Coffee and bladder cancer
Studies provided sufficient evidence for the Institute of Cancer Research (IARC) to conclude that there is inadequate evidence of an association between coffee intake and bladder cancer, highlighting that smoking may have confounded results in some of the early studies1.
Additionally, the World Cancer Research Fund (WCRF) 2018 Bladder Cancer Report lists coffee under ‘limited evidence - no conclusion’57. Some work has also suggested variable results in an Asian population and in male coffee drinkers, so further research is clearly required.
- A number of meta-analyses have reviewed the associations between coffee consumption and bladder cancer risk, presenting variable results58-63. Based on current research it is difficult to draw firm conclusions about associations between coffee consumption and bladder cancer risk. For instance, a 2015 meta-analysis of observational studies, including 34 case control studies and 6 cohort studies, suggested an increased risk of bladder cancer among coffee drinkers61
- A 2017 study following 73,346 Japanese individuals where 274 cases of bladder cancer were identified, concluded that the data indicates a significant inverse association between coffee consumption and bladder cancer62
- A 2020 analysis of 12 cohort studies in Japan concluded that an increased risk of bladder cancer was seen among coffee drinkers in male smokers but not those who had never smoked, or in females. The authors suggested that the results were unlikely to be causal and possibly caused by residual confounding of smoking63
Research investigating a dose response relationship between coffee intake and bladder cancer is also limited.
- A 2014 meta-analysis found no association between coffee consumption and bladder cancer, but since the authors reported insignificant associations in analysis of intakes (highest vs. none/lowest) and in dose response analyses, further research is again required60
As noted above, a number of confounding factors have been reported, including smoking, maleness and Asian origin.
- Two meta-analyses suggest that compared with smokers, non-smokers appear to have a slightly increased risk of bladder cancer60,61
- A 2017 Japanese study concluded that an inverse association between coffee consumption and bladder cancer was observed even when stratified for smoking status62
- Further data suggests that coffee consumption is associated with a decreased risk of bladder cancer in Asian people60
- Some research also suggests an increased risk of bladder cancer in male coffee drinkers61
Clearly, further work is required to understand these associations in more detail.
Coffee and kidney cancer
Research consistently suggests there is no conclusive link between coffee consumption and kidney cancer64. During the last three decades, the incidence of kidney cancer has constantly increased, leading to the search for possible links with diet. The WCRF 2018 Kidney Cancer Report lists coffee under ‘Limited Evidence – No Conclusion’65 and the 2016 IARC Report concluded that there is inadequate evidence to suggest any association between coffee consumption and kidney cancer1.
- A 2017 meta-analysis of 22 observational studies (16 case-control and 6 cohort studies) concluded that there was no significant association between coffee consumption and renal cell carcinoma64. The authors advised that a potential role in reducing the risk of renal cell carcinoma, particularly in men, requires further investigations
Coffee and prostate cancer
Research suggests that coffee consumption is not associated with an increased risk of prostate cancer5,66-72, with a number of studies suggesting a reduced risk of the disease. The WCRF 2018 Prostate Cancer Report lists coffee under ‘limited evidence - no conclusion’73. Additionally, IARC’s 2016 review concluded that research consistently suggests no association between coffee consumption and risk of prostate cancer1.
- A 2011 meta-analysis found that coffee drinkers had a 21% lower risk of developing prostate cancer than non-coffee drinkers (relative risk 0.79)5
- A 2011 prospective analysis of 47,911 men in the Health Professionals Follow-up Study, 5,035 of which had prostate cancer, observed a strong inverse association between coffee consumption and risk of advanced prostate cancer. Men who consumed 6 or more cups of coffee per day had a 60% lower risk of lethal and advanced prostate cancer than non-drinkers. The association appeared to be related to the non-caffeine components of coffee, as the association with lethal cancer was similar for regular and decaffeinated coffee66
- A 2014 meta-analysis suggested that coffee consumption has a protective effect on prostate cancer, concluding that coffee consumption may be inversely associated with the risk of fatal prostate cancer, but showed no clear evidence of an association with its incidence67
- Three further meta-analyses in 2014 also supported the hypothesis that coffee consumption may decrease the risk of prostate cancer68-70. One suggested a significant inverse relationship for fatal prostate cancers and high-grade prostate cancers66, whilst a second suggested that intakes of coffee greater than 4 or 5 cups per day may be associated with a reduced risk of overall prostate cancer, as well as fatal and high-grade prostate cancers68
- A 2015 meta-analysis concluded that coffee consumption may be associated with a reduced risk of prostate cancer, particularly amongst European populations, and observed an inverse association with non-advanced prostate cancer71
- A 2021 systematic review and meta-analysis suggested that a higher intake of coffee may be associated with a lower risk of prostate cancer. The authors concluded that compared with the lowest coffee intake category, there was a 9% reduction in the risk of prostate cancer for the highest category72