In the first study to show that the sensations from sampled alcohol vary as a function of genetics, researchers focused on three chemosensory genes — two bitter-taste receptor genes known as TAS2R13 and TAS2R38 and a burn receptor gene, TRPV1. The research was also the first to consider whether variation in the burn receptor gene might influence alcohol sensations, which has not previously been linked to alcohol consumption.
People may differ in the sensations they experience from a food or beverage, and these perceptual differences have a biological basis, explained John Hayes, assistant professor of food science and director of Penn State´s Sensory Evaluation Center. He noted that prior studies have shown that some people experience more bitterness and less sweetness from an alcoholic beverage, such as beer.
"In general, greater bitterness relates to lower liking, and because we generally avoid eating or drinking things we don´t like, lower liking for alcoholic beverages associates with lower intake," he said. "The burn receptor gene TRPV1 has not previously been linked to differences in intake, but we reasoned that this gene might be important as alcohol causes burning sensations in addition to bitterness.
"In our research, we show that when people taste alcohol in the laboratory, the amount of bitterness they experience differs, and these differences are related to which variant of a bitter receptor gene the individual has."
To determine which variant of the receptor genes study participants possess, DNA was collected via saliva samples for genetic analysis. The results appear in the October online issue of Alcoholism Clinical and Experimental Research. Ninety-three people of European ancestry, age 18 to 45, completed all four of the study´s tasting sessions.
People are hard-wired by evolution to like sweetness and dislike bitterness, and this influences the food and beverage choices we make every day, pointed out lead researcher Alissa (Allen) Nolden, a doctoral candidate in food science advised by Hayes. Nolden added that it is also well established that individuals differ in the amount of bitterness they perceive from some foods or beverages, and this variation can be attributed to genetic differences.
Normally, sweet and bitter sensations suppress each other, so in foods and beverages, genetic differences in bitter perception can also influence perceived sweetness.
"Prior work suggests greater bitterness and less sweetness each influence the liking of alcohol beverages, which influences intake," Nolden said. "Here we show that the bitterness of sampled ethanol varies with genetic differences in bitter taste receptor genes, which suggests a likely mechanism to explain previously reported relationships between these gene variants and alcohol intake."
The researchers conceded that the relationship between burn and intake is more complicated, at least for foods, as personality traits also play a role. Some people enjoy the burn of chil peppers, for example.
"Still, anecdote suggests that many individuals find the burn of ethanol aversive," Hayes said. "Accordingly, greater burn would presumably reduce liking and thus intake, although this needs to be confirmed."
Nolden and Haye´s study only used ethanol cut with water, so caution is needed in generalizing how the results apply to alcoholic beverages because in addition to ethanol, almost all contain other sensory-active compounds that may enhance or suppress bitterness. For example, the sugar in flavored malt beverages will presumably reduce or eliminate the bitterness of ethanol while the addition of hops to beer will add bitterness that may be perceived through other receptors.
Hayes suggested that chemosensory variation probably plays little or no role in predicting alcohol intake once an individual is dependent. However, he said that genetic variation in chemosensation may be underappreciated as a risk factor when an individual is initially exposed to alcohol, and is still learning to consume alcohol.
Prior studies by Hayes´ laboratory group and others have repeatedly associated bitter receptor gene variants with alcohol intake, a relationship that was presumably mediated via perceptual differences and thus differential liking. Data from this study begin to fill in the gaps in this chain by showing the sensations evoked by ethanol differ across people as a function of genetic variation.
"Additional work is needed to see if these variants can prospectively predict alcohol use behaviors in naïve individuals," he said. "But biology is not destiny. That is, food choice remains that, a choice. Some individuals may learn to overcome their innate aversions to bitterness and consume excessive amounts of alcohol, while others who do not experience heightened bitterness may still choose not to consume alcohol for many reasons unrelated to taste."