Not too long ago, coffee drinking was considered a bad habit and many people avoided it for health reasons. But now, as with chocolate and wine, the pendulum has swung so far in the other direction that we have to remind readers that moderation is still a good idea.
Coffee, the world’s most popular beverage after water and tea, used to be blamed for everything from high blood pressure and high cholesterol (and thus heart disease) to pancreatic cancer, fibrocystic breasts and bone loss. But early research linking coffee or caffeine to health problems has almost always been refuted by better studies. In recent years, most research has suggested that coffee actually has health benefits.
How can coffee be healthful?
Like all plant foods, coffee beans contain many naturally occurring chemicals—more than 1,000 have been identified so far, many formed during the roasting process. Some are potentially harmful for coffee drinkers, while others are potentially healthful, according to lab studies. Many of the beneficial substances are polyphenols that are antioxidants; these contribute to the bitter and acidic taste of the beverage. In fact, coffee is the No.1 source of antioxidants in the U.S. and many other countries, largely because we drink so much of it.
For most people, coffee means caffeine, which is one of the most studied substances in food. Caffeine is a natural pesticide that helps protect coffee plants from predators. Brewed coffee typically contains anywhere from 60 to 120 milligrams of caffeine in six ounces. Caffeine is a mild psychoactive substance that stimulates the central nervous system. Thus, it improves reaction time, mental acuity, alertness and mood; wards off drowsiness; and helps people wake up and feel better in the morning. So it’s no surprise that a recent Australian study of long-distance truck drivers, published in BMJ, found that caffeine greatly reduced the risk of crashes.
What’s more, caffeine is classified as an “ergogenic aid” because it can improve some aspects of athletic performance. It also enhances the analgesic effect of pain relievers, which is why it’s in some over-the-counter formulations.
Coffee's potential health benefits
Every month or two another study on coffee comes out. Most research has focused on regular coffee, but some has included decaf. Here’s a sampling of recent findings:
Diabetes. Research, including two large studies in the American Journal of Clinical Nutrition in 2012 and 2013, has fairly consistently linked long-term coffee consumption (regular or decaf) to a reduced risk of type 2 diabetes. Some of coffee’s polyphenols may enhance insulin sensitivity and slow the release of glucose into the bloodstream. Most studies on people who already have diabetes have not found a benefit from coffee, however.
Heart disease. Compounds in coffee have positive and negative effects on coronary risk. Overall, coffee does not affect the risk of heart attacks (or strokes), according to a large German study last year as well as previous research. One way coffee may be good for the heart is by reducing the risk of diabetes. One way it can be bad is if it is unfiltered and raises blood cholesterol.
Blood pressure and stroke. There has long been a concern about caffeine’s effect on blood pressure. However, a 2011 review of studies concluded that it’s okay for people with controlled hypertension to drink caffeinated coffee. The studies on the acute effects found that in people with hypertension who had abstained from caffeine for 9 to 48 hours, two cups of coffee raised blood pressure (7 points, on average) for up to three hours. But in studies lasting two weeks, daily coffee intake did not increase blood pressure, probably because tolerance to caffeine develops in about a week. And longer observational studies in the review found no link between habitual coffee consumption and the risk of cardiovascular disease.
Even better news, a Swedish analysis published in the American Journal of Epidemiology in 2011 found that moderate coffee consumption was associated with a modest reduction in stroke risk. Other studies have also shown this.
Colon cancer. An analysis from the large NIH-AARP Diet and Health Study last year found that people who drank at least four cups of coffee (regular or decaf) a day were 15 percent less likely to develop colon cancer than nondrinkers. Previous studies have been inconsistent; different coffee types and methods of preparation may have different effects on cancer risk.
Prostate cancer. A British study published in the Nutrition Journallast year found a reduced risk of aggressive prostate cancer in coffee drinkers, though the overall risk for prostate cancer was not affected. That confirms the conclusions of a large 2011 study in the Journal of the National Cancer Institute, which found that men who regularly consumed the most coffee (including decaf) had a 60 percent lower risk of advanced or lethal prostate cancer than nondrinkers. Even drinking one to three cups per day was linked to a 30 percent lower risk. This potential benefit is “biologically plausible,” according to the Harvard researchers, since coffee improves blood sugar control, has antiinflammatory and antioxidant effects and affects sex hormone levels, all of which play a role in prostate cancer progression.
Endometrial cancer. In 2011 two large studies of women linked coffee to a decreased risk of endometrial cancer. This was especially true of obese women, who are at increased risk for the disease.
Parkinson’s disease. Many observational studies have suggested that coffee helps protect against Parkinson’s, according to a review paper in Experimental Neurobiology last year. It noted that caffeine appears to have neuroprotective effects, though this may depend on a genetic variable involved in caffeine metabolism.
Depression. Women who drank two to three cups of regular coffee a day over a 10-year period were 15 percent less likely to develop depression than those who drank little or no coffee, according to a 2011 analysis from the Nurses’ Health Study. The authors theorized that coffee can positively affect serotonin and other brain chemicals.
Cognitive decline. In a study in the Journal of Alzheimer’s Disease in 2011, older women (but not men) who drank coffee had a reduced rate of cognitive decline over an eight-year period. Another paper in the same journal last year linked higher levels of caffeine in the blood to reduced progression from mild cognitive impairment to dementia in people over 65.
Liver disease. Several recent studies suggest that regular coffee may protect against the development or progression of non-alcoholic fatty liver disease.
Life expectancy. People who drank at least two cups of coffee (regular or decaf) a day were 10 to 15 percent less likely to die over a 14-year period than nondrinkers, according to a large study in the New England Journal of Medicine in 2012. Smoking and other factors that influence health and longevity were taken into account. Reductions were seen in deaths from diabetes, heart and respiratory disease, strokes, infections and accidents.
Bottom line: There’s no health reason to deprive yourself of coffee if you like the lift it gives and the sociability it affords, unless it affects you adversely. On the other hand, we can’t recommend that anyone start drinking coffee for its potential benefits, since most are still too uncertain. Notably, all the long-term studies have been observational, so they do not prove cause and effect. Keep in mind that tea also contains an array of potentially beneficial compounds and has been linked to many health benefits.
It is easy to see why some people worry about coffee. A stimulant, it can cause jitters and insomnia, stomach upset and heartburn. It can also boost heart rate temporarily, which is why people with certain heart problems may be advised to avoid it.