Interestingly, a study showed that when diabetics had caffeine equivalent to four cups of coffee, their average daily blood sugar levels rose 8 per cent. On the other hand, pre-diabetics (fasting blood sugar higher than 100) had the equivalent to 3 cups of coffee and three hours later, their blood sugar increased by 15 percent and the insulin production by 18 percent. So pre-diabetics may not see a big increase in their blood sugar, but the hyperinsulinemia is getting worse. And as we know, hyperinsulinemia makes interferon ineffective.
Caffeine worsens insulin resistance in prediabetics.
Family Practice News
April 15 2007
WASHINGTON -- Caffeine intake appears to exaggerate post-meal insulin resistance in prediabetic adults who regularly drink several cups of coffee each day, according to preliminary results of a randomized, double-blind, crossover study of 50 individuals.
The results "suggest that caffeine consumption promotes the development of type 2 diabetes in those people who are at greatest risk for this disease," James D. Lane, Ph.D., said at the annual meeting of the Society of Behavioral Medicine.
This is the first time that caffeine's effects on insulin resistance have been measured in habitual coffee drinkers with prediabetes, said Dr. Lane of the department of psychiatry and behavioral medicine at Duke University, Durham, N.C. More than 12 other studies have shown that caffeine administration acutely raises insulin resistance both in healthy, nondiabetic volunteers and in patients with type 2 diabetes.
Other studies have shown that coffee drinking is associated with a significantly reduced risk of type 2 diabetes, but these conclusions have been "based on correlational observations, not controlled, experimental studies," he noted.
In the current study, all participants had prediabetes (average impaired fasting blood glucose level of 111 mg/dL) and drank at least 2 cups of coffee per day, which was confirmed by a 7-day food diary. Each person fasted overnight and did not consume any caffeine, which preserved any tolerance that they had developed from their continued exposure to caffeine.
On the first day of testing, the participants received either 250 mg caffeine or placebo pills and had their fasting blood glucose levels measured. On the second day, they received the opposite of what they had taken on day 1. After 60 minutes, they had their blood glucose levels measured again, and they received a booster dose of 125 mg caffeine or placebo. They also drank a BoostPlus liquid meal replacement shake (75 g carbohydrates, plus fat and protein), which is similar to an oral glucose tolerance test except that it is more like a real meal, Dr. Lane said. Blood samples were drawn during each of the next 3 hours.
The total 375-mg dose of caffeine was equivalent to about 3 cups of brewed coffee, similar to what subjects consumed on average each day (409 mg).
For the first 41 participants with full results available, caffeine increased the 3-hour area under the curve (AUC) for plasma glucose by 15% more than placebo, though the result was not statistically significant. But the 3-hour AUC for plasma insulin was 18% greater with caffeine than with placebo--a significant difference. AUC is the standard method for measuring responses to oral glucose tolerance tests, said Dr. Lane. "'This pattern of results shows that caffeine did increase insulin resistance in these prediabetic subjects."
A normal response to the extra insulin produced with caffeine would have been to reduce the peak glucose level to a point lower than what was seen with placebo. But "'the glucose response was, if anything, a little larger in the caffeine condition," he said. "Given the conditions of our study, we think that this insulin resistance effect occurs every day as these prediabetic individuals and others like them consume caffeinated beverages in the real world."