More than just caffeine
One after another, foods that were once cast as dietary bad guys have seen their images rehabilitated. Nuts, eggs, avocados, even chocolate have been welcomed back into the kitchen as new research has dispelled worries and even pointed to potential health benefits.
The latest candidate for a makeover is coffee.
In the 1970s and 1980s, coffee was blamed for a variety of ills, from high blood pressure to cancer. “The focus of early research was almost always on finding fault,” says Harvard Medical School epidemiologist Alan Leviton. “People tended to think of coffee as a vice, so the bias was that there had to be something wrong with it.”
But very few of those worries have been born out by research, Leviton says. “And now we’re starting to see evidence of some intriguing benefits associated with coffee.”
Findings published over the last five years suggest that coffee may protect against gallstones, diabetes and even Parkinson’s disease.
Interest in the link between coffee and gallstone disease first began to percolate in the early 1990s, when laboratory research demonstrated that caffeine can reduce the size of these small crystallized stones, and perhaps prevent them from forming in the first place. “What we didn’t know was whether coffee drinkers out in the real world would get any benefit,” says nutrition researcher Michael Leitzmann.
In findings published in 1999, he and colleagues at the Harvard School of Public Health looked at data from 46,008 men who are being followed in the Health Professionals Follow-up Study. Coffee drinkers, they found, were significantly less likely to develop gallstones than men who didn’t drink the beverage. In 2002, the same team looked at 80,898 women who are part of the Women’s Health study. Among women, too, coffee drinkers tended to have less risk of developing gallstones.
The evidence was especially persuasive because the effect was dose-dependent. “The more coffee people drank, the lower their risk of developing gallstones,” Leitzmann says. The risk fell 13% among those who drank one cup a day, 21% for people who drank two to three cups, and 33% for people who drank four or more cups a day.
Decaffeinated coffee didn’t protect against gallstones, however, suggesting that the active component may be caffeine.
Caffeine also appears to be responsible for another potential benefit for coffee drinkers -- a lowered risk of Parkinson’s disease.
In a 2000 study of 8,004 men whose health and diets have been tracked for 30 years, researchers at the Department of Veterans Affairs in Honolulu found that coffee drinkers significantly reduced their odds of developing Parkinson’s, the debilitating disease that affects the brain and nervous system. In 2001, Harvard School of Public Health researchers published similar findings from studies that included more than 130,000 men and women.
“Men who reported drinking the most coffee had the lowest risk of developing Parkinson’s disease,” says epidemiologist Alberto Ascherio, who led the study. Women also benefited, but only from moderate coffee consumption, one to three cups a day.
Researchers don’t understand why coffee appears to protect against Parkinson’s -- although, again, caffeine seems to be responsible. “When we looked at men who drank decaffeinated coffee, we didn’t find a lower risk,” Ascherio says. “But when we looked at caffeine from other sources, such as tea or caffeinated soft drinks, we did see a protective effect.”
Scientists are just beginning to explore how caffeine and Parkinson’s may be linked. The disease results when levels of the brain chemical dopamine fall, interrupting nerve signals from the brain to muscles. At the Neurosciences Institute in La Jolla, researchers Frederick S. Jones and Anthony H. Stonehouse reported this year that caffeine increases the expression of dopamine receptors in the brain.
One of the most surprising benefits associated with drinking coffee is protection against Type 2 diabetes.
In a study of 17,111 men and women published in the British medical journal the Lancet in 2002, Dutch researchers reported that people who drank at least seven cups of coffee a day were half as likely as those who drank two or fewer cups to develop diabetes. Two other studies of large groups have confirmed the good news.
Analyzing data from more than 125,000 men and women, Harvard School of Public Health researchers found that men who drank six or more cups of coffee daily were half as likely to develop diabetes. Women who drank six or more cups a day cut their risk by 30%. A Swedish study published in 2004, which followed 1,361 women over 18 years, found that the more coffee the women drank, the lower their odds of developing diabetes.
Researchers suspect that substances other than caffeine explain why coffee is associated with lowered risk of diabetes. In fact, caffeine in short-term studies decreases insulin sensitivity, which should theoretically worsen the condition, not protect against it. But coffee is rich in many other substances that are biologically active, some of which are only beginning to be investigated.
