From 1980 through 1994, participants in the NHS gradually decreased the amount of caffeinated coffee they consumed and the number of NHS participants who did not drink coffee also decreased. In 1980, 22.5% of the women did not drink coffee, and 25.0% drank four or more cups of caffeinated coffee per day. In 1994, 13.2% of the women did not drink coffee, and 14.2% drank four or more cups per day. A similar, but weaker, trend toward decreased coffee consumption was observed among participants in the HPFS. In 1986, 29.9% of the men did not drink caffeinated coffee, and 10.8% drank four or more cups per day. In 1994, 22.3% of the men drank no coffee and 8.8% drank four or more cups daily. Similar patterns emerged for tea consumption in the two cohorts. Accordingly, mean caffeine intake decreased from 391 mg/day (standard deviation [SD] = 270 mg/day) in 1980 to 242 mg/day (SD = 207 mg/day) in 1994 among all women and from 227 mg/day (SD = 227 mg/day) in 1986 to 221 mg/day (SD = 221 mg/day) in 1994 among all men.
The number of participants who reported drinking decaffeinated coffee increased over time. Among women, 49.3% drank decaffeinated coffee with any regularity in 1984 and 71.5% did so in 1994. Among men, 48.8% drank decaffeinated coffee with any regularity in 1986, whereas 62.5% did so in 1994.
Coffee consumption varied greatly among the participants in each cohort. Although in both cohorts the most frequent category of caffeinated coffee consumption selected was two to three cups per day, considerable numbers of participants reported that they either consumed no coffee or more than five cups per day (). Higher consumption of caffeinated coffee was associated with a lower mean body mass index among women and with a higher mean body mass index among men. In both cohorts, higher caffeinated coffee consumption was also associated with a lower frequency of sigmoidoscopy, a lower use of vitamin supplements, and higher frequencies of smoking, alcohol consumption, aspirin use, and red meat consumption. Higher consumption of decaffeinated coffee was associated with higher frequencies of sigmoidoscopy, vitamin supplement use, and smoking in both cohorts and with a higher frequency of aspirin use among men. In both cohorts, higher tea consumption was associated with lower alcohol consumption. Patterns for caffeine intake were similar to those for caffeinated coffee consumption ().
Age-standardized distribution of covariates during follow-up, by frequency of caffeinated and decaffeinated coffee and tea consumption and caffeine intake*
During 1 479 804 person-years of follow-up among women, we documented 731 cases of colon cancer and 155 cases of rectal cancer; during 511 801 person-years of follow-up among men, we documented 446 cases of colon cancer and 106 cases of rectal cancer.
Total coffee consumption, which included caffeinated and decaffeinated coffee consumption, was not associated with the incidence of colorectal, colon, or rectal cancer. The covariate-adjusted hazard ratios for colorectal cancer for each additional cup of any coffee consumed were 0.99 (95% confidence interval [CI] = 0.95 to 1.04) among women and 0.98 (95% CI = 0.92 to 1.03) among men.
Results of our analysis of the association between caffeinated coffee consumption and incidence of colorectal cancer are presented in . Because the hazard ratios adjusted for age only did not differ appreciably from the hazard ratios adjusted for all covariates, we present only the latter in . We found no significant association between consumption of caffeinated coffee and the incidence of colorectal cancer (). Participants who reported never drinking caffeinated coffee had a crude incidence rate of colorectal cancer of 71 cases per 100 000 person-years of follow-up while those who reported drinking more than five cups of caffeinated coffee per day had a crude incidence rate of colorectal cancer of 52 cases per 100 000 person-years of follow-up. Among women and men combined, the pooled hazard ratio for colorectal cancer for one additional cup of caffeinated coffee per day was 1.01 (95% CI = 0.97 to 1.04) when we adjusted for age only and 0.99 (95% CI = 0.96 to 1.03) when we adjusted for age, family history of colorectal cancer, history of sigmoidoscopy, height, body mass index, pack-years of smoking, physical activity, aspirin use, vitamin supplement intake, total caloric intake, alcohol consumption, red meat consumption, and, among women, menopausal status and postmenopausal hormone use. Compared with no consumption, consumption of four or more cups of coffee per day was associated with a slight although not statistically significant increase in rectal cancer (pooled HR = 1.55, 95% CI = 0.97 to 2.45). No statistically significant trend of higher rectal cancer incidence emerged with increasing coffee consumption (Ptrend = .31). When we only used coffee consumption reported in 1980 for women and 1986 for men and did not update consumption during follow-up, the results did not differ from the results presented for cumulatively updated coffee consumption (data not shown).
Cumulative updated caffeinated coffee consumption and covariate-adjusted hazard ratio of colorectal, colon, and rectal cancers*
Women and men who drank decaffeinated coffee had a lower incidence of colorectal cancer, particularly rectal cancer, than women and men who never drank decaffeinated coffee (). Participants who reported never drinking decaffeinated coffee had a crude incidence rate of rectal cancer of 19 cases per 100 000 person-years of follow-up while those who reported drinking two or more cups of decaffeinated coffee per day had a crude incidence rate of rectal cancer of 12 cases per 100 000 person-years of follow-up. Participants who reported any regular consumption of decaffeinated coffee had approximately half the risk of rectal cancer than those who did not drink decaffeinated coffee. Women and men who drank two or more cups of decaffeinated coffee per day had a 52% (95% CI = 19% to 71%) lower risk of rectal cancer than women and men who did not drink decaffeinated coffee after adjusting for all covariates used in this analyses as well as for caffeinated coffee consumption; however, the relation between consumption frequency and rectal cancer risk was not linear. Colon cancer incidence was lowest among participants who drank a daily average of half a cup of decaffeinated coffee. When we performed separate analyses for colon cancers at proximal and distal sites, we found that the reduction in colon cancer risk associated with consumption of decaffeinated coffee was restricted to men and women who had been diagnosed with proximal site colon cancers but that this risk reduction was not statistically significant (data not shown). When we chose participants who reported that they never drank caffeinated or decaffeinated coffee as the referent group, the results did not differ appreciably (data not shown). When we used information about decaffeinated coffee consumption from the first questionnaires only (the 1984 questionnaire for women and the1986 questionnaire for men), the results were similar to those obtained using updated information about decaffeinated coffee consumption (data not shown).
Cumulative updated decaffeinated coffee consumption and covariate-adjusted hazard ratio of colorectal, colon, and rectal cancer*
Tea consumption was not associated with the incidence of either colon or rectal cancer (). Similarly, there was no significant association between total caffeine intake and the incidence of either colon or rectal cancer ().
Cumulative updated tea consumption and covariate-adjusted hazard ratio of colorectal, colon, and rectal cancer*
Cumulative updated caffeine consumption and covariate-adjusted hazard ratio of colorectal, colon, and rectal cancer*
When we restricted our analyses to women and men who did not currently smoke cigarettes, the results were not materially different from the results observed among the entire study population (). Similarly, results of analyses that were restricted to participants who did not smoke cigarettes and did not drink alcoholic beverages were not materially different from those obtained for the entire study population ().
Cumulative updated consumption of caffeinated coffee, decaffeinated coffee, tea, and caffeine and covariate-adjusted hazard ratio of colorectal cancer among nonsmokers and among women and men who do not smoke and do not drink alcohol*