A dose-response meta-analysis of coffee consumption and bladder cancer

Coffee consumption, cancer, and healthy aging: epidemiological evidence and underlying mechanisms

This comprehensive review examines the role of coffee consumption in promoting healthy aging and its potential impact on cancer prevention. Previous research has shown that moderate coffee intake may contribute to extending healthspan and enhancing longevity through beneficial effects on cardiometabolic health and key biological processes involved in aging. However, the relationship between coffee consumption and cancer risk remains controversial. This review synthesizes longitudinal observational and interventional data on the effects of coffee consumption on overall and site-specific cancers, explores underlying biological mechanisms, and discusses clinical and public health implications. Additionally, the review highlights evidence from Mendelian randomization (MR) studies to assess potential causal relationships. Our findings suggest that coffee consumption is associated with a reduced risk of several cancers, including skin, liver, prostate, and endometrial cancers, and may also lower cancer recurrence rates, particularly in colorectal cancer. These protective associations appear consistent across different demographic groups, with the most significant benefits observed at consumption levels of three or more cups per day. However, evidence is inconclusive for many other cancers, and coffee consumption is consistently linked to an increased risk of lung cancer. MR studies generally do not support a strong causal relationship for most cancers, though some suggest potential protective effects for hepatocellular, colorectal, and possibly prostate cancers, with mixed results for ovarian cancer and an increased risk for esophageal cancer and multiple myeloma. The protective effect of coffee on liver and prostate cancer is supported by both observational and MR studies. The potential anti-cancer benefits of coffee are attributed to its bioactive compounds, such as caffeine, chlorogenic acids, and diterpenes, which possess antioxidant and anti-inflammatory properties. These compounds may reduce oxidative stress, inhibit cancer cell proliferation, induce apoptosis, and modulate hormone levels. The review emphasizes the need for further research to clarify dose-response relationships, causal associations, and the biological mechanisms underlying these associations. While coffee consumption appears to contribute to cancer prevention and healthy aging, caution is warranted due to the increased risk of certain cancers, highlighting the complexity of its health effects.

Caffeine as a Factor Influencing the Functioning of the Human Body-Friend or Foe?

Nowadays, caffeine is one of the most commonly consumed substances, which presents in many plants and products. It has both positive and negative effects on the human body, and its activity concerns a variety of systems including the central nervous system, immune system, digestive system, respiratory system, urinary tract, etc. These effects are dependent on quantity, the type of product in which caffeine is contained, and also on the individual differences among people (sex, age, diet etc.). The main aim of this review was to collect, present, and analyze the available information including the latest discoveries on the impact of caffeine on human health and the functioning of human body systems, taking into account the role of caffeine in individual disease entities. We present both the positive and negative sides of caffeine consumption and the healing properties of this purine alkaloid in diseases such as asthma, Parkinson's disease, and others, not forgetting about the negative effects of excess caffeine (e.g., in people with hypertension, children, adolescents, and the elderly). In summary, we can conclude, however, that caffeine has a multi-directional influence on various organs of the human body, and because of its anti-oxidative properties, it was, and still is, an interesting topic for research studies including those aimed at developing new therapeutic strategies.

Mutational Landscape and Environmental Effects in Bladder Cancer

Bladder cancer is the most common cancer of the urinary tract. Although nonmuscle-invasive bladder cancers have a good prognosis, muscle-invasive bladder cancers promote metastases and have a poor prognosis. Comprehensive analyses using RNA sequence of clinical tumor samples in bladder cancer have been reported. These reports implicated the candidate genes and pathways that play important roles in carcinogenesis and/or progression of bladder cancer. Further investigations for the function of each mutation are warranted. There is suggestive evidence for several environmental factors as risk factors of bladder cancer. Environmental factors such as cigarette smoking, exposure to chemicals and gases, bladder inflammation due to microbial and parasitic infections, diet, and nutrition could induce several genetic mutations and alter the tumor microenvironment, such as immune cells and fibroblasts. The detailed mechanism of how these environmental factors induce carcinogenesis and/or progression of bladder cancer remains unclear. To identify the relationship between the mutations and the lifestyle could be useful for prevention and treatment of bladder cancer.

