Black tea, chemical extracts, cells and diabetes

“Tea could help combat diabetes,” according to the BBC News . The newspaper and other news sources report on research that found that some chemicals in black tea (theaflavins and thearubigins) mimic the action of insulin in the body. Green tea has long been marketed as having beneficial health properties and this new research suggests some possibilities for black tea.

As it was conducted in a laboratory setting and only on cells in culture, the research behind these stories can be considered 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 noted: “People shouldn’t be rushing to drink masses of black tea thinking it will cure them of diabetes”.

Where did the story come from?

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 Scientist's 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.

What kind of scientific study was this?

In this controlled laboratory experiment, the researchers looked at whether or not dietary factors played a role in the chemical pathways in the body that are involved in regulating aging and glucose formation and breakdown.

Llittle is known about the actions of polyphenols (the antioxidants that are believed to protect against cell damage) in black tea. 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.

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.

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.

What were the results of the study?

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

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

What interpretations did the researchers draw from these results?

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 was conducted in the laboratory.

• 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 on diabetes.
• The results will be of interest to researchers investigating why some studies have found drinking black tea is linked to a lower incidence of heart disease and cancer. However, while the study forms a basis for further research, it has little practical application now.

It is worth repeating: people shouldn’t drink black tea thinking it will cure them of diabetes.

Sir Muir Gray adds...

Keep taking the insulin; tea is very nice, but has no contribution to make to diabetic control.