Maté drinking and esophageal squamous cell carcinoma in South America: pooled results from two large multicenter case-control studies.

Background: Maté tea is a nonalcoholic infusion widely consumed in southern South America, and may increase risk of esophageal squamous cell carcinoma (ESCC) and other cancers due to polycyclic aromatic hydrocarbons (PAH) and/or thermal injury. Methods: We pooled two case–control studies: a 1988 to 2005 Uruguay study and a 1986 to 1992 multinational study in Argentina, Brazil, Paraguay, and Uruguay, including 1,400 cases and 3,229 controls. We computed ORs and fitted a linear excess OR (EOR) model for cumulative maté consumption in liters/day–year (LPDY). Results: The adjusted OR for ESCC with 95% confidence interval (CI) by ever compared with never use of maté was 1.60 (1.2–2.2). ORs increased linearly with LPDY (test of nonlinearity; P = 0.69). The estimate of slope (EOR/LPDY) was 0.009 (0.005–0.014) and did not vary with daily intake, indicating maté intensity did not influence the strength of association. EOR/LPDY estimates for consumption at warm, hot, and very hot beverage temperatures were 0.004 (−0.002–0.013), 0.007 (0.003–0.013), and 0.016 (0.009–0.027), respectively, and differed significantly (P < 0.01). EOR/LPDY estimates were increased in younger (<65) individuals and never alcohol drinkers, but these evaluations were post hoc, and were homogeneous by sex. Conclusions: ORs for ESCC increased linearly with cumulative maté consumption and were unrelated to intensity, so greater daily consumption for shorter duration or lesser daily consumption for longer duration resulted in comparable ORs. The strength of association increased with higher maté temperatures. Impact: Increased understanding of cancer risks with maté consumption enhances the understanding of the public health consequences given its purported health benefits. Cancer Epidemiol Biomarkers Prev; 23(1); 107–16. ©2013 AACR.


Introduction
Maté tea is an infusion made from leaves of the tree Ilex paraguariensis, a member of the Aquifoliaceae (holly) family (1,2). It is a non-alcoholic beverage consumed throughout southern South America, and is gaining broader acceptance in other areas of the world as a tea and dietary supplement based on purported health benefits, such as lowered cholesterol levels, improved cardiovascular health and obesity management (2,3). However, studies have linked maté consumption with esophageal squamous cell carcinoma (ESCC), as well as cancers of the oral cavity, pharynx, larynx, lung, kidney and bladder (4)(5)(6)(7)(8)(9)(10)(11)(12)(13). The International Agency for Research on Cancer (IARC) designated hot maté drinking a probable human carcinogen (group 2A) (1). Proposed carcinogenic mechanisms include thermal injury from repeated high temperature exposure and exposure to polycyclic aromatic hydrocarbons (PAHs), a productionrelated contaminant (1,(14)(15)(16)(17).
While studies have associated maté consumption with ESCC, there has been no quantitative evaluation of the relationship between ESCC and total exposure, as measured by liters/day-year (LPDY), the product of lifetime mean liters/day (LPD) and years of consumption.
In addition, evaluations of potential effect modifiers, such as age, sex, cigarette smoking and alcohol consumption, have been limited.
We pooled data from two large case-control studies of ESCC, one an aggregation of five component studies. Our goals were to evaluate: (i) the quantitative relationship between ESCC and LPDY of maté consumption; (ii) the impact of LPD on the strength of association; and (iii) potential effect modifiers, including maté temperature, sex, age, cigarette smoking and alcohol consumption.

Study data
Uruguay case-control study (5) Cases included patients who were incident between 1990-2004, aged 35-85 years in medical records of the Oncology Institute Cancer Registry with histopathologically confirmed ESCC. Patients had to be mentally competent for interview, diagnosed within the previous four months and resident in Uruguay for ≥10 years.
Controls included patients admitted to the same institution during the same period with conditions unrelated to tobacco smoking and alcohol consumption and with comparable residency, and were frequency matched to cases by age and sex. Within the frequency matched groups, investigators enrolled greater numbers of female controls.
Interviews occurred shortly after hospital admittance. Questionnaires collected information on demographic and socioeconomic characteristics, personal and family history, maté drinking, alcohol consumption and tobacco smoking. For alcohol intake, we calculated milliliters (ml) of ethanol/day by summing ethanol/day for a standard serving of each beverage type.
International Agency for Research on Cancer (IARC) Multinational Case-Control Study (4,18) Between 1986 and 1992, investigators conducted four hospital-based case-control studies of ESCC in Argentina, Brazil, Paraguay and Uruguay, the latter independent of the Uruguay Study described above. Investigators further extended this Uruguay component, which represented a fifth study. IARC coordinated the studies, which we have collectively denoted as the IARC Multinational Study. Results have been published previously (4,(18)(19)(20)(21)(22)