Coffee consumption and risk of bladder cancer: a pooled analysis of 501,604 participants from 12 cohort studies in the BLadder Cancer Epidemiology and Nutritional Determinants (BLEND) international study

Recent epidemiological studies have shown varying associations between coffee consumption and bladder cancer (BC). This research aims to elucidate the association between coffee consumption and BC risk by bringing together worldwide cohort studies on this topic. Coffee consumption in relation to BC risk was examined by pooling individual data from 12 cohort studies, comprising of 2601 cases out of 501,604 participants. Pooled multivariate hazard ratios (HRs), with corresponding 95% confidence intervals (CIs), were obtained using multilevel Weibull regression models. Furthermore, dose-response relationships were examined using generalized least squares regression models. The association between coffee consumption and BC risk showed interaction with sex (P-interaction < 0.001) and smoking (P-interaction = 0.001). Therefore, analyses were stratified by sex and smoking. After adjustment for potential confounders, an increased BC risk was shown for high (> 500 ml/day, equivalent to > 4 cups/day) coffee consumption compared to never consumers among male smokers (current smokers: HR = 1.75, 95% CI 1.27-2.42, P-trend = 0.002; former smokers: HR = 1.44, 95% CI 1.12-1.85, P-trend = 0.001). In addition, dose-response analyses, in male smokers also showed an increased BC risk for coffee consumption of more than 500 ml/day (4 cups/day), with the risk of one cup (125 ml) increment as 1.07 (95% CI 1.06-1.08). This research suggests that positive associations between coffee consumption and BC among male smokers but not never smokers and females. The inconsistent results between sexes and the absence of an association in never smokers indicate that the associations found among male smokers is unlikely to be causal and is possibly caused by residual confounding of smoking.

Association between coffee consumption and risk of bladder cancer in a meta-analysis of 16 prospective studies

Background

Current evidence remains equivocal as to whether and how consumption of coffee may be associated with risk of bladder cancer, and potential influence of confounding by smoking on this association is yet to be elucidated. We conducted an updated meta-analysis of prospective studies to address these issues.

Methods

Relevant studies were identified by searching PubMed and EMBASE databases from inception to April 2019. A random-effects model was used to estimate summary relative risk (RR) with corresponding 95% confidence interval (CI) of bladder cancer associated with coffee consumption.

Results

The final analysis included 16 prospective studies comprising 2,122,816 participants and 11,848 bladder cancer cases. Overall, coffee consumption was not associated with risk of bladder cancer (RR _high-vs-low = 1.07, 95% CI: 0.96–1.20). The lack of association persisted in the strata defined by sex or participants’ smoking status. Meta-regression analyses identified the number cases (P_difference = 0.06) and the degree of adjustment for smoking (P_difference = 0.04) as potential sources of heterogeneity. There was an increased risk of bladder cancer related to higher coffee consumption among studies with fewer cases (RR _high-vs-low = 1.38, 95% CI: 1.05–1.81) and among those with poorer adjustment for smoking (RR _high-vs-low = 1.48, 95% CI: 1.14–1.93). Results were similar in the dose-response analyses (RR _{1 cup/d} = 1.01, 95% CI: 0.98–1.03).

Conclusion

Best evidence available to date does not support an independent association between coffee consumption and bladder cancer risk. Some direct associations observed in individual studies may be a result of residual confounding by smoking.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s12986-019-0390-3.

The association between coffee consumption and bladder cancer in the bladder cancer epidemiology and nutritional determinants (BLEND) international pooled study

Background

Inconsistent results for coffee consumption and bladder cancer (BC) risk have been shown in epidemiological studies. This research aims to increase the understanding of the association between coffee consumption and BC risk by bringing together worldwide case–control studies on this topic.

Methods

Data were collected from 13 case–control comprising of 5,911 cases and 16,172 controls. Pooled multivariate odds ratios (ORs), with corresponding 95% confidence intervals (CIs), were obtained using multilevel logistic regression models. Furthermore, linear dose–response relationships were examined using fractional polynomial models.

Results

No association of BC risk was observed with coffee consumption among smokers. However, after adjustment for age, gender, and smoking, the risk was significantly increased for never smokers (ever vs. never coffee consumers: OR_model2 1.30, 95% CI 1.06–1.59; heavy (> 4 cups/day) coffee consumers vs. never coffee consumers: OR_model2 1.52, 95% CI 1.18–1.97, p trend = 0.23). In addition, dose–response analyses, in both the overall population and among never smokers, also showed a significant increased BC risk for coffee consumption of more than four cups per day. Among smokers, a significant increased BC risk was shown only after consumption of more than six cups per day.

Conclusion

This research suggests that positive associations between coffee consumption and BC among never smokers but not smokers.

