TUESDAY, Nov. 22 (HealthDay News) -- Women who drink moderate to high amounts of coffee may reduce their risk for endometrial cancer, new research reveals.

The finding stems from what investigators call the largest study to date to explore the impact of coffee and tea on the risk of endometrial cancer, which is cancer that originates in the lining of the uterus.

The study found that women who consume four or more cups of caffeinated coffee per day appear to lower their risk for endometrial cancer by 25 percent, relative to women who drink less than one cup a day.

Drinking fewer than four cups a day did not appear to offer any preventative benefit, however. Nor did drinking tea.

But there was some indication that decaffeinated coffee might be helpful, as drinking two or more cups of decaf daily was linked (although only tentatively) to a 22 percent drop in endometrial cancer risk.

Still, "this study does not prove cause and effect," cautioned study co-author Dr. Edward Giovannucci, a professor of nutrition and epidemiology at the Harvard School of Public Health. "But this observation has been suggested previously, and there's strong reason now to believe that this association is real."

Giovannucci pointed to a number of potential explanations. "One is that women with higher levels of estrogen and insulin are at a higher risk for endometrial cancer, and coffee seems to reduce levels of both," he said. "Also women with diabetes also face a much higher risk, and coffee has been associated with a lower risk for diabetes. So there are several factors that could be involved.

"We also think that any risk reduction is probably related to something other than caffeine," he added. "Because coffee is a fairly complex beverage with literally thousands of compounds. In fact, coffee has one of the highest concentrations of antioxidants, and any number of those could have a beneficial aspect."

The findings appear in the current issue of Cancer Epidemiology, Biomarkers & Prevention.

The authors point out that endometrial cancer is currently the most prevalent gynecologic cancer among American women.

In addition to routine exercise and weight maintenance, researchers have theorized that certain aspects of diet might play a role in endometrial cancer prevention.

Coffee has been highlighted as a possible game-changer, given its impact on circulating hormone levels. The authors note that recent studies from Japan and Sweden support this conjecture.

To further explore coffee's potential, the research team analyzed data that had previously been collected by the Nurses' Health Study .

Initially launched in 1976, the study as a whole involved women between the ages of 30 and 55, residing in 11 different states.

The authors focused on the coffee-drinking habits of roughly 67,500 study participants, conducting surveys at two-year intervals to track endometrial cancer incidence over 26 years. Dietary habits were assessed in surveys that were completed once every four years between 1980 and 2002.

The team observed 672 cases of endometrial cancer.

After accounting for a range of factors (such as smoking habits, body mass index and alcohol consumption) the authors found that four or more cups of caffeinated coffee was "significantly" associated with a 25 percent drop in endometrial cancer risk.

That said, the team hesitated to endorse high levels of coffee consumption, noting that the apparent benefit could be negated among those who routinely add cream and sugar to their cup of joe.

Dr. Janice Dutcher, director of immunotherapy at St Luke's Roosevelt Hospital Center and Beth Israel Medical Center in New York City, suggested the findings should not been interpreted as anything more than an "interesting hypothesis."

"I'm skeptical," she said. "My skepticism comes from the fact that a variety of things have been associated with cancer at one point, and then not associated with cancer later on. Twenty years ago it was thought coffee was the cause of pancreatic cancer. And to isolate one dietary factor from all the other things that people take in is very complicated. So while I'm sure this is a carefully done study with good methodology, I would be very careful about drawing any conclusions."

More information

For more on endometrial cancer, visit the U.S. National Institutes of Health.