A Closer Look at Coffee and Diabetes

A Closer Look at Coffee and Diabetes

Recently, research at Duke University has suggested that caffeine seems to increase the levels of blood sugar over the course of a day. How does that jive with the numerous studies that show coffee consumption lowers the risk of Type 2 diabetes? There are a number of reasons for the apparent contradiction – and we do stress the word ‘apparent’ in that sentence. A closer look at the differences between the studies can help you evaluate whether or not you should drink coffee – and how much you should drink?

The Duke University Study

The headlines in January 2008 read “Cutting Caffeine May Help Control Diabetes“. Dr. James Lane, a psychologist at Duke University, and his team of researchers worked with a group of ten people with Type 2 diabetes. This was the second study on the effects of caffeine on blood glucose levels done by Lane’s group. Both studied the effects of caffeine on glucose levels over the course of the day. In this second study, each participant was implanted with a glucose meter to constantly monitor their blood glucose levels over the course of 72 hours.

On each day, half the group was given caffeine tablets that contained the equivalent caffeine of two cups of coffee and the other half were given a placebo. The groups were alternated, so that each participant received caffeine on some days and placebo on others. The glucose monitors showed that on the days that participants took caffeine, their glucose levels were consistently higher throughout the day than on the days that they took placebos, even though their meal and exercise patterns were identical. Not only that, the effect appeared to be cumulative – the difference between placebo and caffeine glucose levels were far greater after dinner than they were after breakfast.

As a result of this study, Lane is suggesting that those diagnosed with Type 2 should cut out the coffee, or switch to decaffeinated to help them control their blood glucose levels.

Other Studies


Between 2003 and 2008, multiple studies have found a strong link between coffee consumption and reduced risk of Type 2 diabetes. These studies were long-term studies that involved correlating coffee drinking habits with later development of Type 2 diabetes in various populations. The samples studied were very large – from 900 to over 50,000 participants. Rather than studying the physical effects of coffee or caffeine on each individual, researchers divided groups according to how much coffee they reported drinking on a regular basis, and then compared the number of new diagnoses of Type 2 diabetes among each of the groups. Nearly every study has shown that those who drink four or more cups of coffee per day are far less likely to develop Type 2 diabetes than those who drink less than one cup of coffee per day. Some of the studies found that those who drink decaf coffee also are less likely to develop Type 2 diabetes. All of them found that those who drink other caffeinated beverages show no reduction in Type 2 diabetes risk at all.

The Differences

The Duke University studies tested the effects of caffeine, not coffee. Many of the other studies have found that the positive effects of coffee are still there even when the coffee was decaf. It appears that the benefits may be due to something other than caffeine.

The Duke University studies were short term and focused on the immediate effects of consuming caffeine while the other studies have focused on the long term effects of regular coffee consumption. Interestingly, there are similarly disparate results between the immediate (and temporary) effects of coffee on blood pressure and the long term effects of coffee on hypertension. In the short term, coffee raises blood pressure. In the long term, regular coffee consumption appears to reduce the risk of developing chronic hypertension.

The Duke University studies measured blood glucose levels in people who had already been diagnosed with Type 2 diabetes but were not using insulin to control blood sugar. The results showed that caffeine consumption at mealtimes affects the way that the body converts food into glucose, possibly by decreasing insulin sensitivity.

The Duke University studies focused on those who already were diagnosed with Type 2 diabetes. The other studies focused on those without a prior diagnosis of Type 2 diabetes and measured the risk of developing the condition.

The Conclusions

Obviously, further research is needed before any health agency makes an official proclamation, but there are promising avenues of study. The current research suggests that drinking coffee – not caffeine consumption – can help reduce the risk of developing Type 2 diabetes in later years. It also suggests that those who are having trouble controlling their blood sugar levels should be aware of the effect that caffeine has on food metabolism, and consider cutting back on caffeine consumption.