Tea drinking habits and oesophageal cancer in a high risk area in northern Iran: population based case-control study

In a recently published paper in the "British Medical Journal", a joint collaboration of well-known international scientists represented by Islami et al. has tackled this issue.1 In a well-designed, laborious case-control study in Golestan, Iran, they looked at 300 cases of esophageal SCC and 571 age and sex matched neighborhood controls, assessed the temperature of the commonly used drink "tea" among them and compared it between the two groups. After adjusting for several confounders including ethnicity, daily vegetable intake, alcohol consumption, tobacco or opium use, duration of residence in rural areas, education level and car ownership (the latter two as indices of socio-economic status), they found that consuming hot tea is associated with significantly increased chance of developing esophageal SCC. The adjusted odds ratio(OR) for developing esophageal SCC in those who reported drinking "very hot tea" was 8.16 (95% CI: 3.93 to 16.91) as compared to those taking warm or lukewarm tea (P<0.001) and for those drinking "hot" tea the adjusted OR was 2.07 (95% CI: 1.28 to 3.35). According to Islami et al., 21.1% and 36.2% of the cases drank their tea "very hot" or "hot", respectively. Self-claim of "hot", "very hot", and "warm or "lukewarm" tea drinking correlated with the claimed time from pouring tea to its drinking by the individual (weighted kappa statistics: 0.69). They did not find any correlation between amount of tea consumed and development of esophageal SCC. They have also reported limited data of tea temperature measurement in addition to the self claims of tea drinking habits (as mentioned for the case-control study) from a large on-going cohort study in the same region. The authors conclude that it is probably the "hotness" rather than the "tea" which is responsible for this increased chance of SCC of esophagus. In an accompanying editorial, Whiteman suggests that people drink their tea at least 5 minutes after pouring it in their cups.