Coffee and tea drinking and risk of cancer of the urinary tract in male smokers

PURPOSE

We evaluated the association of coffee and tea drinking with risk of the urinary tract cancer in Finnish men, with high coffee consumption, using data from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study.

METHODS

The ATBC trial conducted from 1985 to 1993 enrolled 29,133 male smokers. We used Cox proportional hazards regression models to estimate hazard ratios (HRs) and confidence intervals (CIs), using men who drank more than 0 but less than 1 cup coffee/d and tea nondrinkers as our referent group for coffee and tea analyses, respectively.

RESULTS

During 472,402 person-years of follow-up, 835 incident cases of bladder cancer and 366 cases of renal cell carcinoma were ascertained. For bladder cancer, we observed no association for coffee consumption (HR ≥4 vs. >0 to <1 cups/d = 1.16, 95% CI = 0.86-1.56) and a borderline statistically significant inverse association for tea consumption (HR ≥1 vs. 0 cup/d = 0.77, 95% CI = 0.58-1.00). For renal cell carcinoma, we observed no association for coffee (HR ≥4 vs. >0 to <1 cups/d = 0.85, 95% CI = 0.55-1.32) or tea consumption (HR ≥1 vs. 0 cup/d = 1.00, 95% CI = 0.68-1.46). We found no impact of coffee preparation on coffee-cancer associations.

CONCLUSIONS

Coffee drinking was not associated with urinary tract cancers risk. Further research on tea and bladder cancer is warranted.

A Prospective Investigation of Coffee Drinking and Bladder Cancer Incidence in the United States

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

The association between coffee consumption and bladder cancer incidence in a pooled analysis of the Miyagi Cohort Study and Ohsaki Cohort Study

Recent epidemiological studies of the association between coffee consumption and the risk of bladder cancer have yielded conflicting results. The aim of the present study was to examine the association between coffee consumption and the incidence of bladder cancer on the basis of pooled data from two cohort studies carried out in Miyagi Prefecture, northeastern Japan. We delivered self-administered questionnaires inquiring about the frequency of coffee consumption and other lifestyle factors in 1990 for the Miyagi Cohort Study and in 1994 for the Ohsaki Cohort Study. We followed 73 346 individuals from both cohorts and identified 274 cases of bladder cancer during 17.6 years for the Miyagi Cohort Study and 13.3 years for the Ohsaki Cohort Study. The multivariate-adjusted hazard ratios (95% confidence intervals) of bladder cancer incidence for the individuals who drank coffee occasionally, 1-2 cups/day, and 3 or more cups/day compared with never drinkers were 1.22 (0.90-1.66), 0.88 (0.61-1.26), and 0.56 (0.32-0.99), respectively (Ptrend=0.04). The inverse association remained even after stratification for smoking status. These data indicate that there is a significant inverse association between coffee consumption and the risk of bladder cancer.

Coffee, Caffeine, and Health Outcomes: An Umbrella Review

To evaluate the associations between coffee and caffeine consumption and various health outcomes, we performed an umbrella review of the evidence from meta-analyses of observational studies and randomized controlled trials (RCTs). Of the 59 unique outcomes examined in the selected 112 meta-analyses of observational studies, coffee was associated with a probable decreased risk of breast, colorectal, colon, endometrial, and prostate cancers; cardiovascular disease and mortality; Parkinson's disease; and type-2 diabetes. Of the 14 unique outcomes examined in the 20 selected meta-analyses of observational studies, caffeine was associated with a probable decreased risk of Parkinson's disease and type-2 diabetes and an increased risk of pregnancy loss. Of the 12 unique acute outcomes examined in the selected 9 meta-analyses of RCTs, coffee was associated with a rise in serum lipids, but this result was affected by significant heterogeneity, and caffeine was associated with a rise in blood pressure. Given the spectrum of conditions studied and the robustness of many of the results, these findings indicate that coffee can be part of a healthful diet.

