The study was carried out by Dr James Lane, a psychologist at Duke University Medical Center, in Durham, North Carolina, and colleagues, and is published in the February issue of Diabetes Care.
Other recent studies have shown that in habitual coffee drinkers with type 2 diabetes, caffeine appears to raise glucose and insulin after intakes of standardized carbohydrate loads. Lane and colleagues decided to investigate if this effect manifested after meals in the everyday life of type 2 diabetics and how it might undermine their efforts to manage their condition.
They used small glucose detection devices implanted under the abdominal skin of 10 patients so they could observe the rise and fall of their blood sugar while they went about their normal day for 72 hours, the first time such a thing has been done in relation to caffeine consumption, they said.
The patients had established type 2 diabetes and were regular coffee drinkers who consumed at least two cups everyday. They were also trying to manage their diabetes through a combination of diet, exercise and drugs, but not with extra insulin.
On one day the patients took caffeine capsules equal to about four cups of coffee and on the other day they took identical capsules except they contained a placebo. The study was a double blind crossover study, so neither the patients nor the drug administrators knew which capsules contained the caffeine and which contained the placebo.
The patients all had the same nutrition drink for breakfast but chose their own food for lunch and dinner.
The results showed that on caffeine days, the patients' average daily sugar levels went up by 8 per cent. After meals the blood sugar levels were even higher: 9 per cent after breakfast, 15 per cent after lunch, and 26 per cent after dinner.
Lane said they didn't know how caffeine drove up the glucose levels but they had a couple of ideas.
"It could be that caffeine interferes with the process that moves glucose from the blood and into muscle and other cells in the body where it is used for fuel. It may also be that caffeine triggers the release of adrenaline -- the fight or flight -- hormone that we know can also boost sugar levels," said Lane.
Either way, it appears that caffeine causes blood sugar to rise which is bad news for patients with diabetes, he added.
As more research evidence gathers to support this conclusion, it is likely that official guidelines for how to manage diabetes will advise diabetics to avoid coffee and other drinks that contain caffeine, said the researchers.
As Lane pointed out:
"Coffee is such a common drink in our society that we forget that it contains a very powerful drug: caffeine."
"Our study suggests that one way to lower blood sugar is to simply quit drinking coffee, or any other caffeinated beverages. It may not be easy, but it doesn't cost a dime, and there are no side effects," he added.
The next stage would be to do a study where coffee drinking diabetes patients gave up caffeine to see if this helped them manage their blood sugar levels more easily.
"Caffeine Increases Ambulatory Glucose and Postprandial Responses in Coffee Drinkers With Type 2 Diabetes."
James D. Lane, Mark N. Feinglos, and Richard S. Surwit.
Diabetes Care 31: 221-222.
Published online before print as 10.2337/dc07-1112.
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Source: Diabetes Care article and press release.
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