The American Diabetes Association identifies coffee as an acceptable beverage for people with diabetes. However, coffee's impact on blood sugars can vary. According to a review published in the February 2014 issue of "Diabetes Care," the risk of developing type 2 diabetes (T2DM) decreases with coffee consumption. However coffee and the additives in coffee drinks can influence blood sugar control in those who already have diabetes. Testing blood sugars may be the best way to learn the body's response to these beverages.
A small study published in the May 2011 issue of "American Journal of Clinical Nutrition" reviewed the blood glucose effects of coffee when consumed with a meal, and found that caffeinated coffee caused more insulin resistance and higher post-meal blood sugars compared to decaffeinated coffee. An individual with insulin resistance will require more insulin to lower blood sugar compared to someone whose body uses insulin efficiently. Duke University research published in the February 2008 issue of "Diabetes Care" studied habitual coffee drinkers who had T2DM, testing their glucose levels after ingestion of caffeine supplements equivalent to four cups of coffee. Compared to a placebo, the caffeine supplements caused higher post-meal blood sugars. While the mechanism was unclear, the researchers suggested caffeine may worsen insulin resistance or affect glucose by increasing the production of stress hormones.
Decaffeinated coffee may also have an impact on blood sugar levels. Researchers who studied these effects on a small group of healthy young men published their findings in the February 2010 issue of "Diabetes Care." Within 60 minutes of consumption, decaffeinated coffee raised blood glucose more than a placebo, but less than caffeinated coffee. Research reported in the February 2011 issue of "Diabetologia," showed that decaffeinated coffee consumption improved beta cell function -- the cells that make and release insulin -- however, participants in this study did not have diabetes. Larger studies and research involving people with diabetes is needed to clearly understand the role of caffeinated and decaffeinated coffee on diabetes risk and blood sugar control in people with T2DM.
Health Benefits of Coffee
The health benefits of coffee have also been the subject of research. In addition to caffeine, coffee contains minerals and is rich in antioxidants. Researchers involved in a study showing a relationship between heavy coffee consumption and a reduced risk of diabetes explored some of these health benefits. In the May 2004 issue of "Journal of Internal Medicine," researchers suggested that chlorogenic acids, the major antioxidant family found in coffee, may protect beta cells from damage, improving insulin action and reducing diabetes risk. A review published in the November 2014 issue of "Molecules" suggested that the antioxidants in coffee have the potential to reduce inflammation -- which is linked to insulin resistance and diabetes-related complications such as cardiovascular disease.
Black coffee contains around 100 mg caffeine per 8-ounce cup and does not contain carbohydrates -- the main dietary component that affects blood glucose. However, the carbohydrates from added sugar, syrup, milk or flavored creamer can increase blood sugar in someone with diabetes. Preparing coffee at home can control these additives, and they need to be avoided when ordering coffee drinks away from home. The best options for coffee on-the-go include ordering black coffee and adding small amounts of cream or sweetener at the bar; asking for lower carbohydrate options such as sugar-free syrups, unsweetened soy or almond milk; choosing a half-sugar coffee; and always leaving off the whipped cream.
Warnings and Precautions
Research on the impact of coffee on diabetes appears inconsistent. On one hand, coffee is linked to a reduced risk of diabetes, and on the other hand, coffee leads to a short-term increase in blood sugars. More quality research is needed to more clearly understand the effects of coffee on diabetes health and blood sugar control. The coffee amount and type appear related to blood glucose effects, so anyone with diabetes needs to test their blood sugars regularly to help understand their individual response to foods and beverages, including coffee. The diabetes care team, including a registered dietitian can also be a source of information and advice. Because uncontrolled diabetes can lead to long-term health problems, anyone who struggles to control blood sugars or experiences readings consistently above or below blood sugar targets should follow up with their doctor and diabetes care team.