Coffee consumption and bladder cancer are linked, analysis showsBMJ 2015; 350 doi: https://doi.org/10.1136/bmj.h1477 (Published 18 March 2015) Cite this as: BMJ 2015;350:h1477
A long suspected link between coffee consumption and the development of bladder cancer has been confirmed by a new meta-analysis of 34 case-control and six cohort studies. The link was found to be stronger among males and non-smoking coffee drinkers.
Bladder cancer is a major health problem, being the most common type of cancer of the urinary tract and the ninth most common cancer among men, with nearly 330 000 new cases and 130 000 deaths reported worldwide every year.
Since the 1970s coffee consumption has been considered a risk factor for developing bladder cancer, and various potentially harmful components such as caffeine, polycyclic aromatic hydrocarbons, and nitrosamines have been cited as possible causative agents. However, previous studies have produced mixed results.
The new study, published on 12 March in the journal Scientific Reports,1 was the first to pool together over 30 years of research and more than 250 000 participants from different studies, including case-control and cohort studies.
It found a statistically significant association between coffee intake and the risk of bladder cancer, with an overall odds ratio of 1.33 (95% confidence interval 1.19 to 1.48). Furthermore, the summary odds ratio of bladder cancer with an increase of one cup of coffee a day was 1.05 (1.03 to 1.06) in case-control studies and 1.03 (0.99 to 1.06) in cohort studies—representing an increased risk of bladder cancer of 5% among the case-control group and 3% among the cohort group.
A surprising result was the reduced risk of developing bladder cancer seen among smokers (1.24 (0.91 to 1.70)) compared with non-smokers (1.72 (1.25 to 2.35)), which the authors attributed to coffee induced mechanisms affecting the onset of bladder cancer.
“There are interactions on the carcinogenic effect among coffee chemicals and other environmental agents, including polycyclic aromatic hydrocarbons in smoke,” said Qing Lu, a medical researcher from Huazhong University of Science and Technology in China and lead author of the paper. Results showed that the carcinogenic effect of coffee consumption on bladder cancer was reduced in the presence of smoke compounds, he added.
One idea behind this outcome is that caffeine, which may lead to the activation of carcinogenic compounds, is more quickly metabolised in smokers. Lu said, “Under this circumstance, time for exposure to caffeine will be shorter, which will reduce the carcinogenic effects of caffeine. Thus, the adverse effects of coffee and caffeine may be more clearly expressed among never or former smokers.
“In the next stage, animal experiments will be conducted to explore the underlying mechanisms.”
Cite this as: BMJ 2015;350:h1477