Daily consumption of caffeinated coffee may prevent a recurrence of colon cancer in people treated for the disease with the strongest benefits for those drinking at least four cups, according to new scientific research.
The new findings come with caveats -- and for some doctors, raise a long list of questions.
Pending further research, scientists at the Dana-Farber Cancer Institute in Boston, who conducted the study, said people should not begin drinking coffee if they aren't already java drinkers. Those who drink it should not increase their number of daily cups, the scientists said.
The study is the first ever to examine whether coffee plays a role in preventing colon cancer recurrence and lowers mortality from the disease among U.S. residents -- who consume the most coffee globally.
Dr. Jules Garbus, co-chief of colon and rectal surgery at Winthrop-University Hospital in Mineola, said the research cannot be easily dismissed because it raises questions about how coffee affects metabolism.
"Diet and lifestyle affect people's cancer risk," Garbus said. He also noted that Dana-Farber's reputation adds credence to the findings. The study's lead investigator, Dr. Charles Fuchs, said it was unclear why coffee didn't prevent the patients' cancers in the first place.
"We only identified subjects following the diagnosis of colon cancer so we don't have their coffee consumption prior to diagnosis," he said in an email.
Fuchs, director of the Gastrointestinal Cancer Center at Dana-Farber, said people with metabolic disorders have a higher colon cancer risk.
For example, high levels of insulin are associated with elevated risks of the cancer because the hormone can promote the growth of cancer cells. Obesity also is associated with higher colon cancer risk and higher levels of insulin in the blood.
Caffeine helps lower insulin levels and is associated with decreased risk of type 2 diabetes, Fuchs wrote in the study.
Nearly 1,000 patients were involved in the research. All had been treated with surgery and chemotherapy. Those who had the best five-year survival rates drank at least four cups of caffeinated coffee daily, consuming about 460 milligrams of caffeine. There was no correlation between a survival benefit and herbal tea consumption, the study found.
Results of the analysis were reported in Monday's Journal of Clinical Oncology. Patients who consumed four daily cups were 42 percent less likely to experience a rebound of their cancer and were 33 percent less likely to die from the disease.
Dr. Robert Amajoyi, a colorectal cancer surgeon at South Nassau Communities Hospital in Oceanside, said while the research sheds new light on a role that coffee might play, he is not yet convinced of a cause-and-effect.
"Coffee has potential anti-mutagenic properties," he said Monday, referring to antioxidants that may help prevent mutations. But it is impossible to say how java consumption affects cancer risk without stronger research, he said.
"That's why I say more studies are required," Amajoyi said, adding that rather than the questionnaire used by the Boston team, he would prefer to see a randomized double-blind placebo-controlled study, the gold standard of scientific research.
Dr. Peter Bach, a physician and epidemiologist who directs the Center for Health Policy and Outcomes at Memorial Sloan-Kettering Cancer Center in Manhattan, also said more powerful data are required.
"Coffee drinking and lower risk may be related to an unseen third factor. I'm not saying that is the case, but we would only know if this were a true risk-reducing intervention with a randomized trial," Bach said. The National Coffee Association, which was not involved in the research, estimates about 83 percent of U.S. adults drink coffee. Each person averages about three cups a day for a total of 587 million daily cups, according to the association's 2013 survey.
Cancers of the colon and rectum are together the third most commonly diagnosed malignancies in the United States in both men and women, according to the American Cancer Society. The organization estimates 132,700 new cases will be diagnosed this year.
Although the death rate has been declining over the past 20 years, survival has been highest for people with stage 1 disease, which is 92 percent at five years, additional statistics from the cancer society show. At stage 3-A, five-year survival is 89 percent; stage 3-B 69 percent, and 53 percent at stage 3-C. For people diagnosed with stage 4 colon cancer, the five-year survival rate is 11 percent.