Coffee drinkers, rejoice! The heavenly brew, once deemed harmful to health, is turning out to be, if not quite a health food, at least a low-risk drink, and in many ways a beneficial one. It could protect against diabetes, liver cancer, cirrhosis and Parkinson's disease.
What happened? Lots of new research, and the recognition that older, negative studies often failed to tease apart the effects of coffee and those of smoking because so many coffee drinkers were also smokers.
"Coffee was seen as very unhealthy," said Rob van Dam, a coffee researcher and epidemiologist at the Harvard School of Public Health. "Now we have a more balanced view. We're not telling people to drink it for health. But it is a good beverage choice."
As you digest the news on coffee, keep in mind that coffee and caffeine are not the same thing. In fact, "they are vastly different," said coffee researcher Terry Graham, chairman of Human Health and Nutritional Sciences at the University of Guelph in Ontario, Canada. One can be good for you; the other, less so.
"Coffee is a complex beverage with hundreds, if not thousands, of bioactive ingredients," he said. "A cup of coffee is 2% caffeine, 98% other stuff."
Before we rhapsodize further, a few caveats:
Caffeine -- whether in coffee, tea, soft drinks or pills -- can make you jittery and anxious and, in some people, can trigger insomnia. Data are mixed on whether pregnant women who consume caffeine are more likely to miscarry. In general, 200 milligrams a day -- the amount in one normal-sized cup of coffee -- is believed safe for pregnant women, said Van Dam.
For people with hard-to-control hypertension, a sudden, big dose of caffeine may boost blood pressure because caffeine constricts blood vessels. But decaf is fine in that respect. And even caffeinated coffee doesn't increase blood pressure much once you drink it for a week or so, said Van Dam. In fact, the caffeine in coffee seems to have less of an effect on blood pressure than the caffeine in colas because there are so many other substances in coffee that have the opposite effect physiologically from caffeine.
One final caveat: The new research heralding coffee's health benefits is not perfect. Most of the studies are observational; that is, they followed people over time and correlated health outcomes with coffee drinking -- based on people's recollections of how much coffee they consumed. The studies don't prove that coffee was the cause of improved health outcomes. Still, the sheer volume of the research, and the fact that the conclusions line up so neatly, make it reasonably credible, researchers say.
Diabetes: Twenty studies worldwide show that coffee, both regular and decaf, lowers the risk for Type 2 diabetes, in some studies by as much as 50%. Researchers say that is probably because chlorogenic acid, one of the many ingredients in coffee, slows uptake of glucose (sugar) from the intestines. (Excess sugar in the blood is a hallmark of diabetes.) Chlorogenic acid may also stimulate GLP-1, a chemical that boosts insulin, the hormone that escorts sugar from the blood into cells. Yet another ingredient, trigonelline, a precursor to vitamin B3, may help slow glucose absorption.
Heart disease and stroke: Recent studies suggest that frequent coffee consumption does not increase the risk of either condition. In fact, coffee might -- repeat, might -- slightly reduce the risk of stroke. A study published in March in the journal Circulation looked at data on more than 83,000 women older than 24. It showed that those who drank two to three cups of coffee a day had a 19% lower risk of stroke than those who drank almost none. A Finnish study found similar results for men.
For cardiovascular diseases other than stroke, there doesn't appear to be a preventive benefit from drinking coffee, but there is also no clearly documented harm; the studies looked at the effect of drinking up to six cups of regular coffee a day.
Cancer: Coffee research has come up empty here -- with one big exception: liver cancer. Research consistently shows a drop in liver cancer risk with coffee consumption, and there is some, albeit weaker, evidence that it may lower colon cancer risk as well.
Cirrhosis: Coffee seems to protect the liver against cirrhosis, especially that caused by alcoholism. It's not clear, either for cancer or cirrhosis, whether it's coffee or caffeine that may be protective.