Components of black tea can mimic the action of insulin and could have the potential to combat type 2 diabetes and the ageing process. Scottish scientists added various tea polyphenols (theaflavins and thearubigins) to human cell cultures and investigated the effect on genes involved in glucose metabolism and regulation of cellular ageing processes. 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 FOXO1a, which is known to prevent glucose production in the liver by suppressing certain genes. They found that three different types of theaflavins induced dose-dependant changes in FOXO1a similar to those caused by insulin and IGF-1. They also found that the theaflavins suppressed other genes involved in glucose processing in the liver. The authors conclude that they have identified a group of tea compounds that are key downstream effectors of cellular insulin/longevity signalling.

Black tea polyphenols mimic insulin/insulin-like growth factor-1 signaling to the longevity factor FOXO1a. Aging Cell. 2008 Jan;7(1):69-77.