After 13.3 years of follow-up, there were 280 epithelial ovarian carcinomas, 47.1% of which were serous carcinomas, 10.0% mucinous carcinomas, 9.3% endometrioid carcinomas and 4.3% clear cell carcinomas. Tea was drunk by >89% of the subjects, coffee by >96% and only 0.2% drank neither. Mean daily tea consumption (s.d.) was 3.1 (2.1) cups for subcohort members and 2.9 (1.8) cups for cases. Older women, never smokers, more highly educated respondents and women with a normal body mass index (BMI) drank more tea. Mean daily coffee consumption (s.d.) was 4.0 (2.0) cups for subcohort members and 4.1 (2.0) cups for cases. A lower age, current smoking, a lower level of education and a higher BMI were associated with higher coffee consumption.
shows RRs for ovarian cancer for tea and coffee consumption. Tea consumption was inversely associated with ovarian cancer risk, although not statistically significant and coffee consumption showed no association. The proportional hazards assumption was not violated and there was no effect modification. The category 1–<3 cups per day was chosen as a reference because there were too few subjects in the lowest category. We excluded subjects with <2 years of follow-up to check for protopathic bias, analysed stable coffee drinkers separately and corrected for acrylamide in coffee, but none of these analyses affected the results. Subtype analyses showed that tea was inversely associated with serous tumours, whereas it was related to increased risk of mucinous and endometrioid tumours, giving some indication for heterogeneity.
Rate ratios of ovarian cancer according to coffee and tea consumptiona
In the meta-analysis (), tea was found to be inversely associated with ovarian cancer when study results were pooled. The association was strongest, and statistically significant, in cohort studies. Coffee consumption was related to increased ovarian cancer risk when study results were pooled. A stronger, borderline significant association was seen in cohort studies.
Figure 1 Meta-analysis of case-control and cohort studies investigating tea and coffee consumption (highest vs lowest) in relation to ovarian cancer risk. Note: In this meta-analysis, we used the lowest category as a reference in all studies, for reasons of comparability. (more ...)