Black tea may beat diabetes



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March 3, 2008  
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black-tea1.jpgCM NEWS, NHS news - “Scientists claim a cup of tea may help cure diabetes,” according to the Daily Mirror. The Daily Mirror and other news sources (BBC) report on research that found that some constituents of black tea (theaflavins and thearubigins) mimic the action of insulin in the body. For a long time green tea has been believed to have beneficial health properties and it is now suggested that black tea may also have some potential.

What are theaflavins? Theaflavins are a flavonoid found in tea. Theaflavins are considered the active ingredient in the fight against high cholesterol. Theaflavins are produced as green tea ferments into black or oolong tea. In addition to fighting cholesterol, theaflavins also support lipoprotein metabolism. Theaflavin often works with the other polyphenols in tea to protect and enhance the body’s functions.

What are thearubigins? Thearubigins are polymeric polyphenols that are formed during the enzymatic oxidation (called fermentation by the tea trade) of tea leaves.

A large concentration of thearubigin is therefore found in black (fully oxidated) teas, and a very low concentration in unoxidized teas such as white and green teas. The health benefits of oxidized teas can be partially attributed to the antioxidant properties of thearubigins.

While unoxidized tea lacks a high concentration of thearubigins, it still has antioxidant properties which are primarily due to its high concentration of catechin type polyphenols. Catechins are converted to theaflavins such as thearubigin during the oxidation process.

Amy Cameron and colleagues from the University of Dundee and University of Edinburgh carried out the research. The study was funded by the Caledonian Research Foundation, the Chief Scientists Office of the Scottish Executive, the Medical Research Council, and scholarships from the Carnegie Trust for the University of Scotland. The study was published in the peer-reviewed medical journal: Aging Cell.

In this controlled laboratory experiment, the researchers investigated if dietary factors could play a role in the chemical pathways in the body that are involved in regulating aging and glucose formation and breakdown.

As tea is one of the most popular drinks consumed globally, and little is known about the actions of polyphenols from black tea (the antioxidants that are believed to protect against cell damage) in humans, the researchers hoped that further research would reveal how age-related metabolic diseases (such as diabetes) can be delayed or prevented.

The rate of ageing in the body is believed to be regulated by a group of molecules known as FOXO transcription factors. Both insulin and insulin-like growth factor-1 (IGF-1) have been found to inhibit FOXOs. The researchers were particularly interested in one type of FOXO molecule – FOXO1a – which is known to prevent glucose production in the liver by suppressing certain genes.

What is FOXO? FOXO proteins are a subgroup of the Forkhead family of transcription factors. This family is characterized by a conserved DNA-binding domain (the ‘Forkhead box’, or FOX) and comprises more than 100 members in humans, classified from FOXA to FOXR on the basis of sequence similarity.

These proteins participate in very diverse functions: for example, FOXE3 is necessary for proper eye development, while FOXP2 plays a role in language acquisition. Members of class ‘O’ share the characteristic of being regulated by the insulin/PI3K/Akt signaling pathway.

To investigate if certain dietary factors can mimic the effects of insulin and IGF-1 on FOXOs, the researchers carried out laboratory experiments using human kidney cells called “293 cells” and rat liver cells.

Want to know more?Originally, tea was valued for its medicinal qualities. (source)

It has long been known that tea aids in digestion, which is why many Chinese prefer to consume it after their meal. The elevation of tea drinking to an art form began in the 8th century, with the publication of Lu Yu’s “The Classic Art of Tea.” The highly esteemed poet and former Buddhist priest had strict notions about the proper procedure for brewing, steeping, and serving tea.

4 basic categories of teas:

White tea: Reputed to provide the most health benefits, white tea is made from immature tea leaves that are picked shortly before the buds have fully opened.

Green tea: Green teas are not fermented during processing, and thus retain the original color of the tea leaves. The most famous green tea is the expensive Dragon Well tea, grown in the hillsides of Hanghou.

Black tea: also known as “red tea,” black teas are made from fermented leaves, which accounts for their darker color. Popular varieties of black tea include Pu-Er (Cantonese “Bo lei”), a Cantonese tea often drunk with dim sum, and Lu-An (Cantonese “Luk on”) – a milder tea favoured by the elderly. Finally, oolong teas are partially fermented, resulting in a black-green tea.

Scented tea: Scented teas are made by mixing various flowers and petals with green or oolong teas. The best known among these is jasmine tea.

Recognised laboratory procedures were used in which selected black tea compounds (theaflavins and thearubigins) were incubated with the cells in order to examine their effects. These effects were compared to those observed when a chemical, dimethyl sulfoxide (DMSO), was used as a control.

The researchers then compared the differences between the effects of tea and the control on the activity of FOXO1a and certain genes using statistical methods.

The researchers found that three different types of theaflavins induced similar chemical changes in FOXO1a to those that are made by insulin and IGF-1.

They also found that the theaflavins suppressed the PEPCK genes that are involved in glucose processing in the liver. The effects were greater with increased dosage of the tea compound.

As it was conducted in a laboratory setting and only on cells in culture, the research behind these stories could be considered as preliminary. This research has not investigated whether giving black tea to a living person has any effect on glucose regulation in a way that is similar to insulin or diabetic medications. As one of the researchers quite aptly stated, “People shouldn’t be rushing to drink masses of black tea thinking it will cure them of diabetes”.

The authors say that their experiments have identified a group of tea compounds that have similar insulin-like effects on FOXO1a and PEPCK that are “key downstream effectors of cellular insulin/longevity signalling.”

They say that “it remains to be established whether black tea polyphenols are sufficiently bioavailable to act in vivo [in the body]”, but suggest that developments may lead to the production of drugs or certain dietary interventions which can treat or delay the onset of age-related diseases.

What does the NHS Knowledge Service make of this study?

This early experimental research has been conducted in the laboratory setting only.

  • The study has not investigated whether giving black tea to an individual has a similar effect on glucose regulation in the body as insulin or diabetic medications, and makes no conclusions or assumptions about any beneficial properties of black tea compounds upon diabetes.
  • The results will be of interest to other researchers investigating why some studies have found drinking black tea to be associated with a lower incidence of heart disease and cancer. However, while the study forms a basis for further research, it has very little practical application now.

As the researchers stated, people shouldn’t drink black tea thinking it will cure them of diabetes.

[Aging Cell 2008; 7: 69–77]