By David Kiefer, MD
Clinical Assistant Professor, Department of Family Medicine, University of Wisconsin; Clinical Assistant Professor of Medicine, Arizona Center for Integrative Medicine, University of Arizona, Tucson
Dr. Kiefer reports no financial relationships relevant to this field of study.
SYNOPSIS: In a cohort of more than 50,000 people, there was a higher risk of esophageal squamous cell carcinoma in those who consumed higher quantities of mostly black tea at hotter temperatures.
SOURCE: Islami F, Poustchi H, Pourshams A, et al. A prospective study of tea drinking temperature and risk of esophageal squamous cell carcinoma. Int J Cancer 2019; Mar 20. doi: 10.1002/ijc.32220. [Epub ahead of print].
For many of us, warm beverage consumption is an important routine to start our day or stave off the chilling effects of those long winter days. Drinking teas (infusions) and coffee is pan-cultural; rare is the locale lacking in medicinal or culinary hot drinks. With this context, an article title that dampens our enthusiasm for this ritual is eye-catching. The authors of this population-based study in Iran attempted to explore some of the concerns, as cited in their introduction, with regularly exposing our bodies to hot liquids. Other research on this topic has shown a mixture of results, some connections to esophageal cancer, some without an obvious cause-effect (possibly, as the authors hypothesized, due to flaws in data connection, such as recall bias of the study participants regarding their memory of the temperature of the beverages consumed in the past). These uncertainties have led to some ratings of “very hot” (≥ 150° F) beverage drinking as “probably carcinogenic,” rather than the more worrisome “carcinogenic.”
This prospective study was conducted in one province in Iran, a geographic region with a particularly high rate of esophageal squamous cell carcinoma (ESCC), which previous studies had associated with tea drinking. The authors followed 50,045 adults between the ages of 40 and 75 years through home interviews or phone calls. Research staff conducted interviews to identify ESCC risk factors and collected data about demographics and nutrition.
Regarding tea drinking, research assistants asked study participants for a subjective analysis of how warm or hot the tea they drink usually is, as well as the time between tea pouring and drinking. In addition, participants were given tea the temperature of which was measured, and they were asked how the tea they normally drink compares to that tea.
Attempts were made to contact participants annually; fewer than 1% have been lost to follow-up. On average, participants were followed for 10.1 years, during which records indicated that 328 cases of esophageal cancer occurred. Of these 328 cases, 11 were adenocarcinoma by pathology; 317 were presumed to be SCC (285 by pathology, 32 considered “likely” cases). Statistics were run on these ESCC cases in the cohort of 50,027 people, and compared to black tea consumption in mL per day (in quintiles) and tea temperature ranges of < 60° C, 60-64° C, and ≥ 65° C. Green tea consumption was low (average 42 mL daily) compared to black tea (more than 1,100 mL daily). Drinkers were split into two groups based on the quantity consumed.
Then, researchers ran the numbers for tea temperature and tea amount. For drinkers of tea (black plus green) cooler than 60° C, it did not matter how much tea they drank; there was no increased ESCC risk. For drinkers of tea ≥ 60° C, higher amounts showed an increased risk.
In this prospective cohort study that included more than 50,000 people followed over 10 years, Islami et al found that the risk of ESCC was higher for people who drank more beverages that were hot (rather than warm). They pointed to the improvements in their research methodology over past work, namely that an effort was made, through several techniques, to quantify the temperature and amount of the tea consumed in a region of Iran known for both its tea drinking and its incidence of ESCC.
In some respects, the connection between hot beverages and cancer makes sense. The researchers documented the carcinogenic potential that can arise from thermal damage to esophageal tissue or from the formation of carcinogenic compounds. In addition, they described why this might occur only past a certain temperature threshold, perhaps due to damage to the esophageal cells that then permit toxins to lead to DNA damage and oncological change. One class of toxins known to affect people in this area are the polycyclic aromatic hydrocarbons, which enter the human body through diet or cigarette smoking.
Should we counsel our patients to shy away from their favorite tea or coffee? As with other attempts to extrapolate research on one population to other regions or demographics, it is unclear. The most concerning findings here are in those who drank both a lot of tea and at a high temperature (and this was mostly black tea). It probably would be safe to say that if a clinician sees patients who fall into those categories that they would mitigate some of their ESCC risk by moderating both quantity and temperature of the tea consumed. Islami et al did not comment on coffee, nor, for the most part, green tea. The authors’ commentary on the possible involvement of toxins, too, is an interesting bent to these results. It makes one branch out from the temperature and quantity of warm/hot beverages to consider plant quality (e.g., contaminant-free sources) in case the carcinogenic transformation involves toxins, too.