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.