Letters to the Editor
To the Editor:
Consumption of tea (especially green tea) is generally associated with a decreased risk of cancer although studies are not entirely consistent.1,2 We know of no studies that have examined the association between tea consumption and liver cancer.
We conducted an analysis based on 89,789 subjects 25–69 years of age who were enrolled in a cohort study in Haimen, China in 1992.3 The protocol was approved by the Institutional Review Board of the Fox Chase Cancer Center, the Medical Ethics Review Group of Haimen City, and the Ethics Review Committee of the Shanghai Medical University. The participants completed a questionnaire and provided a blood specimen at baseline. The vital status of study participants is determined annually. Tea drinkers were defined as those who drank tea at least 4 times a week. Liver cancer deaths were identified according to the International Classification of Disease 10th revision code C22. Cox proportional hazards model was used for multivariate analysis.
At baseline, 17% of men and 7% of women were regular tea drinkers. A total of 1803 deaths (men, 1536; women, 267) from liver cancer occurred as of 31 December 2006, with a total of 1,147,713 person-years of follow-up. The disease mortality was 200/100,000 for men and 70/100,000 for women. Both male and female tea drinkers had a lower mortality rate for liver cancer compared with people who did not regularly drink tea (Table 1). There was a strong protective effect among women (hazard ratio = 0.52), which was unchanged by adjustment for age, surface antigen of hepatitis B virus, occupation, history of hepatitis, family history of liver cancer, smoking, and alcohol drinking. The association was weaker in men, and was weakened further with adjustment.
Our data suggest that tea consumption may reduce the risk of liver cancer in women. Reasons for the sex disparity are not obvious. A recent study has suggested that an estrogen-mediated inhibition of serum interleukin-6 production by Kupffer cells reduces the risk of liver cancer in women.4 Tea may alter sex hormone levels associated with cancer risk.5 Although the information on type of tea was not collected, green tea is the dominant type of tea consumed in the study area. Further studies should examine the association of green tea and liver cancer.
Department of Epidemiology
School of Public Health
Shanghai, People's Republic of China
Haimen City Center for Disease Control and Prevention
Haimen City, People's Republic of China
Department of Epidemiology and Community Medicine
University of Ottawa
Ottawa, Ontario, Canada
1. Tsubono Y, Nishino Y, Komatsu S, et al. Green tea and the risk of gastric cancer in Japan. N Engl J Med.
2. Larsson SC, Wolk A. Tea consumption and ovarian cancer risk in a population-based cohort. Arch Intern Med
3. Evans AA, Chen G, Ross EA, et al. Eight-year follow-up of the 90,000-person Haimen City cohort: I. Hepatocellular carcinoma mortality, risk factors, and gender differences. Cancer Epidemiol Biomarkers Prev
4. Naugler WE, Sakurai T, Kim S, et al. Gender disparity in liver cancer due to sex differences in MyD88-dependent IL-6 production. Science
5. Nagata C, Kabuto M, Shimizu H. Association of coffee, green tea, and caffeine intakes with serum concentrations of estradiol and sex hormone-binding globulin in premenopausal Japanese women. Nutr Cancer