The US research led by Lisa Striegel from Framingham State University analysed black tea leaves after being immersed in hot water.
They extracted a number of polyphenols - antioxidants - all of which were shown to block enzymes that push up blood sugar from the digestion of carbohydrates.
They had 'significant activity' against the enzymes, alpha amylase and alpha-glucosidase.
This suggests that black tea extract may reduce levels of glucose normally associated with these digestive enzymes, says a report in Frontiers of Nutrition.
In a second study from Japan, a freeze dried powder extract of black tea leaves was found to have a similar effect on the two enzymes.
The study from the Hokkaido Pharmaceutical University School of Pharmacy was published in the Journal of Ethnopharmacology.
Although black tea was analysed in the study, other research in humans suggests adding milk does not dilute the benefits.
Dr Catherine Hood from the industry backed Tea Advisory Panel (TAP) said 'Diabetes is a condition of disordered glucose metabolism.
'The main source of glucose in the body comes from the digestion and hydrolysis of dietary carbohydrates.
'The digestive enzymes pancreatic alpha-amylase and the intestinal alpha glucosidases are responsible for digesting carbohydrates to form glucose.
'Inhibition of these enzymes and hence the inhibition of glucose formation could contribute to the prevention and management of type 2 diabetes.'
Previous reviews involving almost 300,000 people found those who drank three to four cups a day enjoyed a 25 per cent lower chance of developing type 2 diabetes compared with those drinking tea occasionally or not at all.
Australian researchers ruled out the effects of caffeine, saying other ingredients such as magnesium and antioxidants may be responsible.
Dr Tim Bond from TAP said the studies provided additional evidence that around three cups of tea a day might produce anti-diabetic benefits.
He said 'Tea is a very popular beverage in the UK and these latest findings together with many other published studies continue to suggest that Britain's' favourite beverage is good for our health including our heart and vascular system.'
Almost 80 per cent of Britons are tea drinkers and they get through an estimated 165 million cups every day.
The British tea industry is estimated to be worth more than £700million a year.
Antioxidants known as flavonoids found in tea are thought to control inflammation, reduce excess blood clotting, promote blood vessel function and limit furring up of the arteries.
- Daily Mail