Statistical methods
For categorical variables, we computed odds ratios (OR) using standard logistic regression (23). For continuous LPDY, d, ORs were not log-linear. We thus fitted the model z was a vector of adjustment variables with parameters α, while β was the excess odds ratio per LPDY (EOR/LPDY), a measure of strength of association. We replaced d with d×exp{θ ln(d)}=d 1 + θ and used the likelihood ratio to test no departure from linearity (θ=0).
We evaluated effect modification by examining variations in the trend of ORs by LPDY across a categorical factor (f). For factor f with S categories, s=1,…,S, we fitted where β s parameters replaced β and d s equaled d within category s and zero otherwise. If f was unrelated to maté consumption, e.g., sex, then z included f as an adjustment variable. If f was related to maté consumption, e.g., LPD or beverage temperature, then z did not include f since no adjustment in never-drinkers was required. We compared deviances for model (1) and model (2) to test homogeneity of slopes, β 1 =…= β S = β, i.e., no effect modification. We replaced d s with d s ×exp{θ s ln(d s )} to test no departure from linearity within category (θ s =0).
We used the Epicure program to estimate ORs and 95% confidence intervals (CI), fit models and derive likelihood-based CIs for β estimates (24). for the Uruguay Study income (< US$120, ≥US$120, missing) and residency (urban, rural).
ORs by LPDY increased linearly in the IARC data and in the Uruguay data, but only among maté drinkers in the latter. For Uruguay data, we defined a fixed offset to adjust for ever and never maté drinkers using the model OR(d) = exp{α I(d)}×{1 + β d}, where I(d) equaled one for d>0 and zero otherwise. The estimate, exp{α}, was 2.42 (95% CI, 1.5, 2.9), and represented the LPDY-adjusted OR of ever relative to never consumed maté. A detailed examination identified a small subgroup responsible for the excess. The subgroup included male (3 cases and 53 controls) and female (1 case and 61 controls) urban residents who abstained from alcohol, with ORs for ever consumed maté of 4.24 (1.1, 16.7) and 13.8 (1.8, 105.8), respectively. We fixed the offset to −ln(4.24) and −ln(13.8) for Uruguay male and female urban residents who never consumed alcohol or maté and zero otherwise. The offset essentially served to replace the observed case to control odds with the expected odds, eliminating the non-linearity. See details in Supplemental Material and comments in the Discussion. The use of a fixed offset was an a priori decision, due to a concern about the possibility of broad impact on ORs from this small, highly influential subgroup. Alternatively, we could have introduced an indicator variable for this subgroup and estimated its effect, or have omitted these subjects. Regardless of approach, inference was unaffected.

Odds ratios for adjustment and other factors
There were 1,400 cases (1,085 males and 315 females) and 3,229 controls (2,279 males and 950 females) ( Table 1). ORs increased with pack-years of smoking, cigarettes/day, cumulative alcohol consumption and alcohol intensity in both studies (P<0.01). ORs increased with use of mixed/black-only tobacco cigarettes compared to blond-only tobacco cigarettes, achieving statistical significance in the IARC Study and the pooled data. We evaluated ORs by self-reported maté temperature, warm, hot or very hot, and found that ORs increased significantly with temperature, although the OR for warm maté consumption was not statistically significant. Few users ceased consumption (8.4% and 12.0% in Uruguay and IARC controls, respectively) and ORs varied inconsistently with years since cessation.

Marginal odds ratios for maté consumption
Among drinkers, ORs were increased at younger age at first use in the Uruguay data and unrelated in the IARC data.
OR trends were homogeneous across studies for maté temperature (p=0.85) and cessation (p=0.84), but differed for cumulative intake, intensity and age at first use (p<0.01) (not shown).

