Results from this case-control study do not support the hypothesis that tea consumption is inversely associated with risk of SCC. There was no effect of dose, duration, or combined dose-duration variables for tea consumption on risk of SCC.
Previously published case-control studies of tea consumption and SCC risk have yielded mixed results.1–3
A case-control study drawing on subjects from the Southeastern Arizona Health Study, (n=450) reported that while there was no association between any tea consumption and SCC risk, there was a protective effect for hot black tea after adjusting for brewing time (OR=0.33, 95% CI 0.12–0.87).1
Antioxidant activity as well as the content of the polyphenols in tea has been shown to increase with the brewing time.6
A follow-up study using the same source population2
reported that compared to non-tea drinkers, hot tea drinkers had a lower
, but statistically non-significant risk of cutaneous SCC (adjusted OR = 0.63, 95% CI 0.36–1.10) whereas iced tea drinkers were at a slightly higher
, non-statistically significant risk (OR = 1.02, 95% CI 0.64–1.63). Finally, a population based case-control study of 696 individuals with primary invasive SCC and 715 age- and sex-matched controls showed that ever having regularly consumed tea (≥ 1 cup/day for ≥ 1 month) was associated with a significantly lower risk of SCC (OR = 0.70, 95% CI 0.53–0.92).3
There was further risk reduction with increased duration and dose of tea consumption.
These conflicting findings may be explained, in part, by differences in the source populations, including differences in mean age (younger mean age in other published studies compared to our study), skin type (skin with tendency to burn: 23% of participants in our study vs. 25%1–2
in previously published studies), tea consumption patterns (iced tea consumption was more prominent in the Arizona population), and sun exposure history (due to geographic variability). The photoprotective effects of tea may be modified by skin type such that effects are more pronounced in source populations that consist of people with lighter complexions.
Strengths of this study include a large sample size (n=830), thorough measurement of exposure including overall use, dose, and duration and adjustment for SCC risk factors such a skin type and sun exposure history, which could potentially modify the effects. There are several potential limitations to this study, including the possibility of recall bias, selection bias, and limitations of generalizability. Differential misclassification would result if the cancer diagnosis served as a stimulus for cases to recall tea consumption exposures more or less thoroughly than controls, but this is not likely given that the cutaneous chemopreventive effects of tea consumption are not widely recognized, and tea drinking was only one of several different exposures ascertained in questionnaire. The generalizability of our study may be limited because we only studied KPNC members, although previous studies have shown that the KPNC membership is highly representative of the surrounding region except for the tail ends of the income distribution.7–8
Finally, we did not collect information on tea consumption patterns such as hot versus cold tea consumption, green versus black tea, or brewing time, which may impact antioxidant potency.
In this case-control study, we did not detect any consistent relationships between tea consumption and SCC risk. Amount and duration of tea consumption did not appear to alter risk of SCC. Given the differences in conclusions depending on the population studied, further studies may be warranted.