Posted on 01/11/2010 at 11:51:50 AM by Student BloggerBy: Jovana K.
Over the past few months I have been preparing for my upcoming comprehensive exam. The University of Toronto comprehensive exam entails a 3 hour questioning period by five well-established professors on three assigned topics. One of my topics is the role of caffeine in health and disease. Thus, for this blog I have decided to give you an overview of what I have learned.
Caffeine is a natural ingredient found in many plants, including coffee, tea, cocoa, kola, guarana and yerba mate. It is also used as a food additive in some carbonated drinks and as an ingredient in over the counter medication. In North America and Europe, up to 90% of adults regularly consume caffeine-containing beverages and foods making it the most widely consumed stimulant in the world. Current recommendations for adults are to consume less than 400 mg of caffeine per day. However, this dose is easily attained by drinking 2-3 cups of brewed coffee. My review of different brands of brewed coffees from local coffee shops revealed that Starbucks has the highest dose of caffeine, with one cup of grande coffee containing 330 mg of caffeine. So you may be wondering what are the effects of caffeine on blood glucose metabolism.
According to scientific evidence, caffeine can cross the blood-brain barrier and inhibit adenosine from binding to its receptor. Competitive antagonism of adenosine receptors increases synaptic activity and stimulates the release of neurotransmitters, particularly epinephrine. Epinephrine stimulates the central nervous system and inhibits the release of insulin. Human studies have revealed that acute caffeine intake can impair whole body insulin-mediated glucose disposal by 20-25%. This finding is likely attributed to a 50% reduction in skeletal muscle glucose uptake. However, despite these findings it remains unclear whether caffeine intake poses a risk for diabetes in healthy adults because most people develop a tolerance to caffeine with long-term consumption. Disturbances in insulin-mediated glucose disposal may have important health implications in individuals already experiencing insulin resistance such as those seen in obese patients, type 2 diabetics and pregnant women. Exposure to high levels of caffeine during pregnancy has the potential to increase insulin resistance and/or impair maternal blood glucose tolerance, which in turn may alter fetal development.
Importantly, the aforementioned effects of caffeine cannot be generalized to coffee because coffee contains many bioactive substances some of which can attenuate the adverse effects of caffeine on blood glucose metabolism. For example, coffee contains high concentrations of chlorogenic acid and guinide, which have been shown to decrease glucose absorption and enhance muscle glucose disposal. Emerging epidemiological evidence indicates that habitual coffee consumption (both caffeinated and decaffeinated) can decrease the risk of developing type 2 diabetes in healthy adults. However, it is still premature to recommend coffee consumption as a public strategy for prevention of type 2 diabetes. Further research should identify the genetic factors that may modulate how coffee and caffeine affect glucose metabolism. For more information I recommend reading the following reviews: