Coffee and tea lovers may have a decreased likelihood of developing the most common form of malignant brain tumor in adults, a new study suggests.
The findings, from a study of more than 500,000 European adults, add to evidence from a recent U.S. study linking higher coffee and tea intake to a lower risk of gliomas, a group of brain tumors that makes up about 80 percent of malignant brain cancers in adults.
It does not, however, prove that the beverages themselves confer the protection.
"This is all very preliminary," said lead researcher Dominique Michaud, of Brown University in Providence, Rhode Island, and Imperial College London. "This study shouldn't be the reason that anyone changes their coffee or tea intake."
And even if coffee and tea have some direct effect on glioma risk, the impact would be small. Brain tumors in general are uncommon; in Europe, for instance, annual rates are estimated at between four and six cases per 100,000 women, and six to eight cases for every 100,000 men.
Overall, the odds that a person will develop a malignant (cancerous) brain tumor in his or her lifetime are less than 1 percent.
Still, Michaud said, if higher coffee and tea intake is somehow protective against glioma, that could give researchers insight into the causes of the tumors. "Right now, we don't know much about what causes brain cancer," she noted in an interview.
The findings, published in the American Journal of Clinical Nutrition, come from an ongoing study in 10 European countries investigating potential risk factors for cancer. At the outset, 521,488 men and women between the ages of 25 and 70 completed detailed questionnaires on their medical history, diet, exercise habits, smoking and other lifestyle factors.
For their analysis, Michaud's team focused on more than 410,000 participants who were cancer-free at the outset and had complete dietary information. Over an average of 8.5 years of follow-up, 343 of these men and women were diagnosed with glioma; another 245 were diagnosed with another, usually benign type of brain tumor called meningioma.
When the researchers divided the study participants into four to five groups based on their coffee and tea intake at the outset, they found no evidence of a "dose-response" relationship — that is, a decreasing glioma risk as coffee and tea consumption climbed.
The findings were different, however, when the researchers looked at two groups: those who averaged at least 3.5 ounces of coffee or tea per day, and those who drank less or none at all.
The heavier coffee/tea consumers were one-third less likely to be diagnosed with glioma, with factors such as age and smoking history taken into account. There was no connection seen with meningioma risk.
According to Michaud, it's not clear why there was no evidence of a dose-response association between coffee and tea intake and the risk of glioma — which is generally considered a stronger sign of a possible cause-and-effect relationship. But it may be related to difficulties in precisely measuring study participants' coffee and tea intake, which was dependent on self-reports.
It is biologically plausible that coffee and/or tea could affect glioma risk, Michaud said.
A recent lab study, for example, found that caffeine appeared to slow the growth of a type of glioma called glioblastoma. In addition, both coffee and tea contain antioxidants, which help protect body cells from damage that can lead to cancer and other diseases.
However, it's also possible that coffee and tea enthusiasts have other characteristics that might affect their likelihood of glioma development. Just what those characteristics might be is unknown, as the causes of most brain tumors are unknown.
Researchers know of some risk factors. People who undergo radiation therapy — most commonly radiation of the head to treat other cancers — have a heightened risk of a future brain tumor. And genetic predisposition appears to play a role in a small percentage of brain tumors.
But the evidence on dietary or environmental factors, like on-the-job chemical exposures, has been inconclusive.
Michaud said that more research is needed both to confirm that there is an association between coffee and tea intake and glioma risk, and to understand the underlying reasons.