You may have been puzzled by a slight rise in blood sugar even though you just had a cup of black coffee. Researchers are beginning to uncover some insight into the relationship between our favorite drinks and diabetes.

Coffee has been associated with a reduced risk of developing diabetes. Caffeinated and decaffeinated coffee may have components other than caffeine that reduce blood glucose concentrations. But take the caffeine out of the coffee, and the caffeine will increase blood sugar up to 8% according to a recent study. This one study was conducted on 10 people with type 2 diabetes, using caffeine capsules. The dose was an equivalent of drinking 4 cups of coffee. How caffeine might raise blood sugar is unclear, perhaps a surge of adrenalin or cortisol elevates blood sugar, or caffeine alters the function of insulin. This small study opens up more questions, and hopefully more conclusive research will follow.

A study reported in Diabetes Care, March 2009, examined the effect of decaffeinated coffee on blood sugar levels in 15 overweight men (non-diabetics). The components in decaffeinated coffee, chlorogenic acid and trigonelline (also present in caffeinate coffee) reduced the glucose and insulin response for 15 minutes after ingestion of glucose in a standard OGTT, and then no longer effects.

So, if you are a coffee drinker and frustrated by less than desired blood sugar control, consider switching to decaffeinated coffee. This small study was done with larger amounts of caffeine, so lesser intake of coffee may have minimal effects. More is yet to be known.

Tea is a more widely used beverage than coffee, and has been used for medicinal purposes for centuries. Tea contains polyphenols - chemicals that have anti-cancer, anti-inflammatory and antioxidant effects. Tea also contains caffeine, and in a few studies, using oolong tea and green tea, have been shown to decrease blood glucose levels, improve A1C, total cholesterol and LDL cholesterol levels. Drinking green tea may lower the risk of developing type 2 diabetes.

Teas have some side effects and interfere with nutrients and drug action if consumed in large or excessive quantities. Tea may interfere with the absorption of iron from food. Tea may also interfere with certain labs tests, thallium tests, uric acid tests, and vanillylmandelic acid concentrations. Tea may also worsen glaucoma due to increase eye pressure. Excessive amounts may cause insomnia, anxiety and restlessness, and increased bleeding if used with blood thinners. Again, excessive and continuous drinking of tea may have these effects, but the intake of a few cups of tea or glasses of iced tea a day are innocuous.

Reviewed by Clara Schneider MS, RD, RN, CDE, LDN - 05/13