Colorectal cancer (CRC) is one of the most commonly diagnosed malignancies worldwide and remains a major cause of cancer-related mortality. Increasing attention has therefore been directed towards modifiable dietary factors that may influence colorectal carcinogenesis and outcomes after diagnosis. Coffee is of particular interest because it contains numerous biologically active compounds that can interact with molecular, metabolic, inflammatory, and microbial pathways implicated in colorectal tumorigenesis. Epidemiological and experimental evidence suggests that coffee consumption may be associated with favourable CRC outcomes, although the mechanisms underlying these associations remain incompletely understood.
Coffee contains several bioactive constituents, including caffeine, chlorogenic acids, polyphenols, diterpenes, melanoidins, and other antioxidant compounds. The potential biological effects of coffee are therefore unlikely to be attributable to a single constituent. Experimental studies suggest that coffee and its major bioactive compounds may influence oxidative stress, inflammatory signalling, cell proliferation, apoptosis, cellular metabolism, and the intestinal microbiome. These effects provide a biological rationale for a potential protective role of coffee in colorectal carcinogenesis (Romualdo et al.; Bułdak et al.).
Antioxidant effects and protection against oxidative damage
Oxidative stress contributes to colorectal carcinogenesis by promoting DNA damage, genomic instability, lipid peroxidation, and alterations in cellular signaling. Coffee contains chlorogenic acids and other polyphenolic compounds with antioxidant properties that may reduce oxidative stress and influence endogenous antioxidant defense mechanisms. Coffee-derived compounds may also modulate redox-sensitive signaling pathways involved in cellular proliferation, survival, and inflammatory responses.
These effects may be particularly relevant to the colonic epithelium, which is continuously exposed to dietary and microbial metabolites. By reducing oxidative damage and modifying cellular responses to oxidative stress, coffee constituents may potentially reduce the accumulation or persistence of molecular alterations associated with malignant transformation.
Modulation of inflammation and tumor-promoting signaling
Chronic inflammation contributes to colorectal tumorigenesis by promoting epithelial injury, cellular proliferation, angiogenesis, and tumor progression. Coffee and its bioactive compounds have demonstrated anti-inflammatory effects in experimental models and may influence signaling pathways involved in inflammatory mediator production.
Caffeine may exert some of these effects through modulation of adenosine receptors, which participate in inflammatory and immune responses. Downstream signalling pathways, including PI3K/AKT/mTOR and MAPK-related pathways, have also been investigated as potential targets of caffeine and other coffee constituents. Modulation of these pathways may influence inflammatory responses, cell survival, proliferation, and tumor-cell behavior.
Inhibition of cell proliferation and induction of apoptosis
Another potential mechanism involves direct effects of coffee constituents on colorectal epithelial and tumor cells. Experimental studies have reported inhibition of tumor-cell proliferation and induction of apoptosis following exposure to coffee or individual compounds such as caffeine and chlorogenic acids.
These effects may involve cell-cycle regulation, mitochondrial pathways, and modulation of intracellular survival and apoptotic signaling. Caffeine has also been investigated for effects on DNA damage responses and pathways regulating cell-cycle progression. By limiting uncontrolled proliferation and promoting the elimination of damaged or transformed cells, these mechanisms could theoretically reduce tumor initiation and progression (Bułdak et al.; Sang et al.).
However, concentrations of individual compounds used in experimental models may not correspond to concentrations achieved through habitual coffee consumption in humans. Therefore, experimental findings should be interpreted as providing mechanistic plausibility rather than direct evidence of clinical anticancer efficacy.
Effects on glucose metabolism and insulin signaling
Metabolic abnormalities, particularly insulin resistance and hyperinsulinemia, have been implicated in colorectal carcinogenesis. Coffee consumption has been associated with favorable effects on insulin sensitivity and glucose metabolism, although these effects are not specific to CRC.
Improved metabolic regulation could potentially influence colorectal tumor biology through reduced exposure to hyperinsulinemia and altered insulin-related signaling. Both caffeine and non-caffeine components may contribute to the metabolic effects of coffee. Thus, metabolic modulation represents a possible indirect pathway through which habitual coffee consumption could influence colorectal cancer development and progression.
