Regular coffee, of course, also contains caffeine. Caffeine can raise blood pressure, as well as blood levels of the fight-or-flight chemical epinephrine (also called adrenaline), Lane says.

Heart Disease and Stroke

Coffee may counter several risk factors for heart attack and stroke.

First, there's the potential effect on type 2 diabetes risk. Type 2 diabetes makes heart disease and stroke more likely.

Besides that, coffee has been linked to lower risks for heart rhythm disturbances (another heart attack and stroke risk factor) in men and women, and lower risk for strokes in women.

In a study of about 130,000 Kaiser Permanente health plan members, people who reported drinking 1-3 cups of coffee per day were 20% less likely to be hospitalized for abnormal heart rhythms (arrhythmias) than nondrinkers, regardless of other risk factors.

And, for women, coffee may mean a lower risk of stroke.

In 2009, a study of 83,700 nurses enrolled in the long-term Nurses' Health Study showed a 20% lower risk of stroke in those who reported drinking two or more cups of coffee daily, compared to women who drank less coffee or none at all. That pattern held regardless of whether the women had high blood pressure, high cholesterol levels, and type 2 diabetes.

Parkinson's and Alzheimer's Diseases

"For Parkinson's disease, the data have always been very consistent: higher consumption of coffee is associated with decreased risk of Parkinson's," Hu tells WebMD. That seems to be due to caffeine, though exactly how that works isn't clear, Hu notes.

Coffee has also been linked to lower risk of dementia, including Alzheimer's disease. A 2009 study from Finland and Sweden showed that, out of 1,400 people followed for about 20 years, those who reported drinking 3-5 cups of coffee daily were 65% less likely to develop dementia and Alzheimer's disease, compared with nondrinkers or occasional coffee drinkers.

Cancer

The evidence of a cancer protection effect of coffee is weaker than that for type 2 diabetes. But "for liver cancer, I think that the data are very consistent," Hu says.

"All of the studies have shown that high coffee consumption is associated with decreased risk of liver cirrhosis and liver cancer," he says. That's a "very interesting finding," Hu says, but again, it's not clear how it might work. 

Again, this research shows a possible association, but like most studies on coffee and health, does not show cause and effect.

Pregnancy

In August 2010, the American College of Obstetricians and Gynecologists (ACOG) stated that moderate caffeine drinking – less than 200 mg per day, or about the amount in 12 ounces of coffee – doesn't appear to have any major effects on causing miscarriage, premature delivery, or fetal growth.

But the effects of larger caffeine doses are unknown, and other research shows that pregnant women who drink many cups of coffee daily may be at greater risk for miscarriage than non-drinkers or moderate drinkers. Again, it's not clear whether the coffee was responsible for that.

Calories, Heartburn, and Urine

You won't break your calorie budget on coffee -- until you start adding the trimmings.

According to the web site myfoodapedia.gov -- part of the U.S. Department of Agriculture's Center for Nutrition Policy and Promotion -- a 6-ounce cup of black coffee contains just 7 calories. Add some half & half and you'll get 46 calories. If you favor a liquid nondairy creamer, that will set you back 48 calories. A teaspoon of sugar will add about 23 calories.

Drink a lot of coffee and you may head to the bathroom more often. Caffeine is a mild diuretic -– that is, it makes you urinate more than you would without it. Decaffeinated coffee has about the same effect on urine production as water.

Both regular and decaffeinated coffee contain acids that can make heartburn worse.

SOURCES:

Frank Hu, MD, MPH, PhD, professor of nutrition and epidemiology, Harvard School of Public Health.

James D. Lane, PhD, professor of medical psychology and behavioral medicine, Duke University Medical Center, Durham, N.C.

Barbara Shukitt-Hale, PhD, research psychologist, USDA Human Nutrition Research Center on Aging, Boston.

World Resources Institute.

van Dam, R. Journal of the American Medical Association, July 6, 2005; vol 94: pp 97-104.

Huxley, R.. Archives of Internal Medicine, Dec. 14-28, 2009; vol 169: pp 2053-2063.

American Heart Association Nutrition, Physical Activity and Metabolism/50th Cardiovascular Disease Epidemiology and Prevention conference, San Francisco, March 2-5, 2010.

Lopez-Garcia, E. Circulation, Feb. 16, 2009; advance online edition.

Marjo, H. Journal of Alzheimer's Disease, January 2009; pp 85-91.

Galeone, C. Cancer Epidemiology, Biomarkers & Prevention, July 2010; published ahead of print.

American Association for Cancer Research International Conference on Frontiers in Cancer Prevention Research, Houston, Dec. 6-9, 2009.

American College of Obstetrics and Gynecology Committee on Obstetric Practice, Obstetrics & Gynecology. August 2010, vol 116: pp 467-468.

Center for Nutrition Policy and Promotion, U.S. Department of Agriculture: Myfoodapedia.gov

Reviewed on August 29, 2011

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