Coffee drinking habits shaped more by environment than genetics, study of 553 twin pairs finds

Does genetics influence whether a person drinks coffee? A new study by Korean researchers analyzing twins found that while genetic factors play some role in individual differences in coffee-drinking behavior, environmental factors unique to each person have a greater impact.

According to the Korea Food Communication Forum (KOFRUM) on Wednesday, a joint research team — including Lee Jeong-eun, a professor in the Department of Food and Nutrition at Seoul National University, researcher Cho Min-su, and Yoon Ji-young, a professor in the Department of Food and Nutrition at Chung-Ang University — analyzed the relative contributions of genetic and environmental factors to coffee, tea and caffeine consumption among Korean twins. Lee served as the corresponding author of the study.

The researchers chose twins as their subjects specifically to separate and estimate the influence of genetic versus environmental factors. Identical twins share virtually 100 percent of their genetic information, while fraternal twins share on average about 50 percent — similar to ordinary siblings. If identical twins show more similar coffee-drinking behavior than fraternal twins, that difference can be used to statistically estimate the contribution of genetic factors.

This "twin study" method is a standard approach in behavioral genetics for analyzing how much genetics and environment each contribute to individual differences in a given behavior or trait. The heritability figure produced by twin studies, however, does not indicate how much genes affect a specific individual. Rather, it reflects how much of the observed variation among individuals in a given study population can be attributed to genetic differences.

The research team analyzed data from 1,106 twins aged 30 and older who participated in the "Healthy Twin Study," part of the Korean Genome and Epidemiology Study. The sample comprised 553 pairs in total — 456 identical twin pairs and 97 fraternal twin pairs — with a mean age of about 38.6. Approximately 88 percent of participants currently drank coffee, and about 78 percent drank tea. Average daily caffeine intake was about 64.9 milligrams.

When the team compared how similarly identical and fraternal twins behaved in terms of coffee drinking to assess genetic and environmental influences, they found that genetic factors explained 29 percent of the individual variation in whether a person drinks coffee — a figure known as heritability. The remaining 71 percent was attributed to unique environmental factors, which include both individual-specific environmental influences and measurement error. This does not mean that 29 percent of any one person's coffee-drinking behavior is determined by their genes, nor that a parent's coffee habits are passed on to children with a 29 percent probability. It means that about 29 percent of the observed differences in coffee-drinking behavior within the study population can be explained by genetic differences.

For tea drinking, the genetic contribution was even lower. Heritability for whether a person drinks tea stood at 11 percent, with unique environmental factors accounting for 89 percent. The caffeine intake analysis drew on complete dietary data from 319 twin pairs, or 638 individuals. When the team divided participants into high- and low-intake groups using the median daily caffeine intake of 55.55 milligrams as the cutoff, heritability was 27 percent and the influence of unique environmental factors was 73 percent. When caffeine intake was analyzed as a continuous variable, the heritability estimate was 17 percent.

The findings show that while genetic background plays some role in coffee and caffeine consumption, genetics alone cannot fully explain coffee-drinking behavior. For coffee consumption in particular, individual environmental factors carried more weight than genetic ones.

Physiological responses to caffeine and the speed at which it is metabolized can vary from person to person. Caffeine works by blocking adenosine receptors in the brain, reducing drowsiness and increasing alertness. Genetic differences involved in caffeine metabolism and response may also be linked to how individuals react to caffeine.

The study is also notable because previous twin research on caffeine consumption has focused primarily on Western populations. The researchers said that, to their knowledge, this is the first study to examine the heritability of coffee drinking and overall caffeine intake in an East Asian population.

Caution is warranted against reading the results too simply as "29 percent genetics versus 71 percent lifestyle," since the portion classified as unique environmental factors may include not only individual living environments but also measurement error.

The study also did not examine whether drinking coffee prevents specific diseases or improves health outcomes. Its core contribution lies in analyzing how much genetic and environmental factors each contribute to individual differences in coffee, tea and caffeine consumption observed in a Korean twin population. Coffee contains not only caffeine but also a range of bioactive compounds, including chlorogenic acid, and research on the relationship between moderate coffee consumption and health continues to accumulate.

The study — titled "Genetic and Environmental Influences on Caffeine Intake in Korean Twins" — was recently published online in the international academic journal Behavior Genetics.