TUESDAY, Feb. 15, 2005 (HealthDay News) -- Coffee drinkers may have reason to smile: Daily coffee consumption seems to reduce the risk of liver cancer, a new study finds.
And drinking decaffeinated coffee seems to cut colorectal cancer risk, another study claims.
Both papers appear in the Feb. 16 issue of the Journal of the National Cancer Institute.
"We were surprised. We didn't expect the decaf findings," said Karin B. Michels, an associate professor of epidemiology at Harvard Medical School, and lead author of the study that looked at caffeine consumption and colorectal cancer risk.
The researchers were trying to confirm conflicting results from earlier studies, some finding that coffee reduced colorectal cancer risk and others revealing no effect. They evaluated data from two large studies, the Nurses' Health Study and the Health Professionals' Follow-up Study, together including more than 173,000 men and women. The goal was to look at the association between coffee, tea and caffeine consumption and the incidence of colorectal cancer.
They found no association between consumption of caffeinated coffee or tea and the incidence of colon or rectal cancer in either group. But they found that those who regularly drank two or more cups of decaffeinated coffee a day had about half the rate of rectal cancer as those who never drank decaf coffee.
It had been theorized that increased bowel motility [movements] from coffee consumption was "one of the most important mechanisms" in the reduction of cancer risk, said Michels. "We set out to confirm that, but we did not find an association between caffeine consumption and lower cancer risk."
It could be, she speculated, that decaffeinated coffee has an effect on bowel motility, but something in caffeine cancels out that effect.
The finding needs to be confirmed in other studies, Michels said, before any recommendation about coffee drinking can be made.
In the second study, Dr. Manami Inoue of the National Cancer Center in Tokyo and colleagues followed more than 90,000 middle-aged and elderly Japanese men and women for 10 years. They found that those who drank coffee daily or almost daily had half the risk of liver cancer, compared to those who did not drink coffee. They didn't differentiate between caffeinated or decaffeinated coffee, but noted that decaf coffee is rarely consumed in Japan.
The rate of liver cancer among those who never drank coffee was 547.2 cases per 100,000 people over a decade, but the rate among daily coffee drinkers was 214.6 cases per 100,000 over the same period.
"In our study, liver cancer risk significantly decreased with the amount of coffee consumed (compared with nondrinkers, 48 percent decrease with 1-2 cups per day; 52 percent decrease for 3-4 cups per day; 76 percent decrease for 5 cups per day)," Inoue said. "Our results are consistent with, but more pronounced than, those of previous case-control studies."
About 17,550 new cases of primary liver and bile duct cancers are expected to be diagnosed this year in the United States, according to the American Cancer Society. About 104,950 new cases of colon cancer and 40,340 of rectal cancer are expected to be diagnosed this year as well.
Dr. Michael J. Thun, head of epidemiological research for the American Cancer Society, said the two new studies are interesting, but the results shouldn't prompt any recommendations or changes in coffee-consumption habits.
"There isn't anything in these studies that would persuade people to give up or take up coffee drinking," Thun said, adding, "The liver finding is interesting, but needs to be replicated."
The finding that decaffeinated, but not regular, coffee reduced colorectal cancer risk is surprising to Thun, as it was to the study authors. "But it is important not to overinterpret," Thun said. Again, more research is needed to be sure the finding isn't a fluke, he added.
While the associations both bear more study, Thun said, "it's much too soon to go changing your diet."
More information
To learn more about cancers, visit the American Cancer Society.
