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Nutrient - Green tea antioxidants may help ward off Alzheimer's

By Dr Pieris Nicola PhD BSc (Hons) Dip ION

According to the latest research by scientists at Newcastle University, regularly drinking green tea could help protect the body against some of the common diseases we face today, including Alzheimer’s disease, other forms of dementia, and cancer.

Alzheimer’s disease is one of the main causes of elderly dementia. Although the exact cause of Alzheimer’s is a topic of debate, the consensus is that a protein called beta-amyloid plays a significant role in the development of this disease. Beta-amyloid protein is toxic to brain cells and previous evidence suggests that this toxicity may be caused by the free radicals generated by this protein, in particular hydrogen peroxide. 

Free radicals are nasty chemicals generated by sunlight, cigarette smoke, and air pollution. They are also formed naturally in the body – for example, when food is converted to energy. Free radicals are capable of damaging cells and genetic material, and may contribute to the development of chronic diseases including cardiovascular disease, vision loss, cancer and Alzheimer’s disease. 

We are not defenceless against free radicals. Our body produces molecules that quench free radicals. We also extract free radical fighters, called antioxidants, from food. A number of foods are especially rich in antioxidants, including green tea.

Tea is the second most widely consumed beverage in the world, right behind water. According to Chinese legend, the Emperor Shen Nung, the earliest known practitioner of herbal medicine, discovered green tea in 2737 BC, after some of the dried leaves fell into his cup of boiling water. 

Green tea is known to contain natural polyphenol antioxidants, including catechins and flavanols (a type of flavonoid abundant in green tea). Catechins and flavanols are natural free radical fighters.  However, researchers have, up until now, largely ignored the effects of digestion on the free radical scavenging activity of green tea polyphenols.  Digestion is a vital process that breaks down food and drink into their smallest parts, so the body can use them to build and nourish cells and to provide energy. The process of digestion could potentially alter the structure of the catechins and flavanols present in green tea, as well as their free radical fighting activity. Led by Dr Ed Okello, the research team from the Medicinal Plant Research Group at the School of Agriculture in Newcastle University wanted to know if the protective properties of green tea, which were previously shown to be present in the freshly brewed form, were still active once the tea had been digested. 

The Newcastle team worked in collaboration with the Scottish Crop Research Institute in Dundee, who developed technology, which simulates the human digestive system. 

The researchers first brewed a pot of green tea, and then concentrated the mixture. The mixture was then treated to mimic the effects of normal digestion using enzymes and chemicals found in the stomach and small intestine, including acid, pepsin, bile salts and pancreatin. Following digestion, the polyphenols present in green tea are broken down to produce a mixture of compounds, which represent the green tea chemicals that are potentially bio-available to us. 

The researchers detected over 30 major polyphenols that remained active after being “digested.” The digested green tea extract was then tested for its ability to protect nerve cells against death caused by beta-amyloid protein and hydrogen peroxide. 

The researchers did this by exposing the nerve cells to concentrations of hydrogen peroxide or beta-amyloid sufficient to kill about half of the cells treated; and to varying concentrations of the digested green tea extract, to see if it could prevent cell death. 

The results, published in the academic journal Phytomedicine, showed that the digested green tea extract significantly protected the nerve cells from the toxic effects of hydrogen peroxide, even at low concentrations. Low concentrations of the digested green tea extract were also able to protect the cells against death caused by beta-amyloid. 

As an added bonus, the digested green tea extract was also shown to significantly slow down the growth of cancer cells. 

Dr Okello commented: "What was really exciting about this study was that we found when green tea is digested by enzymes in the gut, the resulting chemicals are actually more effective against key triggers of Alzheimer's development than the undigested form of the tea. 

"In addition to this, we also found the digested compounds had anti-cancer properties, significantly slowing down the growth of the tumour cells which we were using in our experiments." 

The next step for the group is to determine if these beneficial products of polyphenol digestion are produced in healthy human volunteers after they consume tea. The team has already secured funding from the Biotechnology and Biological Sciences Research Council to take this forward.

Dr Okello said: "There are obviously many factors which together have an influence on diseases such as cancer and dementia – a good diet, plenty of exercise and a healthy lifestyle are all important. But I think it's fair to say that at least one cup of green tea every day may be good for you and I would certainly recommend it."

Article References

Okello EJ, McDougall GJ, Kumar S et al. In vitro protective effects of colon-available extract of Camellia sinensis (tea) against hydrogen peroxide and beta-amyloid (A((1-42))) induced cytotoxicity in differentiated PC12 cells. Phytomedicine 2010 Dec 21. [Epub ahead of print].

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