Modifiable risk factors for the prevention of bladder cancer: a systematic review of meta-analyses

Each year, 430,000 people are diagnosed with bladder cancer. Due to the high recurrence rate of the disease, primary prevention is paramount. Therefore, we reviewed all meta-analyses on modifiable risk factors of primary bladder cancer. PubMed, Embase and Cochrane database were systematically searched for meta-analyses on modifiable risk factors published between 1995 and 2015. When appropriate, meta-analyses (MA) were combined in meta-meta-analysis (MMA). If not, the most comprehensive MA was selected based on the number of primary studies included. Probability of causation was calculated for individual factors and a subset of lifestyle factors combined. Of 1496 articles identified, 5 were combined in MMA and 21 were most comprehensive on a single risk factor. Statistically significant associations were found for current (RR 3.14) or former (RR 1.83) cigarette smoking, pipe (RR 1.9) or cigar (RR 2.3) smoking, antioxidant supplementation (RR 1.52), obesity (RR 1.10), higher physical activity levels (RR 0.86), higher body levels of selenium (RR 0.61) and vitamin D (RR 0.75), and higher intakes of: processed meat (RR 1.22), vitamin A (RR 0.82), vitamin E (RR 0.82), folate (RR 0.84), fruit (RR 0.77), vegetables (RR 0.83), citrus fruit (RR 0.85), and cruciferous vegetables (RR 0.84). Finally, three occupations with the highest risk were tobacco workers (RR 1.72), dye workers (RR 1.58), and chimney sweeps (RR 1.53). The probability of causation for individual factors ranged from 4 to 68 %. The combined probability of causation was 81.8 %. Modification of lifestyle and occupational exposures can considerably reduce the bladder cancer burden. While smoking remains one of the key risk factors, also several diet-related and occupational factors are very relevant.

Association between green tea/coffee consumption and biliary tract cancer: A population-based cohort study in Japan

Green tea and coffee consumption may decrease the risk of some types of cancers. However, their effects on biliary tract cancer (BTC) have been poorly understood. In this population‐based prospective cohort study in Japan, we investigated the association of green tea (total green tea, Sencha, and Bancha/Genmaicha) and coffee consumption with the risk for BTC and its subtypes, gallbladder cancer, and extrahepatic bile duct cancer. The hazard ratios and 95% confidence intervals were calculated using the Cox proportional hazard model. A total of 89 555 people aged 45–74 years were enrolled between 1995 and 1999 and followed up for 1 138 623 person‐years until 2010, during which 284 cases of BTC were identified. Consumption of >720 mL/day green tea was significantly associated with decreased risk compared with consumption of ≤120 mL/day (hazard ratio = 0.67 [95% confidence interval, 0.46–0.97]), and a non‐significant trend of decreased risk associated with increased consumption was observed (P‐trend = 0.095). In the analysis according to the location of the primary tumor, consuming >120 mL green tea tended to be associated with decreased risk of gallbladder cancer and extrahepatic bile duct cancer. When Sencha and Bancha/Genmaicha were analyzed separately, we observed a non‐significant trend of decreased risk of BTC associated with Sencha but no association with Bancha/Genmaicha. For coffee, there was no clear association with biliary tract, gallbladder, or extrahepatic bile duct cancer. Our findings suggest that high green tea consumption may lower the risk of BTC, and the effect may be attributable to Sencha consumption.

Coffee consumption and the risk of incident gastric cancer--A meta-analysis of prospective cohort studies

As several epidemiological studies on the association of coffee consumption with gastric cancer risk have produced inconsistent results, this meta-analysis was designed to synthesize current evidence of this potential relationship. We searched PubMed, EMBASE, and the Cochrane Library up to September 2014 to retrieve relevant articles. Prospective cohort studies were included if the relative risks (RRs) or hazard ratios and 95% confidence intervals (CIs) for gastric cancer according to coffee consumption were reported. Fixed- or random-effects models were used based on heterogeneity. The search yielded 13 eligible cohort studies of 3484 incident gastric cancer patients from among 1,324,559 participants. A significantly increased risk was found between gastric cardia cancer and coffee consumption (RR = 1.50, 95% CI: 1.09-2.07). Compared with Europeans (RR = 1.12, 95% CI: 0.86-1.46) and Asians (RR = 0.96, 95% CI: 0.72-1.27), Americans (RR = 1.36, 95% CI: 1.06-1.74) demonstrated a significantly positive association. However, the significant differences of the pooled results vanished after adjusting for smoking or body mass index. Our meta-analysis results suggest that a high level of coffee consumption is a risk factor for gastric cancer. However, these results should not be overinterpreted because residual confounding effects of other factors could exist.

Induction of AhR-mediated gene transcription by coffee

Background

Aryl hydrocarbon receptor (AhR) is classically known to be activated by xenobiotics such as dioxins and polycyclic aromatic hydrocarbons (PAHs). Although it has been reported that PAHs are contained in roasted coffee beans, in general coffee beverages are not considered to be AhR activators. We tested whether exposure to coffee would activate AhR in cultured cells.

