Aims: To investigate the genetic and environmental influences on tea consumption and their commonalities with coffee consumption; and to further examine the genetic and environmental aetiology of preference for tea/coffee.
Design: A classical twin design was used in which the similarity of identical and non-identical twins is compared, enabling estimates of genetic, common environmental and unique environmental influence on the trait.
Setting and participants: An Australian population-based sample of 1796 identical (i.e. monozygotic) and 2013 non-identical (i.e. dizygotic) twin pairs aged 16-87 years was studied, roughly three-fifths of whom were female. The sample represented approximately 70% of those approached for study participation.
Measurements: As part of a Health and Lifestyle Questionnaire, respondents were asked how many cups of each tea and coffee they consumed per day. Additional measures of 'total tea and coffee consumption' and 'preference for coffee' were calculated.
Findings: Age was positively associated with tea consumption but negatively associated with coffee preference; women consumed more beverages than men, but showed a lower preference for coffee. An inverse relation between tea and coffee consumption--larger in females (-0.41) than males (-0.34)--was supported. This association was mediated entirely by the unique environment in males, and by both the unique environment (68.3%) and genes (31.7%) in females. Tea and coffee drinking were shown to have similar heritabilities (0.46) in males, but tea consumption was influenced by common environmental factors whereas coffee consumption was not. Coffee preference was shown to be influenced by genes (0.42) and the unique environment (0.58).
Conclusions: As the patterns of genetic and environmental variation were shown to differ for tea and coffee consumption it may be more informative to retain them as separate measures of caffeine intake in future studies of stimulant use and taste perception.