From the aMetabolic Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD; and bBiostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD.
Epidemiology. 2017 Sep;28(5):685-693. doi: 10.1097/EDE.0000000000000676.
In 1991, coffee was classified as a group 2B carcinogen, possibly carcinogenic to humans, based on limited epidemiologic evidence of a positive association with bladder cancer. In 2016, the International Agency for Research on Cancer downgraded this classification due to lack of evidence from prospective studies particularly for never smokers.
Baseline coffee drinking was assessed with a food frequency questionnaire in the NIH-AARP prospective cohort study. Among 469,047 US adults, who were cancer free at baseline, 6,012 bladder cancer cases (5,088 men and 924 women) were identified during >6.3 million person-years of follow-up. Multivariable-adjusted Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI), with non-coffee drinkers as the reference group.
Coffee drinking was positively associated with bladder cancer in models adjusted for age and sex (HR for ≥4 cups/d relative to coffee nondrinkers = 1.91, 95% CI = 1.70, 2.14; P trend < 0.0001). However, the association was substantially attenuated after adjustment for cigarette smoking and other potential confounders (HR for ≥4 cups/d relative to coffee nondrinkers = 1.18, 95% CI = 1.05, 1.33; P trend = 0.0007). Associations were further attenuated after additional adjustment for lifetime smoking patterns among the majority of the cohort with this available data (P trend = 0.16). There was no evidence of an association among never smokers (P trend = 0.84).
Positive associations between coffee drinking and bladder cancer among ever smokers but not never smokers suggest that residual confounding from imperfect measurement of smoking or unmeasured risk factors may be an explanation for our positive findings.
1991 年，咖啡被归类为 2B 组致癌物，可能对人类致癌，这一结论基于有限的流行病学证据表明咖啡与膀胱癌之间存在正相关关系。2016 年，由于缺乏来自前瞻性研究的证据，特别是对于从不吸烟的人，国际癌症研究机构降低了这一分类。
在美国 NIH-AARP 前瞻性队列研究中，使用食物频率问卷评估基线时的咖啡饮用情况。在 469047 名无癌症的美国成年人中，在 >630 万人年的随访期间，共发现 6012 例膀胱癌病例（5088 名男性和 924 名女性）。使用多变量调整的 Cox 比例风险模型来估计风险比（HR）和 95%置信区间（CI），以不喝咖啡者为参照组。
在调整了年龄和性别因素的模型中，咖啡饮用与膀胱癌呈正相关（与不喝咖啡者相比，每天饮用≥4 杯咖啡者的 HR = 1.91，95%CI = 1.70，2.14；P 趋势<0.0001）。然而，在调整了吸烟和其他潜在混杂因素后，这种相关性显著减弱（与不喝咖啡者相比，每天饮用≥4 杯咖啡者的 HR = 1.18，95%CI = 1.05，1.33；P 趋势=0.0007）。在对具有可用数据的大多数队列中进行终生吸烟模式的进一步调整后，这种相关性进一步减弱（P 趋势=0.16）。从不吸烟者中没有发现相关性（P 趋势=0.84）。
在曾吸烟者中，咖啡饮用与膀胱癌之间存在正相关关系，但在从不吸烟者中则没有，这表明吸烟或未测量的危险因素的不完全测量可能是我们阳性结果的解释。
