Caffeinated beverages liking varies by demographic, social, and environmental factors (Brice and Smith 2002). However, studies provide powerful evidence for a genetic determination of beverages consumption. Previous twin studies on caffeine intake reported heritability estimates for tea and coffee consumption ranging from 0.26 to 0.36 and from 0.41 to 0.51, respectively (Luciano et al. 2005; Teucher et al. 2007). Coffee and tea intakes were considered as caffeine-related traits. So, lower heritability for tea drinking was attributed to its lower caffeine content (Yang et al. 2010). Genome-wide association studies (GWAS) on habitual caffeine consumption have mainly targeted coffee intake, as coffee widely contains more caffeine than tea. Studies were conducted by the only monitoring of coffee average daily consumption (Sulem et al. 2011; Amin et al. 2012; Cornelis et al. 2015; Cornelis et al. 2016; Pirastu et al. 2016; Nakagawa-Senda et al. 2018) or using calculation algorithms assuming the content of caffeine in different caffeine-containing foods and beverages where a tea cup caffeine amount was estimated as the one third (Cornelis et al. 2011) or the half (Rodenburg et al. 2012; McMahon et al. 2014) of that contained in a coffee cup. Thus, few studies reported the genetic association with habitual tea intake.
On the other hand, the way caffeinated beverages are made and consumed may vary widely, as through extensive areas in North Africa where green tea decoction is a very popular beverage. This tea, prepared by the cooking of the dried tea leaves in boiling water, is characterized by its higher content of polyphenols and caffeine (almost the double of green tea infusion content) (Snoussi et al. 2014).