Joint odds ratios for cumulative liters/day-years and liters/day of maté consumption
We first examined LPD as a modifier of the LPDY association, i.e., whether the strength of association varied by intensity or alternatively whether for a fixed total LPDY low intensity for long duration resulted in greater, equal or lesser risk compared to high intensity for short duration. For joint categories of LPDY and LPD, ORs relative to never drinkers increased with LPDY within each LPD category (

Effect modification of the association of cumulative maté use
There was significant variation of EOR/LPDY estimates with temperature, years since maté cessation and age at first consumption (P<0.01) ( Table 3). The EOR/LPDY estimates increased with temperature, 0.004 (-0.002,0.013), 0.007 (0.003,0.013) and 0.016 (0.009,0.027) for warm, hot and very hot consumers, respectively. In warm maté consumers, ORs by LPDY categories increased monotonically; however, the test of no trend did not reject (P=0.14).
Adjusted for study differences, variations in EOR/LPDY patterns across the potential modifiers were consistent for the studies, and tests of homogeneity of effect modification did not  Table B2 Moreover, maté intensity did not alter the linear association with LPDY, suggesting that the main determinant of risk was cumulative intake and that for a given intake, higher intensity consumption for shorter duration or lower intensity consumption for longer duration resulted in comparable ORs. We could not however rule out an enhanced association in low (<0.5 LPD) intensity drinkers, although this enhancement may have reflected differential misclassification, with lower maté intensity cases underreporting cumulative intake.
Although estimates of the association have varied, increased ORs with beverage temperature are observed in many countries and across diverse beverage types (15). Intra-esophageal temperatures are sensitive to initial fluid temperature, time between sips and sip volume, suggesting substantial inherent variability (28,29). Moreover, temperatures were self-assessed, further increasing misclassification. In spite of the substantial misclassification, the strength of association in the current analysis increased with temperature; EOR/LPDY estimates were 0.004, 0.007 and 0.016 for consumption at warm, hot and very hot temperatures, respectively (Table 3), consistent with thermal injury damaging the epithelial lining of the esophagus and thereby directly affecting risk or enabling other factors. Experimental animal studies involving high temperature liquids support this pattern (30)(31)(32). Nonetheless, risks for warm maté drinkers remain uncertain. While category-specific ORs increased monotonically, the test of no trend was not rejected (P=0.14).
Although there have been relatively few studies and results to date are not conclusive, studies have associated maté consumption with diverse cancer sites, including oral cavity, pharynx, larynx, lung, kidney and bladder (4-12, 16). Thus, the etiology of ESCC may potentially involve maté-associated non-thermal factors. Attention has focused on PAHs, in particular benzo[a]pyrene (BaP), a possible production-acquired contaminate (16, 33), which IARC has classified as a human carcinogen (34,35). Since cigarette smoke contains PAHs, residual confounding may have influenced maté-related ORs (2,8). However, substantial confounding in the current analysis seems unlikely, since among users the Pearson correlation between liters/day of maté and cigarettes/day was small (0.11 in controls), urinary measurements of 1-hydroxypyrene glucuronide, a stable PAH metabolite, correlated positively with maté consumption (14) and, importantly, we observed significant trends in ORs with LPDY in never smokers and in smokers after extensive smoking adjustment.
Conclusions were not definitive regarding modification by other maté-related variables. Cessation of maté drinking significantly modified EOR/LPDY estimates (P<0.01); however, the largest estimate occurred in recent (1-4 years) former drinkers (=0.020), with lower estimates in both current (=0.009) and long-term (≥5 years) former drinkers (=0.005) ( Table 3). Because prodromal symptoms may have influenced responses, we recalculated EOR/LPDY for <5 and ≥5 years cessation and found estimates of 0.009 and 0.006, respectively, indicating reduced maté effects with increased cessation (P<0.01). This result agreed with two previous studies that found higher ORs in former compared to current drinkers (4, 7), but not another which found monotonically decreasing ORs with cessation (13). Our analyses were necessarily limited due to few long-term quitters (74 cases and 167 controls). Younger ages at initiation increased the strength of the LPDY association; however, interpretation was problematic since variations in EOR/LPDY estimates were inconsistent across studies (P<0.01) (Table B2).
Cumulative maté effects were statistically homogeneous by sex for each study and the pooled data; however, category-specific ORs with LPDY and EOR/LPDY estimates were greater in females. These results corresponded to previous findings for the IARC Study (4). Although not significant, consistency in the enhanced effects in females suggested the need for further evaluation in other study populations.
No definitive conclusions were possible for the roles of age, cigarette smoking and alcohol as effect modifiers. The largest EOR/LPDY estimate occurred for ages <65 years in each study and in the pooled data (Table C2); however, homogeneity of EOR/LPDY estimates was not rejected (P=0.14). Only under post hoc evaluation did EOR/LPDY estimates vary significantly for ages <65 years. In the pooled data, smoking status and type of tobacco were significant modifiers of the maté association, but higher LPDY consumers drove results. For for never, former and current smokers, respectively, and homogeneous (P=0.32), which was concordant with a previous result (13). Estimates were -0.002, 0.013, 0.020 in never smokers, blond-only, mixed/black-only tobacco users (P=0.22). Finally, while ORs and the EOR/LPDY estimate were greatest in those who never consumed alcohol and homogeneity was not statistically rejected (P=0.12), the differential EOR/LPDY estimates occurred only in the IARC Study ( Table 2).