Modulation of the gut microbiome
The gut microbiome represents another potentially important pathway linking coffee consumption with colorectal cancer. Intestinal microorganisms influence epithelial integrity, immune responses, inflammation, microbial metabolite production, and host metabolism, all of which can affect colorectal carcinogenesis.
Coffee-derived polyphenols and other compounds reach the gastrointestinal tract, where they can be metabolized by intestinal microorganisms. At the same time, coffee consumption may alter the composition and activity of the gut microbiota. Human studies have reported associations between long-term coffee consumption and differences in fecal microbial composition, supporting the possibility that coffee acts as a dietary modulator of the intestinal microbial ecosystem.
Such microbiome changes could influence the production of microbial metabolites, intestinal inflammation, epithelial barrier function, and host immune responses. The potential anticancer effects of coffee may therefore involve a bidirectional interaction between coffee constituents and the gut microbiota rather than direct effects on tumor cells alone.
An integrated mechanism of potential protection
The potential relationship between coffee consumption and CRC is likely to involve several interconnected pathways. Coffee polyphenols and other compounds may reduce oxidative stress and inflammatory signaling, while caffeine and other constituents may influence adenosine receptor activity, cell-cycle regulation, apoptosis, and intracellular signaling. Coffee may also influence systemic metabolic pathways and modify the intestinal microbiome.
These effects could create a biological environment that is less favorable to colorectal carcinogenesis. Reduced oxidative stress may limit DNA damage, attenuation of inflammatory signaling may reduce a tumor-promoting microenvironment, inhibition of abnormal proliferation may restrict tumor growth, and induction of apoptosis may facilitate the removal of damaged cells. Concurrent effects on glucose metabolism and the gut microbiome could further influence the intestinal and systemic environment.
Clinical relevance
The proposed mechanisms are supported by observational evidence linking coffee consumption with favourable CRC outcomes. Studies in patients with stage III colon cancer and stage I–III CRC have reported associations between higher coffee consumption and longer disease-free survival or lower mortality. Similar associations have been reported among patients with advanced or metastatic CRC. However, these studies are observational and cannot establish that coffee consumption itself causes improved outcomes.
The consistency between experimental findings and epidemiological observations provides biological plausibility for a potential protective association, but differences in coffee composition, preparation, quantity, caffeine content, dietary patterns, metabolic characteristics, and gut microbiota may influence individual responses.
Conclusion
Coffee contains multiple bioactive compounds that may influence biological processes relevant to colorectal carcinogenesis. Potential mechanisms include reduction of oxidative stress, modulation of inflammatory signalling, inhibition of tumour-cell proliferation, induction of apoptosis, effects on metabolic pathways, and alteration of the gut microbiome. These mechanisms may act together to influence the initiation and progression of colorectal cancer.
Although observational studies have reported associations between coffee consumption and favourable CRC outcomes, causality has not been established. Coffee should therefore be considered a potentially relevant dietary factor with plausible biological effects rather than an established preventive or therapeutic intervention for CRC.
References
- Romualdo GR, Rocha AB, Vinken M, Cogliati B, Moreno FS, Chaves MAG, et al. Drinking for protection? Epidemiological and experimental evidence on the beneficial effects of coffee or major coffee compounds against gastrointestinal and liver carcinogenesis. Food Res Int. 2019;123:567-589.
- Bułdak RJ, Hejmo T, Osowski M, Bułdak Ł, Kukla M, Polaniak R, et al. The impact of coffee and its selected bioactive compounds on the development and progression of colorectal cancer in vivo and in vitro. Molecules. 2018;23(12):3309.
- Sang LX, Chang B, Zhang WL, Wu XM, Li XH, Jiang M. Caffeine and its main targets of colorectal cancer. World J Gastrointest Oncol. 2020;12(2):149-161.
- González S, Salazar N, Ruiz-Saavedra S, Gómez-Martín M, de los Reyes-Gavilán CG, Gueimonde M. Long-term coffee consumption is associated with fecal microbial composition in humans. Nutrients. 2020;12(5):1287.