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Caffeine Tied to Blood Sugar Problems

But Don't Be Too Quick to Blame Coffee, Say Researchers
WebMD Health News

Mar. 9, 2005 -- Caffeine can interfere with blood sugar.

But don't shelve your coffee mug just yet. Coffee might not be the culprit. In fact, it may offer some protection against diabetesit may offer some protection against diabetes, say researchers.

Sound confusing? The final verdict isn't in yet. Keep things simple by watching your caffeine intake from all sources. Besides coffee, caffeine is also found in some soft drinks, teas, and chocolate (in smaller amounts).

Caffeine's Buzz Is Common

Just about everyone has at least some caffeine every dayeveryone has at least some caffeine every day, and the numbers are rising for people aged 2-54 years.

Nearly 90% of U.S. adults and 76% of children have caffeine on a daily basis. Soft drinks are the top source for kids; for adults, coffee is No. 1, followed by soft drinks and teas. That's according to a study in January's Journal of the American Dietetic Association.

Checking nutritional labels doesn't always help. Food and drink makers don't have to list the amount of caffeine on the Nutrition Facts label.

Want to start tracking your caffeine? Here's how much caffeine is in popular drinks:

  • Coffee (8 ounces, brewed): about 135 mg
  • Caffeinated tea (8 ounces): about 50 mg
  • Coca-Cola (12 ounces): about 34.5 mg
  • Diet Coke (12 ounces): 46.5 mg

Charting Caffeine's Effects

Participants included 23 white men. Eight were lean, seven were obese and had type 2 diabetes, and eight were obese but did not have diabetes.

They drank up to 5 cups a day of coffee or tea, with two men favoring decaffeinated versions.

The men were then put through a test to determine the men's insulin sensitivity.insulin sensitivity. This is a measure of how well the body is responding to insulin, the hormone that controls blood sugar. If insulin sensitivity is decreased, blood sugar levels can rise. This is a sign that someone either has or is at increased risk of having diabetes.

Prior to the test the men were given either caffeine tablets equal to 2 to 3 cups of coffee or a placebo.

Results showed that caffeine reduced the men's ability to process blood sugar. It also interfered with insulin, the body's hormone that handles blood sugar.

Since exercise has been shown to help blood sugar and insulin, the researchers wanted to see if exercise could offset caffeine's effects.

The men spent 13 weeks on an aerobic exercise program. The men walked or jogged on a treadmill for an hour, five times a week, at moderate intensity. Weight loss wasn't a goal, so they ate more to make up for burned calories.

Exercise didn't make up for caffeine's setbacks. Even when the men worked out, they still had blood sugar and insulin problems while taking caffeine.

Coffee May Not Be to Blame

But what about the studies that show that coffee may protect against type 2 diabetes?

A year ago, The Journal of the American Medical Association reported that people who drank at least 3-4 cups of coffee per day3-4 cups of coffee per day had a nearly 30% lower risk of developing type 2 diabetes.

Here's the catch. In the new study, caffeine came from a pill. But most people get their caffeine from drinks that have other ingredients.

"Coffee contains many other substances besides caffeine, such as potassium, antioxidants, and magnesium," write the researchers, who included Robert Ross, PhD, of Queen's University. Perhaps those other substances are helpful, but that's not certain.

The study appears in the March issue of Diabetes Care.

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