Initial analyses revealed that ORs by LPDY increased linearly in both the IARC and
Uruguay datasets, with linearity in the latter dataset occurring only in maté consumers. While maté-related ORs could vary in populations due to different methods of preparation and consumption, trends with consumption should be roughly comparable. Exploratory analysis of the Uruguay dataset identified a small subgroup of urban residents who never consumed alcohol (4 cases and 114 controls) with significant ORs by ever consumed maté of 4.2 for males and 13.8 for females. The inclusion of a fixed offset eliminated non-linearity in the Uruguay data. An alternative approach could have specified a non-linear relationship for ORs with LPDY in the Uruguay data, and derived an offset for the IARC data that induced a curvilinear pattern to mimic the Uruguay data. We did not apply this approach, since it increases model complexity and since linearity typically represents the preferred first order approximation (Occam's Razor).
A second alternative could have omitted the offset and used a combined linear relationship for the IARC data and a curvilinear relationship for the Uruguay data. Under this approach, the inference in Table 3 was largely unchanged, except EOR/LPDY variations were not significant for attained age (P=0.87 and P=0.63 for post hoc categories of ages <65 and ≥65) but were significant for alcohol status (P<0.01) (not shown).
In summary, our results confirmed the hypothesis that drinking maté increases risk of ESCC, with ORs consistent with a linear relationship in cumulative intake. Moreover, the strength of association with cumulative intake was not influenced by consumption intensity, so that greater daily consumption for a shorter duration or less daily consumption for a longer duration resulted in comparable ORs. The increased ORs also occurred at all beverage temperatures, but were greater with higher mate temperatures.   <0.01 0.55 <0.01 a ORs from logistic regression for the mate consumption variable, adjusted by smoking (pack-years, cigarettes/day), alcohol consumption (drink-years, drinks/day), age, sex, sex by education and for Uruguay income and urban/rural residence. Pooled ORs further adjusted for study. Models included a sex-specific fixed offset variable for the Uruguay data to account for differential effects of mate consumption in urban, never alcohol consumers. Numbers of cases and controls differ slightly from Table 1 due to missing data. b Referent category, except where noted. Numbers of cases and controls vary due to missing data. c P-value for the score test of no trend. d ORs and P-values computed among mate drinkers only relative to the lowest category. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
Author Manuscript Published OnlineFirst on October 15, 2013; DOI: 10.1158/1055-9965.EPI-13-0796 a ORs adjusted for study, cigarette smoking (pack-years, cigarettes/day), alcohol consumption (drink-years, ml ethanol/day), age, sex, education and for Uruguay income and urban/rural residence. Models included a sexspecific fixed offset variable to account for differential effects of mate consumption in urban, never alcohol consumers for the Uruguay data. ORs relative to never mate consumers. b Estimated EOR/liter/day-year based on linear odds ratios for liter/day-years relative to never-drinkers within levels of a modifier: OR(d) = 1 + ∑ i γ i d i for the i th level, where d i and γ i are the cumulative LPDY and EOR/LPDY within the i th level, respectively. For all data, the EOR/LPDY estimate with 95% confidence interval was 0.009 (0.005, 0.14). c Likelihood-based 95 percent confidence interval (CI) for the EOR/LPDY. d P-value for test of homogeneity of EOR/LPDY across levels of the modifier. e Not estimable.