“Drinking a cup of tea can help prevent diabetes”
Hardly a week goes by without some sensationalist headlines that tell us that certain drinks or foods are good or bad for us. We have been told that drinking coffee is good for our liver, drinking tea or eating blueberries have anti-diabetic properties, drinking cocoa fends of Alzheimer’s whilst exercise makes us age faster. I do find these quite fascinating as quite often we feel secretly guilty about our little pleasures (5 cups of tea a day for example) or not doing enough exercise. Reading headlines like these do tend to make us feel quite good about our lifestyle choices; however, once these headlines do grab our interest, it would be quite nice to check out the original article(s) on which the claims were made.
Last week, another such headline appeared in the Independent; it stated “Drinking a cup of tea can help prevent diabetes, new research shows”. As somebody who has been working on the complexity of this disease for 16 years now, my immediate reaction was “really, how”? Well, as a nation of tea drinkers, we are sorted then! Strange however that the most recent statistics from the NHS suggest there are approximately 3.1 million adults with diabetes in the UK, with the number expected to rise of 4.6 million by 2030.
Diabetes is a disease characterized by high glucose levels in the blood. There are two major types; type 1 diabetes and type 2 diabetes. Whilst type 1 is normally the one that occurs early in life and quite often with genetic susceptibility, type 2 diabetes used to be associated with “old” age. However, this is changing rapidly because of the increase in the obesity levels within our population. The disease manifests itself a lot earlier and 90% of diabetes cases are type 2. For example, the UK has the highest rate of child obesity in Western Europe, which is estimated to cost the NHS about £4.2bn a year. Children under 10 years of age are already exhibiting some of the risk factors associated with type 2 diabetes as well as cardiovascular disease. So if there is any truth in the tea story, we certainly need to know about it!
So what has the original study reported? The authors made several different extracts of black tea (~80% tea consumption is from black tea) and investigated the effects of these tea extracts (fermented tea) versus a black tea pomace that they made on the activity of certain enzymes (e.g. α-glucosidase) thought to play an important role on the ability of the organism to process glucose. They found that the α-glucosidase inhibitory activity increases as tea is fermented, so the longer we brewed the tea, the better effects we would get. Overall, the authors found that both black tea water extract and black tea pomace (which was a lot more potent than just the brewed tea) could inhibit this enzyme, α-glucosidase, thus suggesting that this could in turn have anti-diabetic properties.
There have been numerous other studies that have examined the green or black tea extracts (fermented tea) in animal models of diabetes, and similarly have found that these could decrease glucose levels in rats. Some of those effects were attributed to its antioxidant properties, similarly to cinnamon, blueberries and other natural products.
So how about that article “Drinking a cup of tea can help prevent diabetes”? Well the researchers did not actually show how much tea one would need to drink to get any beneficial effects and none of it was tested in people. The fact that the best results were obtained using black tea pomace suggests that concentrated amounts may be necessary to get the beneficial effects. However, as long as we don’t add in sugar to our tea, it appears that it would be worth sticking to our long tradition of having an afternoon cup of tea after all.
Streigel, L. et al. (2015). Effect of black tea and black tea pomace polyphenols on α-glucosidase and α-amylase inhibition, relevant to type 2 diabetes prevention.. Frontiers in Nutrition. DOI:10.3389/fnut.2015.00003
Gomes, A. et al. (1995). Anti-hyperglycemic effect of black tea (Camellia sinensis) in rat. Journal of Ethnopharmacology. DOI:10.1016/0378-8741(95)01223-Z