Prenatal hormone exposure may shape alcohol drinking habits, new research suggests

A new study published in the American Journal of Human Biology suggests that the length of your fingers—specifically the ratio between your index and ring fingers—might predict how much alcohol you consume. Researchers found that students with longer ring fingers compared to index fingers tended to drink more, especially men. These finger ratios are thought to reflect hormone levels in the womb, meaning the roots of drinking behavior could be influenced before birth.

The research team, made up of scientists from Swansea University and the Medical University of Lodz, wanted to explore whether prenatal hormone exposure might shape future behaviors, like alcohol use, in people who are not alcohol dependent. Earlier studies had shown a link between the so-called “digit ratio” and alcohol problems in clinical populations, but the strength of this association in everyday drinkers was less clear. The current study aimed to fill this gap by measuring finger lengths directly and comparing them to alcohol use in a large sample of university students.

To test their ideas, the researchers recruited 258 students from the Medical University of Lodz in Poland. The sample included 169 women and 89 men, with an average age of about 22. Researchers measured each participant’s height, weight, and finger lengths on both hands. Specifically, they calculated the ratio between the second digit (index finger) and the fourth digit (ring finger), known as the 2D:4D ratio. Lower ratios mean the ring finger is longer than the index finger. This ratio is believed to reflect how much testosterone and estrogen a person was exposed to during early pregnancy.

To assess alcohol use, participants completed the Polish version of the Alcohol Use Disorders Identification Test, a ten-item questionnaire developed by the World Health Organization. This tool provides a score from 0 to 40, with higher scores indicating greater risk for harmful drinking. It also allowed the researchers to estimate how many grams of alcohol each person consumed weekly. Participants filled out the form anonymously after their finger lengths were recorded, and their results were grouped into categories based on risk level, from abstinent to possibly addicted.

The researchers found that students with lower digit ratios, particularly on the right hand, reported drinking more alcohol. This relationship was especially strong in men. For example, men with lower right-hand 2D:4D ratios had higher alcohol use scores and consumed more alcohol weekly. These associations were moderate to large in strength. Among women, the associations were smaller but still present. Notably, the left-hand finger ratios did not show any connection to alcohol use.

When the researchers looked more closely at body size, they found that men who were taller and heavier also tended to drink more. However, these physical traits did not explain the link between digit ratios and alcohol consumption. Even after accounting for height, weight, and finger length, the finger ratio remained a significant predictor of how much alcohol someone drank. In contrast, body size measures were no longer associated with alcohol use once digit ratio was taken into account.

The results support the idea that prenatal hormone exposure may play a role in shaping alcohol-related behaviors later in life. A lower 2D:4D ratio is thought to indicate higher exposure to testosterone and lower exposure to estrogen before birth. These hormone levels are believed to influence brain development, including traits related to risk-taking and reward sensitivity. Because alcohol use, especially at high levels, often overlaps with risk-taking tendencies, the researchers suggest that early hormone exposure might increase the likelihood of heavier drinking through this pathway.

Interestingly, the association between digit ratio and alcohol consumption was strongest in the right hand and in men, a pattern that has been seen in other studies. This may reflect sex-specific effects of hormones during fetal development, as men typically have lower 2D:4D ratios than women. The study also reinforces the idea that right-hand measurements are more sensitive to prenatal hormone effects than left-hand ones.

The study does have some limitations. One issue is the imbalance between male and female participants, with nearly twice as many women in the sample. This is common in medical universities in Poland, where the study took place, but it may have influenced the results. Also, while the study focused on alcohol consumption, it did not collect data on other behaviors—such as impulsivity or sensation-seeking—that might help explain why digit ratio and drinking are related.

Another factor not accounted for in the study is genetics. Some genetic variations are known to affect alcohol metabolism and the risk of alcohol dependence. While the study highlights the role of prenatal hormone exposure, it does not explore how this may interact with genetic risk factors. Moreover, alcohol use is influenced by many environmental and social factors that were not part of the analysis.

The researchers also note that behaviors associated with risk-taking peak during adolescence and young adulthood—exactly the age group studied here. Since lower digit ratios are linked to greater risk-taking tendencies, it is possible that the finger length-alcohol use connection reflects a broader personality profile. Future studies could examine whether digit ratios predict not only drinking but also other behaviors, such as gambling, drug use, or reckless driving.

Despite these limitations, the findings add to a growing body of evidence that the roots of certain behaviors may be traced back to biological factors shaped before birth. While finger length alone cannot determine a person’s habits, it may serve as one of many clues about predispositions that interact with life experiences. The researchers hope that further work can clarify how prenatal conditions influence adult behavior and whether this knowledge can help in preventing harmful patterns of alcohol use.

The study, “Is Alcohol Consumption Pattern Dependent on Prenatal Sex-Steroids? A Digit Ratio (2D:4D) Study Among University Students,” was authored by Barbara Ślawski, Anna Kasielska-Trojan, John T. Manning, and Bogusław Antoszewski.