Feature Archive

Coffee and Your Health

Say it's so, Joe: The potential health benefits -- and drawbacks -- of coffee.

By Neil Osterweil
WebMD Feature

Reviewed by Jonathan L. Gelfand, MD

Coffee may taste good and get you going in the morning, but what will it do for your health?

A growing body of research shows that coffee drinkers, compared to nondrinkers, are:

"There is certainly much more good news than bad news, in terms of coffee and health," says Frank Hu, MD, MPH, PhD, nutrition and epidemiology professor at the Harvard School of Public Health.

But (you knew there would be a "but," didn't you?) coffee isn't proven to prevent those conditions.

Researchers don't ask people to drink or skip coffee for the sake of science. Instead, they ask them about their coffee habits. Those studies can't show cause and effect. It's possible that coffee drinkers have other advantages, such as better diets, more exercise, or protective genes.

So there isn't solid proof. But there are signs of potential health perks -- and a few cautions.

If you're like the average American, who downed 416 8-ounce cups of coffee in 2009 (by the World Resources Institute's estimates), you might want to know what all that java is doing for you, or to you.

Here is a condition-by-condition look at the research.

Type 2 Diabetes

Hu calls the data on coffee and type 2 diabetes "pretty solid," based on more than 15 published studies.

"The vast majority of those studies have shown a benefit of coffee on the prevention of diabetes. And now there is also evidence that decaffeinated coffee may have the same benefit as regular coffee," Hu tells WebMD.

In 2005, Hu's team reviewed nine studies on coffee and type 2 diabetes. Of more than 193,000 people, those who said they drank more than six or seven cups daily were 35% less likely to have type 2 diabetes than people who drank fewer than two cups daily. There was a smaller perk -- a 28% lower risk -- for people who drank 4-6 cups a day. The findings held regardless of sex, weight, or geographic location (U.S. or Europe).

More recently, Australian researchers looked at 18 studies of nearly 458,000 people. They found a 7% drop in the odds of having type 2 diabetes for every additional cup of coffee drunk daily. There were similar risk reductions for decaf coffee drinkers and tea drinkers. But the researchers cautioned that data from some of the smaller studies they reviewed may be less reliable. So it's possible that they overestimated the strength of the link between heavy coffee drinking and diabetes.

How might coffee keep diabetes at bay?

"It's the whole package," Hu says. He points to antioxidants -- nutrients that help prevent tissue damage caused by molecules called oxygen-free radicals. "We know that coffee has a very strong antioxidant capacity," Hu says.

Coffee also contains minerals such as magnesium and chromium, which help the body use the hormone insulin, which controls blood sugar (glucose). In type 2 diabetes, the body loses its ability to use insulin and regulate blood sugar effectively.

It's probably not the caffeine, though. Based on studies of decaf coffee, "I think we can safely say that the benefits are not likely to be due to caffeine," Hu says.

Hold the Caffeine?

The fact that coffee contains good stuff does not necessarily follow mean it's good for us, says James D. Lane, PhD, professor of medical psychology and behavioral medicine at Duke University Medical Center in Durham, N.C.

"It has not really been shown that coffee drinking leads to an increase in antioxidants in the body," Lane tells WebMD. "We know that there are antioxidants in large quantities in coffee itself, especially when it's freshly brewed, but we don't know whether those antioxidants appear in the bloodstream and in the body when the person drinks it. Those studies have not been done."