Filtering Through the Coffee Studies

June 17, 2008— -- Coffee drinking -- even more than six cups a day over the course of almost 20 years -- won't kill you, and may even help you live longer, says a new study.

Researchers from Harvard and the Universidad Autonoma de Madrid used 20 years of surveys from two groups of health professionals to draw their conclusion: death does not come any sooner for those who drink more coffee.

"I think the main conclusion is that, for those coffee drinkers, they can be quite sure that coffee doesn't increase their risk of death," said Esther Lopez-Garcia, the study's lead author.

So, time to break out the Folgers or head over to Starbucks, right?

Not so fast. People love drinking coffee -- the National Coffee Association estimates that the United States imported almost 6 million bags in the last three months of 2006 alone; so, coffee, like red wine or dark chocolate, is a popular choice for these kinds of studies.

But the results are not uniform. Some studies say there is no harm, others proclaim a benefit, while still others warn of dire consequences if you so much as look at that cup of joe in the morning.

Wake Up and Smell the Research

So, what are we to make of this latest news?

"It's one more study to add to the puzzle, but the message remains: Coffee in a healthful eating plan is OK, but it's not a magic food," said Connie Diekman, former president of the American Dietetic Association.

In other words, coffee isn't going to hurt you, but there's no need to start gulping it down if you weren't drinking it before. While the study is new, its findings aren't that different from what your doctor probably would have told you.

"This has been studied for decades, and putting all the studies together, there is no benefit nor harm," said Dr. Gordon A. Ewy, chief of cardiology at the University of Arizona College of Medicine, who was not involved with the study.

Even the researchers on this study say the findings should be taken with caution.

"Epidemiological studies have many limitations, and we need more studies in different populations with similar results in order to understand how diet can have an effect in our health," said Lopez-Garcia.

Those repeated, confirming studies are how health recommendations are made by licensed dieticians, said Joan Salge Blake, a spokesperson for the American Dietetic Association, and professor of nutrition at Boston University.

"You never take one study as the definitive study -- it's always based on a whole collection of studies," she said.

While it may not be as exciting when a food study confirms what we know, but a study with unprecedented results will need to be repeated before dieticians will make recommendations based on it.

"If it's brand new, say 'that's interesting,' don't say 'it's the definitive last word on it,'" said Blake. "All our recommendations are when the science is strong enough, enough of it is in, and it's all science-based. When enough science supports the recommendation, that's when the recommendation gets made."

All Diets Are Personal Diets

Blake adds that when a dietician works with a patient, they will look at medical history and other factors before deciding what recommendations to make for them.

Lopez-Garcia acknowledges this lack of a one-size-fits-all diet, saying that "people with hypertension, insomnia, and anxiety should ask their doctors before starting drinking coffee."

There may be little fault in this study's findings -- perhaps because they have been found in many other studies -- but even this study has its own potential problems.

"One cannot discount the possibility of a bias known as 'reverse causation,'" said Charles Poole, an epidemiologist at the University of North Carolina School of Public Health. "Sick people may be avoiding or cutting down on coffee. This would make coffee look protective."

The lesson is that each study, no matter how well-designed, will have its limitations.

"Epidemiology is attractive to the general public and the media because its findings are directly relevant to free living humans," said Dr. Charles Hennekens, a professor at Florida Atlantic University, who first looked at coffee's impact on health in the 1970s. "It is also true, however, that epidemiology is crude and inexact, as observations of free living humans can never take place under the controlled conditions in a laboratory."

Repeated findings over multiple studies are the key to making decisions about diets, because of the flaws any individual study will have.

"No one study is ever the definitive word on anything," said Blake.