Your morning cup (or cups) of coffee may do more than just jump-start your day.

A new study out of Harvard University suggests that women who habitually drink several cups of coffee per day over the course of years or decades may be less likely than their peers to develop cancer of the endometrium, the lining of their uterus.

The research, published in the journal Cancer Epidemiology, Biomarkers & Prevention, examined data from the Nurses' Health Study, one of the largest and longest-running investigations of factors that influence women's health. Researchers at Harvard University analyzed data on 67,470 women between the ages of 34 and 59 who were followed for about 26 years.

Compared to women who drank little or no coffee, those who averaged four or more cups per day had a 25 percent lower risk of developing endometrial cancer, and those who drank two or three cups per day had a seven percent lower risk. The study, funded by the National Institutes of Health (NIH), doesn't prove that drinking coffee was directly responsible for reducing cancer risk, but the researchers say a cause-and-effect relationship is possible.

Coffee drinking has been shown in previous studies to lower levels of insulin and estrogen, and chronically high levels of both hormones have been linked to endometrial cancer, the researchers point out. But the researchers urge coffee drinkers to hold the cream and sugar, since whatever benefits coffee may have on insulin are almost certainly defeated by the added calories and fat, which could contribute to insulin resistance and weight gain.

Coffee: Preventing more than just cancer?

Dr. Edward Giovannucci, a professor of nutrition and epidemiology at the Harvard School of Public Health in Boston, led the study. The findings, which were published Nov. 27, add to a growing body of evidence that indicates coffee may be actually beneficial when it comes to overall health.

In recent years, studies have linked coffee consumption to a lower risk of liver cancer and prostate cancer, as well as a lower risk of depression, type two diabetes, Parkinson's disease (mainly in men) and cirrhosis of the liver. Research in mice even suggests that coffee may help protect against some of the dementia-related brain changes associated with Alzheimer's disease.

It's not entirely clear how drinking coffee might improve health, but caffeine seems to be only one player, since studies on decaffeinated coffee have shown to have health benefits as well. (In this study, decaffeinated coffee appeared to lower the risk of endometrial cancer, but the researchers had too little data on decaf-only drinkers to reach any reliable conclusions.)

Compounds with antioxidant properties such as flavenoids found in coffee are believed to play a vital role; there are hundreds of different compounds in coffee, many of which are antioxidants that help to prevent cell damage. Surprisingly, coffee contains even more antioxidants than green tea; the researchers looked at tea drinkers in their study, as well, but they found no relationship between tea consumption and risk of developing endometrial cancer.

Hold that espresso

The study has several limitations, so the findings should be interpreted carefully: The researchers relied on biennial diet questionnaires to assess coffee and tea intake, for instance, and although they controlled for a wide range of health factors and behaviors, they can't rule out the possibility that heavy coffee drinkers are culturally and socially different from their peers in ways that could affect cancer risk.

Also, women concerned about cancer risk shouldn't necessarily increase their coffee intake, it should be noted. Although the chronic drinking of caffeinated coffee doesn't appear to have any serious health consequences (such as raising the risk of high blood pressure or hypertension), it can carry some potential side effects, including insomnia, worsened heartburn, heart palpitations, anxiety and irritability.

The "take-home message" of the new study should not be to drink more than four cups of coffee a day, obstetrician/gynecologists say. The most effective way for women to detect or even prevent endometrial cancer is to watch for irregular menstrual bleeding and consult a doctor if they notice anything unusual. Maintaining a healthy body weight by staying physically active is also beneficial for cancer risk as well as a myriad other health reasons.