Methods

HepG2 cells stably expressing an AhR-responsive reporter gene were treated with coffee samples. Also, expression of CYP1A1, an endogenous AhR-responsive gene, was quantitated by RT-PCR and Western blotting in HepG2, Caco-2, and MCF-7 cells, after treatment with coffee. In order to obtain sensitive and reproducible results, all the experiments were performed with the cells placed in either phosphate-buffered saline (PBS) or pure serum, instead of routinely-used culture medium, whose intrinsic AhR-stimulating activity turned out to be so strong as to interfere with the analyses.

Results

All the coffee samples tested robustly stimulated AhR-mediated transcription in the reporter gene assays. Of note, to what extent coffee and other AhR agonists activated AhR was different, depending on whether the experiments were done in PBS or serum. CYP1A1 mRNA was induced by coffee, in HepG2, Caco-2, and MCF-7 cells placed in either PBS or serum. CYP1A1 protein expression, which was not detected in these cells incubated in PBS, was also increased by coffee in cells placed in serum.

Conclusions

By using culture medium-free experimental settings, we have shown that coffee is a strong AhR activator. Our observation may help elucidate as-yet-unrecognized effects of coffee on human health.

Coffee consumption and urologic cancer risk: a meta-analysis of cohort studies

OBJECTIVES

Controversial results were reported among several epidemiologic studies on the relationship between coffee consumption and urologic cancer risk. We, therefore, conducted this meta-analysis to clarify these associations.

METHODS

Electronic databases including Pubmed, Embase and Cochrane library were searched between January 1966 and August 2013 for eligible studies. Pooled relative risk (RR) and its 95 % confidence interval (CI) were calculated. All P values are two tailed.

RESULTS

Thirteen cohorts were eligible for inclusion. As to prostate cancer (PCa), significant reverse association was found among highest versus none/lowest analysis with acceptable heterogeneity (RR 0.86, 95 % CI 0.79-0.95; I(2) 25 %, P value for heterogeneity: 0.221). A pooled RR which assessed advanced PCa was 0.73 (with 95 % CI 0.50-1.07), and a slight stronger reverse association was found in fatal PCa. However, a slight insignificant reverse association, basing on 8 studies with 9 outcomes, was found in dose-response analysis (RR 0.98, 95 % CI 0.93-1.03). For kidney and bladder cancer, insignificant associations were found in both highest versus none/lowest analyses and dose-response analyses.

CONCLUSIONS

Our findings suggest that coffee consumption may reduce the risk of PCa. No associations were found with both bladder and kidney cancer. Further well-designed large-scaled cohort studies are warranted to provide more definitive conclusions.

Coffee and tea consumption are inversely associated with mortality in a multiethnic urban population

Coffee and tea are commonly consumed beverages. Inverse associations with mortality have been suggested for coffee and tea, but the relationships with cause-specific mortality are not well understood. We examined regular and decaffeinated coffee and tea in relation to mortality due to all causes, vascular, nonvascular, and cancer in the multi-ethnic, prospective, population-based Northern Manhattan Study. The study population included 2461 participants with diet data who were free of stroke, myocardial infarction, and cancer at baseline (mean age 68.30 ± 10.23 y, 36% men, 19% white, 23% black, 56% Hispanic). During a mean follow-up of 11 y, we examined the associations between coffee and tea consumption, assessed by food frequency questionnaire, and 863 deaths (342 vascular related and 444 nonvascular including 160 cancer deaths) using multivariable-adjusted Cox models. Coffee consumption was inversely associated with all-cause mortality [for each additional cup/d, HR = 0.93 (95% CI: 0.88, 0.99); P = 0.02]. Caffeinated coffee was inversely associated with all-cause mortality, driven by a strong protection among those who drank ≥4 cups/d. An inverse dose-response relationship between tea and all-cause mortality was suggested [for each additional cup/d, HR = 0.91 (95% CI: 0.84, 0.99); P = 0.01]. Coffee consumption ≥4/d was protective against nonvascular death [vs. <1/mo, HR = 0.57 (95% CI: 0.33, 0.97)] and tea consumption ≥2/d was protective against nonvascular death [HR = 0.63 (95% CI: 0.41, 0.95)] and cancer [HR = 0.33 (95% CI: 0.14, 0.80)]. There was a strong inverse association between coffee and vascular-related mortality among Hispanics only. Further study is needed, including investigation into the mechanisms and compounds in coffee and tea responsible for the inverse associations with mortality. The differential relationship between coffee and vascular death across race/ethnicity underscores the need for research in similar multi-ethnic cohorts including Hispanics.