Scientific research may soon help coffee shed some of its image as an unhealthy drink. Or at least that's what the big companies that sell it are hoping it will do.

With tens of millions of cups of coffee jolting Americans awake each day, a bevy of research is under way trying to tease out the health advantages -- and disadvantages -- of the nation's coffee fixation.

Coffee's image took a hit in 1982 when a major study concluded that frequent use increased the risk of pancreatic cancer. Since then, coffee companies have funded more and more research seeking to show the opposite: that coffee may actually have some health benefits.

While studies are backing up some of the health warnings, a growing body of research is suggesting that daily coffee consumption may lower the risk of type 2 diabetes.

According to Lenore Arab, PhD, a nutritional epidemiologist at UCLA, other studies suggest less conclusively that coffee could help lower the risk of liver cancer, Parkinson's disease, and possibly colon cancer. And Arab says other research suggests high coffee intake by pregnant women can put their children at risk of leukemia.

Arab spoke at the Federation of American Societies of Experimental Biology annual meeting in Washington. He says two major studies, one from Canada and the other from Uruguay, showed a 60 percent to 70 percent increased risk of bladder cancer among regular coffee drinkers.

"Cancer -- the total picture -- is somewhat mixed," Arab says.

"Basically, it's neutral," says Dan Steffen, a scientific public relations official with Kraft Foods.

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Diabetes Benefits

But coffee companies are most excited about evidence suggesting coffee could help prevent diabetes.

Rob M. van Dam, PhD, a Harvard researcher, says his 2005 analysis of eight major studies concluded that adults who consume six to seven cups of coffee per day lower their risk of diabetes by one-third over those who drink two cups per day.

Van Dam says a study last year showed two or three cups per day lowered women's diabetes risk by 13 percent. Four or more cups per day cut the risk by more than 40 percent.

At least seven other studies suggest similar benefits, says van Dam.

The findings are puzzling to researchers because several of caffeine's individual components, including caffeine, raise cholesterol and lower sugar metabolism. That should make them worse for diabetes, not better.

"We're not talking about caffeine," van Dam says. "It really seems to be the coffee, rather than the caffeine."

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Stronger Data Needed

Van Dam and other researchers warn that almost all of their evidence comes from population- based studies, not the kind of controlled, randomized clinical trials that can better determine true cause-and-effect relationships.

Coffee has thousands of components, most of which are not well studied. It's not even clear that European studies on the benefits of a few daily cups of coffee offer any good conclusions for America's legions of consumers.

"What the heck is a cup? Is it a Starbuck's 20-ouncer, or is it a 5-ounce teacup?" says James Coughlin, PhD, a private toxicology consultant and one-time coffee industry scientist.

Van Dam also stresses that he does not recommend coffee as a diabetes prevention aid. "If you want to lower the risk of diabetes, you'd better focus on whole-grain consumption, physical activity, and weight loss," he says.

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This article was reviewed by Louise Chang, MD.

SOURCES: Dan Steffen, PhD, Scientific and Regulatory Affairs, Kraft Foods. Lenore Arab, PhD, nutritional epidemiologist, David Geffen School of Medicine, UCLA. Rob M. van Dam, PhD, research scientist, department of nutrition, Harvard School of Public Health. James Coughlin, PhD, Coughlin & Associates.