A team of scientists have been investigating why people continue to drink tea, coffee and alcohol despite their bitter taste. They wanted to understand the biological aspect of taste. The drinks are often the subject of studies which conclude that they are beneficial or harmful to people’s health, but don’t often refer to the taste. Taste tests can be expensive to conduct, but recent advances could help this study. The study was published in Scientific Reports on an open access basis, by scientists from Northwestern University and QIMR Berghofer Medical Research Institute in Australia.
The scientists used the UK Biobank, a charitable international health resource, which recruited 500,000 people in 2006-2010, aged between 40-69 years. The participants provide samples, including urine, blood and saliva for future analysis, offered detailed personal health information and agreed to follow-ups on their health. The resource aims to improve the prevention, diagnosis and treatment of serious and life-threatening illnesses. Data can be made available to approved scientists who are conducting a scientific study to benefit public health. Findings should be returned to the UK Biobank when the study is finished. There is no upper age-limit for participants, and the aim is to follow their health for many years.
Sensitivity to a bitter taste is caused by a genetic variant, but scientists were surprised to find that the more sensitive to the bitter taste of caffeine that people were, the more coffee they drank. The results seemed to suggest that people were able to acquire a taste for coffee, via learned reinforcement which offered a positive experience through the coffee drinking. People who preferred the taste of coffee, drank less tea. Certain genetic sensitivities affected which drink people preferred. People who were sensitive to quinine and PROP, a synthetic taste related to compound found in cruciferous vegetables, were less likely to enjoy the taste of coffee. People who were sensitive only to PROP drank very little alcohol, especially red wine.
The scientists used Mendelian randomisation (MR), often used in epidemiology, to find the cause of the relationship between the type of drink consumed and the bitter taste of that drink. Genetic variants related to quinine, PROP and caffeine had been studied through analysing solution taste ratings which had been found during a study involving Australian twins.
Participants were asked to answer questionnaires, based on which drink they preferred and the number of cups of tea and coffee they consumed daily. Decaffeinated drinks were included. Participants were also asked about the number of times they drank alcohol in a week. All participants in the UK biobank had been genotyped and were all of white British ancestry. The scientists set definitions to determine between heavy and light drinkers of the different beverages. They also investigated differences in gender, but found little to support it apart from the association between caffeine perception and tea intake which seemed to be much stronger for women.
Strengths of the study included avoiding biased estimates by using a two-sample approach in MR and using a mixed model approach to gain higher statistical power. Although the scientists used an arbitrary choice of cut-off to distinguish between high coffee and tea drinkers, they found that moving the cut-off point made no real difference to the results.
Limitations included the study used to estimate the SNP-bitter taste associations was only based on around 1750 people, which is a small sample. The population in the UK biobank may not reflect the population as a whole, and the study included self-reporting which can be unreliable. Black and green tea were the teas used, and other teas may not produce the same results, nor may a non-European population. Health outcomes could be affected, given the amount of tea, coffee and alcohol drunk, but the scientists recommended that this be investigated by other studies.
Ong, J-S., et al., Understanding the role of bitter taste perception in coffee, tea and alcohol consumption through Mendelian randomisation, November 2018, Scientific Reports, Article no: 16414