Coffee particularly regular brewed coffee
Coffee, particularly regular brewed coffee, and tea are among commonly consumed beverages in Canada . Despite the existence of biologically plausible evidence suggesting that these beverages, as well as caffeine, may influence a woman’s risk of cancer, very few studies have been conducted to assess their role in the development of cancers among Canadian women [13,37]. Thus, in this study we examined the association between coffee, tea and caffeine intake and risk of cancers of the breast, endometrium, and ovary among women in the Canadian Study of Diet, Lifestyle, and Health (CSDLH).
Materials and methods
Results Baseline characteristics are summarized in Table 1. Median follow-up time for the study Heparin was 12.2 years (interquartile range: 9.2–15.7 years). Table 2 shows that there were no associations between coffee, tea, and caffeine intake and risk of breast cancer overall. Table 3, Table 4 show the HRs (95% CI) for the associations of coffee, tea and caffeine intake with risk of breast cancer by menopausal and HRT status and BMI strata. There was some suggestion of an increased risk of breast cancer with increasing levels of caffeinated coffee among premenopausal women (p for trend: 0.08). There was also a tendency towards an increased risk of breast cancer with increasing levels of total coffee, caffeinated coffee and caffeine among normal weight women (p for trend: 0.05, 0.07 and 0.05 respectively). However, the associations of coffee and caffeine intake with risk of breast cancer did not vary by HRT ever (users vs. never) (Table 3). The associations between coffee, tea and caffeine intake and risk of endometrial cancer are shown in Table 5. Per cup increase in total coffee and caffeinated coffee intake was associated with 12% decreased risk of endometrial cancer, respectively (HR: 0.88; 95% CI: 0.79-0.95, and 0.88; 0.80-0.96, respectively). Per 100 mg increase in caffeine was also associated with 7% reductions in risk of endometrial cancer (HR: 0.93; 95% CI: 0.87-0.99). There was also a trend towards a reduced risk of this cancer with increasing levels of total and caffeinated coffee. Decaffeinated coffee and tea intake were not associated with risk. Table 6 shows the associations of coffee, tea and caffeine intake with risk of ovarian cancer. None of the beverages or caffeine was associated with risk.
Discussion Our findings of no association between total coffee intake and risk of breast cancer overall are in keeping with those of previous studies [, , , , , ,29,46]. However, findings from a meta-analysis and one recent prospective study indicated a weak inverse association between total coffee intake and overall risk of breast cancer [20,21] while in an earlier case-control study, a positive association was observed . It is well-established that a woman’s menopausal status, HRT -status, and level of adiposity affect her risk of breast cancer [48,49]. However, very few studies have assessed the modifying effect of these risk factors on the association between coffee, tea and caffeine intake and risk. While we did not observe an association between these dietary factors and overall risk of breast cancer, there was some suggestion that caffeinated coffee may be positively associated with risk of breast cancer among premenopausal women. This finding is in contrast to four previous prospective studies which found no association between caffeinated coffee intake and risk of breast cancer among premenopausal women [14,16,20,50] and one case-control study, in which an inverse association was reported . Some studies also yielded an inverse association between coffee and caffeine intake with risk of breast cancer among postmenopausal women [16,20,52], but similar to our study, null findings have been documented in others [14,50,51]. In line with existing studies, our study did not show that the association between tea consumption and risk of breast cancer according to menopausal status [14,16,20,50].