Two new studies in the February 16 issue of the Journal of the National Cancer Institute examine the effects of coffee consumption on the incidence of liver and colorectal cancers. One study found that drinking coffee daily is associated with a decreased risk of liver cancer, while the other found no association between drinking coffee or tea and the risk of colorectal cancer.
Coffee consumption is common throughout the world, but the benefits or risks of the drink are not completely known. Evidence suggests that coffee consumption may be associated with a decreased risk of hepatocellular carcinoma (HCC), a type of liver cancer. The evidence for any association with colorectal cancer is less clear.
In the first study, Manami Inoue, M.D., Ph.D., of the National Cancer Center in Tokyo, and colleagues conducted a population-based cohort study of middle-aged and elderly Japanese subjects from the Japan Public Health Center-Based Prospective Study.
People who drank coffee on a daily or almost daily basis had about half the risk of HCC compared with those who never drank coffee. In the population studied, the rate of liver cancer among those who never drank coffee was 547.2 cases per 100,000 people over 10 years, but among daily coffee drinkers the rate was 214.6 cases per 100,000 people. In addition, the risk of HCC decreased with an increase in the amount of coffee consumed each day.
However, the authors caution that because decaffeinated coffee is rarely consumed in Japan, and therefore no distinction was made between caffeinated and decaffeinated coffee, it cannot be determined if caffeine is responsible for the decreased risk of HCC. In addition, the results need to be confirmed among people who are infected with hepatitis, the authors say.
"The present cohort analysis confirmed a statistically significant inverse association between habitual coffee drinking and HCC," Inoue and colleagues write. "Further studies are warranted to assess whether the present results can be generalizable or are representative of other populations."
In the second study, Karin B. Michels, Sc.D., of Brigham and Women's Hospital in Boston, and colleagues used data from two large prospective studies, the Nurses' Health Study (women) and the Health Professionals' Follow-up Study (men), to explore the association between coffee, tea, and caffeine consumption and the incidence of colorectal cancer during almost 2 million person-years of follow-up.
They found no association between consumption of caffeinated coffee or tea and the incidence of colon or rectal cancer in either group. Participants who regularly drank two or more cups per day of decaffeinated coffee, however, had about half the incidence of rectal cancer compared with those who never drank decaffeinated coffee. In the population studied, the rate of rectal cancer was 12 cases per 100,000 person-years of follow-up among those who consumed two or more cups of decaffeinated coffee per day. Among those who never drank decaffeinated coffee, the rate was 19 cases of rectal cancer per 100,000 person-years of follow-up. The authors caution that this observed association may be due to differences in lifestyle because drinkers of decaffeinated coffee might be more health conscious in their behaviors than those who consume caffeinated coffee.
"[W]e found that regular consumption of caffeinated coffee or tea or total caffeine intake was not associated with a reduced incidence of colon or rectal cancers," Michels and colleagues write. "Although consumption of decaffeinated coffee was inversely associated with the incidence of rectal cancer, this association needs to be confirmed in other studies."