drinking at least two cups of green tea per day (See “Tea May Combat Women’s Cancers and Help Keep Seniors Mentally Sharp”).
Hard on the heels of those findings come new research results from Canada, which suggest that the image of the spry, tea-drinking septuagenarian—or even nonagenarian—with a twinkle in his or her eye may be more than a wishful, sentimental representation.
The study was performed in rat cells from the hippocampus—a part of the brain key to rodent and human memory—suggests that both black and green tea may be equally powerful allies against the cell-killing protein plaque associated with Alzheimer’s disease (AD).
Results that the Canadian team reported (Bastianetto S, 2006) confirm that compounds in green and black tea can block the toxic effects of amyloid proteins, which form the brain-coating plaques characteristic of Alzheimer’s disease.
And this study—performed by Rémi Quirion, Ph.D. and colleagues at Quebec’s Douglas Hospital Research Centre—is not the first whose results suggest that tea flavanols can protect against amyloid toxicity.
A study in human brain cells (Levites Y 2003) showed that tea flavanols can protect against amyloid toxicity, and do it in the kind of dose-dependent manner that further confirms the reality of the effect.
Black tea equals green for brain-protecting power
The compounds found to cut the toxic effects of amyloid proteins are the same flavanols associated with tea’s anti-cancer and heart-health properties.
While green tea contains more of the three flavanol antioxidants that showed the greatest protective power—gallic acid (GA), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG)—exposure to identical amounts of black or green tea extract produced the same protective effects.
This equity of effect was something of a surprise, since black tea contains only half as much of these specific flavanol antioxidants, compared with green tea.
To make black tea, green tea leaves are crushed and heated to promote fermentation: a process that results in oxidation of a portion of their flavanols. Oxidation polymerizes (links together in chains) a portion of the fresh leaves’ flavanols, creating new compounds called theaflavins and even larger flavanol chains called thearubigens, which give black tea its characteristic astringency, briskness, and bright, reddish-brown colors.
(We should note that white tea is the richest source of the amyloid-busting flavanols—GA, ECG, and EGCG—because while green tea is slightly fermented/oxidized and black tea is heavily fermented/oxidized, white tea is almost completely unfermented/oxidized.)
But, despite its reduced flavanol content versus green tea, black tea extract appears to exert just as powerful a protective effect against amyloid proteins, at least in isolated rat brain cells.
The protective effects took two forms:
- EGCG and GA kept amyloid proteins from aggregating, which could result in plaque formation.
- EGCG and GA stopped formation of potentially toxic amyloid derivatives that can pass through cell membranes.
Want to stay mentally sharp? These discoveries indicate that you may be able to preserve mental acuity longer by drinking the tea of your choice, green or black.
- Kuriyama S, Hozawa A, Ohmori K, Shimazu T, Matsui T, Ebihara S, Awata S, Nagatomi R, Arai H, Tsuji I. Green tea consumption and cognitive function: a cross-sectional study from the Tsurugaya Project 1. Am J Clin Nutr. 2006 Feb;83(2):355-61.
- Bastianetto S, Yao ZX, Papadopoulos V, Quirion R. Neuroprotective effects of green and black teas and their catechin gallate esters against beta-amyloid-induced toxicity. Eur J Neurosci. 2006 Jan;23(1):55-64.
- Levites Y, Amit T, Mandel S, Youdim MB. Neuroprotection and neurorescue against Abeta toxicity and PKC-dependent release of nonamyloidogenic soluble precursor protein by green tea polyphenol (-)-epigallocatechin-3-gallate. FASEB J. 2003 May;17(8):952-4. Epub 2003 Mar 28.