Given the popularity of coffee worldwide, it is unsurprising that it is a highly researched topic regarding health outcomes, including its relationship to cancer. In 2016, the International Agency for Research on Cancer (IARC) updated its 1991 statement that coffee is possibly carcinogenic to humans to “not classifiable as to its carcinogenicity to humans,” based on inadequate evidence of carcinogenicity, and the fact that most epidemiologic studies suggest a reduced risk for many cancers.
Several meta-analyses of epidemiologic studies suggest that coffee consumption is associated with a decreased risk of all-cause mortality and is not associated with cancer-related mortality.2-5 Several meta-analyses also suggest that coffee consumption may decrease the risk of many types of cancers, but for some cancers, the data remain mixed or indicate an increased risk.
Digestive Tract Cancers
A meta-analysis that included over 3 million patients from 15 case-control and cohort studies found that high levels of coffee consumption significantly decreased the risk of oral cancer compared with low levels of use (odds ratio [OR], 0.63; 95% CI, 0.52-0.75), with the association remaining among both case-control and cohort studies.6 A meta-analysis of laryngeal cancer, however, suggested that coffee consumption significantly increased cancer risk compared with non-coffee drinkers (RR, 1.47; 95% CI, 1.03-2.11), though a subgroup analysis showed that this association was significant among Europeans (RR, 1.63; 95% CI, 1.01-2.61) but not for the Americas (RR, 1.18; 95% CI, 0.7-1.99).7 Another meta-analysis found no association between coffee consumption and esophageal cancer, though a subgroup analysis found a decreased risk among an East Asian cohort (OR, 0.64; 95% CI, 0.44-0.83).
The association between coffee consumption and gastric cancer is less clear, with several meta-analyses suggesting an increased risk for some populations. Overall, the meta-analyses indicate no increased risk of gastric cancer with coffee consumption, even among groups who drank at least 3 cups per day.
For the United States population, however, 2 meta-analyses suggested an increased risk for gastric cancer. One analysis included 13 prospective cohort studies and 20 independent reports that encompassed 3368 cases of gastric cancer with a follow-up period ranging from 4.3 to 8.0 years. For the United States cohort, high levels of coffee consumption were significantly associated with an increased risk of gastric cancer (RR, 1.36; 95% CI, 1.06-1.75).11 The second analysis included 15 prospective cohort studies with 2019 cases of gastric cancer with a follow-up period ranging from 8 to 18 years.12 In the United States cohort, the risk of gastric cancer was significantly higher with 6.5 cups per day or more (RR, 1.36; 95% CI, 1.05-1.75).
Several studies indicate that coffee consumption is not associated with the risk of colorectal cancer, and may decrease risk with 4 or 5 cups per day.15,17 A meta-analysis of 19 prospective cohort studies that included over 2 million patients demonstrated that for every 4 cups of coffee per day, colon cancer risk was reduced by 7% (RR, 0.93; 95% CI, 0.88-0.99).15 An analysis of the
CALGB 89803 (ClinicalTrials.gov Identifier: NCT00003835) study of 953 patients with stage III colon cancer undergoing adjuvant chemotherapy found that consuming at least 4 cups of coffee per day reduced the risk of colon cancer recurrence or mortality (hazard ratio [HR], 0.58; 95% CI, 0.34-0.99) compared with never drinkers.There was no association between nonherbal teas or decaffeinated coffee.
Genitourinary and Reproductive Cancers
Several meta-analyses demonstrate that coffee consumption is not associated with breast, endometrial, ovarian, bladder, or kidney cancers.18-24 Most studies suggest that coffee consumption decreases the risk of prostate cancer by 10% to 53%.
Meta-analyses suggest that caffeinated coffee consumption decreases the risk of developing skin cancer, particularly basal cell carcinoma and melanoma.28-31 A meta-analysis that included over 37,000 nonmelanoma skin cancer cases demonstrated that high levels of coffee consumption significantly decreased the risk of disease compared with low consumption levels (RR, 0.82; 95% CI, 0.75-0.89), which was attributed to basal cell carcinoma.
There was no association with decaffeinated coffee or tea. A meta-analysis that included over 927,000 patients found that regular coffee consumption significantly reduced the risk of melanoma compared with controls (RR, 0.75; 95% CI, 0.63-0.89), but there was no association with decaffeinated coffee.30 Another meta-analysis, which included nearly 900,000 patients, demonstrated that high levels of coffee consumption significantly decreased the risk of melanoma (RR, 0.81; 95% CI, 0.68-0.97) compared with the lowest level of intake, and there was no association with decaffeinated coffee.
Meta-analysis found no association between coffee consumption and cancers of the thyroid, pancreas, and adult glioma.
In a meta-analysis of 8 prospective cohort studies and 13 case-control studies, coffee consumption increased the risk of lung cancer compared with nondrinkers (RR, 1.09; 95% CI, 1.00-1.19), but was not adjusted for smoking status. There was no association between coffee consumption and lung cancer among never smokers. Another meta-analysis, which included 17 studies, also found an increased risk of lung cancer among those who consumed coffee compared with nondrinkers (OR, 1.17; 95% CI, 1.03-1.33), particularly for those who drank high levels of coffee compared with low consumption levels (OR, 1.31; 95% CI, 1.11-1.55), though these associations were attributed to case-control studies and not cohort studies, and were present among men but not women.
The risk of liver cancer, however, was reduced with coffee consumption. A meta-analysis of 12 studies demonstrated a 44% decrease in risk of hepatocellular carcinoma with regular coffee consumption (RR, 0.66; 95% CI, 0.55-0.78) and by 50% with high levels of consumption (RR, 0.50; 95% CI, 0.43-0.58) compared with no or occasional consumption. Another meta-analysis found a similar reduction in liver cancer risk with high levels of coffee consumption compared with no or occasional consumption (RR, 0.55; 95% CI, 0.44-0.67).
Maternal consumption of coffee, regardless of the amount, was associated with an increased risk of childhood leukemias. In one study, any maternal coffee consumption during pregnancy significantly increased the risk of acute leukemia (OR, 1.22; 95% CI, 1.04-1.43), including acute lymphoblastic leukemia (OR, 1.65; 95% CI, 1.28-2.12) and acute myeloid leukemia (OR, 1.58; 95% CI, 1.20-2.08). Another meta-analysis found similar results, with high maternal coffee consumption during pregnancy increasing the risk of childhood ALL (OR, 1.43; 95% CI, 1.22-1.68) and AML (OR, 2.52; 95% CI, 1.59-3.57). In this study, tea was not associated with leukemia.
Most meta-analyses conclude that coffee consumption is not associated with an increased risk of cancer across many subtypes. Some studies noted a decreased risk of oral, colorectal, prostate, skin, and liver cancers with regular or high levels of coffee consumption. However, an increased risk of gastric cancers only among US populations, and a small increased risk of lung cancer, though the data are not of high quality, considering potential confounders and inconsistent results. Consumption of coffee during pregnancy may increase the risk of childhood leukemias.
Based on these data, it is unlikely that coffee consumption, even at high levels, increases the risk of cancer, and may be protective against certain cancer subtypes. Maternal consumption during pregnancy, however, should be avoided.
Source: (cancertherapyadvisor.com by Andrea S. Blevins Primeau, PhD, MBA)