“Caffeine has received most of the research attention, but it is only one of hundreds of substances found in coffee,” says coffee chemist Tomas de Paulis, a researcher at Vanderbilt University’s Institute for Coffee Studies, which receives funding from coffee manufacturers.
He and his colleagues are investigating substances in coffee called quinides, which increase the capacity of the liver to use glucose. That, in theory, should improve blood sugar control in diabetics. Unlike caffeine, these substances may be unique to coffee, created during the process of roasting coffee beans.
Coffee, like tea, is also turning out to be a plentiful source of antioxidants, which may protect against the damage caused by unstable free-radical oxygen molecules. In an analysis published early this year that looked at the diets of 2,672 Norwegians -- among the world’s most avid coffee drinkers -- coffee was found to be the biggest contributor of antioxidants on the menu.
The antioxidants in coffee may also explain preliminary findings that suggest that coffee drinking may lower the risk of oral cancer and heart disease. In addition, coffee is a good source of the mineral magnesium, which could partly explain why it seems to protect against diabetes. Diabetics often have abnormally low levels of the mineral.
Guilt by association
Why, then, has coffee had a bad reputation for so long? One reason is guilt by association. In early studies, coffee drinkers often tended to be smokers and alcohol drinkers, says Leitzmann, who is now a researcher at the National Cancer Institute. As a result, some early studies blamed higher cancer rates on coffee.
“We now know that those risks are really associated with smoking or excessive alcohol consumption, not drinking coffee,” Leitzmann says.
In other instances, lack of an understanding of biological mechanisms led to unwarranted concerns. Early studies showed that pregnant women who reported drinking more coffee were more likely to miscarry, for example. Coffee was blamed for miscarriages. Researchers now know that in early pregnancy, many women find the taste and smell of coffee unpleasant, as a result of hormonal changes. The healthier the pregnancy, the stronger those signals, and the less coffee women tend to drink.
“When the placenta is in place and the pregnancy is a healthy one, most women get a strong pregnancy signal, so they drink less coffee. Women who don’t have as good an implantation and are therefore at increased risk of miscarriage have less of a pregnancy signal, and so they tend to go on drinking their usual amount of coffee,” Leviton explains. “Drinking coffee doesn’t cause the miscarriages. It’s just a marker for how weak the pregnancy signal is.”
Many of the early worries over coffee surfaced in very small studies that lacked statistical legitimacy and may have been biased by a tendency to assume there were dangers to drinking coffee, Leviton says.
The latest evidence comes from very large studies that involve tens of thousands of people and whose findings are generally considered to be more reliable. A few small studies suggested increased risk of some cancers, for example, but when scientists in 2000 pooled the available data from many studies, they found no statistical link between the disease and coffee drinking.
A few worries persist. Caffeine can aggravate arrhythmias, or irregular heartbeats, so cardiologists sometimes advise people with such conditions to switch to decaf. Insomnia sufferers are also typically advised to give up caffeinated coffee, especially late in the day and evening. Because caffeine can make its way into breast milk, the American Academy of Pediatrics recommends that nursing mothers drink decaf coffee or other non-caffeinated beverages.
Caffeine in coffee also raises blood pressure temporarily, so people with hypertension might do well to avoid it. But several extensive studies have shown that coffee drinkers are no more likely than nondrinkers to suffer chronic high blood pressure -- evidence that coffee doesn’t cause hypertension.
“The real news is that drinking coffee poses no danger to most people,” Leviton says. “If coffee turns out to have benefits, as some of the new evidence suggests, all the better.”
For now, the findings are preliminary enough that even the researchers who have turned up benefits say it’s too early to recommend that people who don’t drink coffee should start.
“We need to know more about the mechanisms at work in conditions like Parkinson’s or diabetes before we can feel comfortable making recommendations,” says Peter Martin, who directs the Institute for Coffee Studies at Vanderbilt.
Ultimately, Martin says, the latest research is more likely to yield new drugs based on compounds found in coffee than recommendations for people to drink the beverage. Several pharmaceutical companies are already looking at developing drugs based on components found in coffee beans.
Still, for the more than 166 million Americans who drink coffee -- up more than 5 million from 2002, according to figures released by the National Coffee Assn. -- the new findings offer one more reason to love a good strong cup of java.