Coffee, green tea, and caffeine consumption and subsequent risk of bladder cancer in relation to smoking status: a prospective study in Japan

摘要

The incidence of bladder cancer is increasing slightly worldwide, particularly in industrial countries, including Japan.~(1-2)Many epidemiological studies have suggested that bladder cancer is influenced by environmental factors, such as smoking, exposure to industrial chemicals, and several lifestyle factors.~(3)While the International Agency for Research on Cancer (IARC) reported that coffee is a possible carcinogenic agent (group 2B) in bladder cancer, it could not exclude the possibility that this was due to bias or confounding.~(4) In a recent meta-analysis, Zeegers et al. demonstrated a small elevated risk (20%) of bladder cancer for current coffee drinkers,~(5) and a pooled analysis of 10 case-control studies in European countries found that heavy coffee consumption showed a positive association with bladder cancer among non-smokers.~(6)However, most of these previous studies were conducted in Western countries; and of the five conducted in Asian populations, results have been inconsistent: a prospective study in Japanese-Americans reported that coffee consumption increased the risk of bladder cancer albeit without a dose-response,~(7) two case-control~(8-9) and a prospective study~(10) among Japanese people found that the relative risk of coffee drinking was insignificant; while a case-control study in Japanese-American women showed an inverse association with coffee consumption~(11) These findings indicate that the relationship between coffee consumption and bladder cancer in Asian populations is largely unknown#