Coffee vs. Tea

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By now, most people with diabetes are used to hearing about studies that show benefits from certain foods, such as the apparent blood-glucose-lowering effects of vinegar and cinnamon. Sometimes, these studies imply support for routines that would take some getting used to, such as drinking a vinegar solution before every meal. But other times, they support behaviors that would be easy to adopt and that you might even follow already. Such is the case when it comes to the protective effects of coffee and tea on blood glucose control. For many people, the question isn’t whether to indulge in one of these beverages, but instead which one makes for a healthier habit.

Most recently, a study published last week by the journal BMJ (formerly British Medical Journal) found that countries in which black tea consumption is highest showed the lowest levels of Type 2 diabetes. According to an article on the study published in Britain’s Daily Mail, sales data showed that Ireland consumed the most black tea per capita, followed by Britain and Turkey. These countries showed lower levels of Type 2 diabetes than countries where tea consumption is low, including Brazil, Morocco, and Mexico. While it is possible than many other factors could have affected the relative rates of Type 2 diabetes in these countries, it is notable that the study investigated a link between black tea and various medical conditions — and found a link only with Type 2 diabetes, along with a lesser link with obesity. Researchers speculated that the beneficial effects of black tea might come from substances known as flavonoids, which result from the fermentation of green tea (which has also been found to be beneficial in diabetes) into black tea.

Coffee, on the other hand, also has a large body of evidence to support both preventive and therapeutic effects when it comes to diabetes. As David Spero noted in a blog post last year, a study conducted at UCLA found that women who drink four cups of coffee each day are less than half as likely as those who drink no coffee to develop Type 2 diabetes. Some studies, however, have found that regular caffeinated coffee has greater beneficial effects than decaf coffee, while others have found similar benefits. And yet other studies have found that caffeine can harm blood glucose control in people with diabetes. Coffee, notably, tends to contain more caffeine than black tea (which, in turn, has more caffeine than green tea).

As Web Editor Diane Fennell noted in a blog post three years ago, a meta-analysis (analysis of several studies) that year found that drinking decaf coffee actually led to a lower risk of developing Type 2 diabetes than drinking regular coffee, with three to four cups daily reducing the risk by 33% versus 25%, respectively. The same level of tea was found to reduce the risk by about 20%. One factor that is difficult to control for among different studies is the strength of these beverages; many countries in which tea is an entrenched part of the culture, for example, tend to drink stronger tea than is typical in other countries. And even within countries, varying beverage strengths may be common.

Do you drink coffee or tea? Do you believe that either beverage has beneficial, or harmful, effects on your blood glucose control? What factors have led you to drink coffee, tea, or neither one? Would you switch beverages if evidence strongly favored one over the other? Leave a comment below!

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