Black tea shows blood sugar benefits

The study, a four-way randomised, crossover trial, suggests that Britain's top tipple could have benefits for diabetics to blunt the blood sugar spikes, keeping the body's blood sugar levels relatively steady throughout the day.

This has been linked to better regulation of appetite and a reduced tendency to snack.

Researchers from King's College London and the University of Central Lancashire recruited 16 healthy subjects and assigned them to drink 75 grams of glucose in either 250ml of water (control), 250ml of water plus 0.052g of caffeine (positive control) or 250 ml of water plus 1.0 or 3.0 grams of instant black tea.

Writing in the Journal of the American College of Nutrition , the researchers report that plasma glucose concentrations during the first hour in response to the drinks were not significantly different.

However, after two hours plasma glucose concentrations were significantly in the group who consumed 1.0 grams of tea, relative to the control and caffeine drinks.

Moreover, drinking the black tea was associated with increased insulin levels compared with the control and caffeine drinks at 90 minutes.

The health benefits of tea, including protection from certain cancers and Alzheimer's, have been linked to the polyphenol content of the tea.

Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent.

The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.

Chemical analysis showed that the tea was rich in polyphenolic compounds (total, 350mg/g).

Bryans and co-workers state that the polyphenol content of the tea was most probably behind the effects.

They state that these compounds could have an insulin-stimulating effect on pancreatic B-cells - cells responsible for insulin production.

"It is important to note also that the physiological effects seen in this study were relatively small and were achieved under test conditions.

"Under normal tea drinking conditions before or after food, the presence of other phenolic compounds could potentially alter, or even enhance, the effects seen in our study.

"It is certainly an area of research that warrants further investigation," they concluded.

The global tea market is worth about €790m (£540m, $941m).

Green tea accounts for about 20 per cent of total global production, while black tea (green tea that has been oxidized by fermentation) accounts for about 78 per cent.

Source: Journal of the American College of Nutrition Volume 26, Number 5, Pages 471-477 "The Effect of Consuming Instant Black Tea on Postprandial Plasma Glucose and Insulin Concentrations in Healthy Humans" Authors: Judith A. Bryans, P.A. Judd, P.R. Ellis