In short term studies, these finding may be contradicted, suggesting that coffee with caffeine may reduce the body's sensitivity to insulin and therefore pose additional problems. However, in the Harvard study, over 100,000 men and women were followed for almost 20 years. Hu indicated that the next step would be to try and replicate the long term study's results. The question being of course, how many of us have 20 years to sit around and wait to see if we should be drinking coffee.
Coffee is Good for Men and Women
The more coffee the men and women drank, the more it seemed to help prevent diabetes. The findings held true even after accounting for other risk factors linked to diabetes, including age and weight.
- 1 to 3 cups of coffee a day dropped the risk of diabetes in men by 7%.
- 4-5 cups a day cut the risk of diabetes by 30%.
- 6 or more cups of coffee a day dropped the risk of diabetes by more than 50%.
- No effect on diabetes prevention was seen for women who drank 1 to 3 cups a day.
- Four cups or more a day reduced their risk of diabetes by about 30%.
- 6 cups did not seem to be any better than four cups.
Decaf or Regular Coffee?
Caffeine might be coffee's best-known ingredient, but it's not the only one, Hu notes. Coffee houses dozens of other substances that could affect disease risk. There's magnesium, niacin, potassium, and even such antioxidants as tocopherol.
Hu's team reasoned they could tease out the effects of caffeine on diabetes prevention by also looking at tea and decaf coffee.
"Decaf coffee has the same amount of these other substances, but less caffeine," Hu says. "Tea has other substances and is relatively low in caffeine."
Four or more cups of decaf coffee a day was associated with a modest effect on diabetes prevention. But the findings could have been due to chance, Hu says.
Tea had no impact on diabetes prevention, the researchers found.
The researchers then looked at total caffeine intake from coffee, sodas, and other foods, and found it, too, appeared to help prevent diabetes. Men and women who consumed the most caffeine were about 25% less likely to develop diabetes compared with those who consumed the least.
I'm a believer in coffee
The new findings on coffee have made a believer out of at least one former skeptic, and a key one at that: Terry E. Graham, PhD, who performed one of the studies showing caffeine reduces the body's ability to handle blood sugar.
"When the Dutch coffee study came out, I was shocked," says Graham, chairman of human biology & nutritional sciences at the University of Guelph in Guelph, Canada. "But now, with this second study that shows the same thing, you start to believe it."
The Harvard study is more thorough, he says, with more accurate data about the participants' coffee habits over 10 to 15 years. "Plus, they evaluated tea and decaf coffee, which the first study didn't."
Some clues into why the short-term and long-term studies arrive at such different results might come soon, he says. Vanderbilt University researchers who are studying compounds produced when coffee beans are roasted appear to have homed in on some with disease-fighting properties.
In the meantime, Hu says he is not yet ready to recommend coffee to help prevent diabetes.
"We still need more study," he says. "But it's intriguing. And it's not detrimental -- one thing coffee lovers don't have to worry about."
Gourmet coffee lovers rejoice