Coffee consumption may reduce the risk for endometrial cancer, according to a study published in The Journal of Obstetrics and Gynaecology Research.
Yu Gao, of the departments of obstetrics and gynecology at Liangxiang Hospital of Beijing Fangshan District and at Peking Union Medical College Hospital, both in Beijing, and colleagues reviewed 24 observational studies that included 9,833 incident cases of endometrial cancer and 699,234 patients.
There were 12 case-control studies (4,022 cases; 19,839 subjects) and 12 prospective cohort studies (5,811 cases; 679,395 subjects) investigating the association between coffee consumption and the risk for endometrial cancer.
The pooled RR of endometrial cancer was 0.71 (95% CI, 0.65-0.77) for the highest vs. the lowest categories of coffee intake. The case-control studies had a pooled RR of 0.68 (95% CI, 0.56-0.83), and the cohort studies had a pooled RR of 0.7 (95% CI, 0.63-0.77).
Europe and the United States/Canada had similar pooled RRs of endometrial cancer of 0.74 (95% CI, 0.62-0.88) and 0.71 (95% CI, 0.64-0.79), respectively, but Japan had a pooled RR of 0.4 (95% CI, 0.28-0.57). The researchers attributed these differences to varying genetic backgrounds, lifestyles, dietary patterns and endometrial cancer incidences.
In the six studies on different types of coffee, caffeinated coffee had a pooled RR of 0.66 (95% CI, 0.52-0.83), and decaffeinated coffee had a pooled RR of 0.86 (95% CI, 0.71-1.04). The researchers noted that caffeine intake may directly affect sex hormone binding globulin levels, inhibiting the risk for endometrial cancer.
In two studies, the researchers found a pooled RR for filtered coffee of 0.77 (95% CI, 0.38-1.53) and 0.56 (95% CI, 0.3-1.04) for boiled coffee, leading them to suggest there was no significant association between cancer risk and how the coffee was made.
Eight studies that looked at coffee, BMI and endometrial cancer risk found a pooled RR of 0.65 (95% CI, 0.54-0.79) for higher BMI and 0.88 (95% CI, 0.75-1.03) for lower BMI. The bioactive components in coffee benefit metabolism, the researchers said, and these benefits are more obvious in women with a higher BMI.
In six studies, there was a pooled RR for endometrial cancer of 0.56 (95% CI, 0.45-0.7) among coffee drinkers who had smoked at some point and 0.68 (95% CI, 0.56-0.84) among those who had never smoked.
The researchers noted potential synergy between the bioactive ingredients of both coffee and cigarette smoke in endometrial carcinogenesis, as the same family of cytochrome P450 enzymes metabolizes caffeine, nicotine and estrogen molecules.
Finally, in three studies, the pooled RR was 0.88 (95% CI, 0.79-0.98) for coffee drinkers who never used hormone replacement therapy and 0.97 (95% CI, 0.92-1.02) for coffee drinkers who had.