Blood sugar levels are mainly affected by eating carbs, the various sugars found in baked goods, pasta, dairy, fruit and veggies. Your pancreas secretes insulin so blood glucose can enter your cells and animate your busy body and fuel your clever brain. Compounds in tea leaves impact sugar metabolism and insulin secretion, although adding dairy and sweeteners to tea impacts blood sugar levels to a greater extent. Drinking tea plain may seem boring, but it's a healthy strategy for diabetics.
Controlling blood sugar levels is important for health in many ways, especially for diabetics who have problems either producing insulin or responding to insulin. Too much sugar in the blood is toxic to nerves, blood vessels and other tissues, whereas too little can leave you feeling weak, fatigued and grouchy. Lactose, the main sugar in milk and cream, and various sweeteners such as table sugar, brown sugar and honey are commonly added to hot and cold tea. Dairy and simple sugars are easily reduced to glucose in your intestines and then quickly absorbed into your bloodstream. Consequently, if you add milk or sugar to your tea, they will increase your blood glucose levels until enough insulin is released to transport it into your cells.
Green tea is rich in antioxidants called polyphenols. Antioxidants help prevent tissue damage by destroying free radicals, but the polyphenols found in green tea leaves also help to lower blood sugar levels. The polyphenols, especially EGCG and other catechins, work by inhibiting the actions of amylase, an enzyme needed to metabolize starch and some other sugars. The result is that the sugars remain mostly undigested and are unable to make much of an impact on blood glucose levels. EGCG also increases glucose absorption by cells, which mimics the actions of insulin, and inhibits the liver’s production of glucose.
Black tea leaves also contain polyphenols, but not nearly as much as green tea, so their impact on blood sugar is not as strong. Some catechins found in black, green and white teas reduce how much glucose is absorbed through the intestines, which prevents blood sugar levels from rapidly rising. These catechins inhibit the activity of alpha-glucosidase, an enzyme that allows glucose absorption by the small intestine. Black tea leaves contain more tannins and caffeine than green tea, although these compounds don’t seem to impact blood sugar levels or insulin secretion.
Herbal teas include essentially any plant compound, aside from actual tea leaves, that you can steep in hot water and drink. Every herb affects your body in some way, but the most common herbal teas such as chamomile, peppermint and lavender have virtually no impact on blood sugar levels or insulin release, assuming no sweeteners are added. Some fruity herbal teas contain freeze-dried fruit or artificial flavors, which can mildly influence blood sugar, so read the ingredient labels carefully if you need to monitor your levels.
- Natural Standard Herb & Supplement Reference: Evidence-based Clinical Reviews; Catherine E. Ulbricht and Ethan M. Basch
- PDR for Herbal Medicines; PDR Medical Staff
- Principles and Practice of Phytotherapy: Modern Herbal Medicine; Simon Mills and Kerry Bone
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.