Growing evidence indicates the role of prenatal hormonal exposure in shaping various personality traits, health predispositions and behaviours. A research team from the Plastic, Reconstructive and Aesthetic Surgery Departmentof the Medical University of Lodz, in collaboration with Professor John Manning from Swansea University (UK), conducted research that provided new data on the links between the ratio of the length of the second to fourth finger and the tendency to engage in risky behaviour, in particular alcohol consumption.

The results, published in the American Journal of Human Biology, indicate an interesting correlation, the more precise understanding of which may help in the analysis of various social and health phenomena. However, as the authors of the publication (https://doi.org/10.1002/ajhb.24187) emphasise, we are talking about correlation, not cause-and-effect relationship.

DIGIT LENGTH RATIO DEPENDS ON PRENATAL EXPOSURE TO SEX HORMONES

The basis of the study was the 2D:4D ratio, i.e. the ratio of the length of the second (index) to the fourth (ring) finger of both hands. Hence the collaboration with Professor John Manning, considered the 'father' of the concept that certain anthropometric measurements, specifically hand measurements, reflect the prenatal hormonal status.

This is also the case with the aforementioned 2D:4D. It is formed in the first trimester of pregnancy under the influence of sex hormones acting on the foetus and remains stable throughout life. For this reason, it can be used as an important diagnostic marker.

'It all results from the fact that in the early prenatal period, in the phalanges of the second and fourth fingers we have different densities of receptors for female hormones, i.e. estrogens, and male hormones, i.e. androgens. There are more of them in the fourth finger, which is why it is more sensitive to changes resulting from the hormonal environment', explains one of the authors of the study, Anna Kasielska-Trojan, PhD, a professor at the Medical University of Lodz and plastic surgery specialist.

'Generally, in men, 2D:4D is lower, i.e. the fourth finger is longer than the second. In women, however, it is higher, reflecting the greater influence of estrogens', she adds.

HORMONAL STORM IN THE MOTHER'S WOMB

Interestingly, the developing foetus is affected not only by hormones produced by its own gonads. 'Of course, the sex of the foetus is of great importance when it comes to exposure to hormones. But there are also a number of environmental factors that affect the mother and consequently also the child's hormonal environment', Kasielska-Trojan explains.

It has been known for a long time that sex hormones determine many very different factors; not only physical ones, but also those related to behaviour, personality traits, predispositions. A higher influence of testosterone is associated with a greater tendency towards aggression and risky behaviour, among other things. 'And the latter also include problematic alcohol consumption', the expert adds.

WHY DO MEN DRINK MORE?

It turns out that differences in the future pattern of alcohol consumption can be encoded already in the prenatal period. Higher levels of testosterone, characteristic of male foetuses, increase tolerance to alcohol. In addition, men's stomachs contain enzymes that reduce its absorption by about 30 percent compared to women. As a result, women absorb more of it into the bloodstream; it affects them faster and more strongly. Both of these factors influence the formation of drinking habits and differences in alcohol-related behaviour between the sexes.

A LONGER RING FINGER - A GREATER PRONENCY TO RISK

Unlike previous studies that focused on populations of people addicted to alcohol, the team from Łódź conducted an analysis on a randomly selected group of students: a total of 258 people, 169 of whom were women. The study participants were subjected to the AUDIT (Alcohol Use Disorders Identification Test), which is a commonly used tool to assess problematic (risky) alcohol consumption, including determining the likelihood of addiction. Additionally, all respondents reported the amount of alcohol they consumed in standard units.

As the results showed, a lower 2D:4D index, especially in the male group, negatively correlated with higher results obtained in the AUDIT test, which may indicate a higher risk of problematic alcohol drinking. In women, this correlation was also present, although slightly weaker.

Kasielska-Trojan emphasises that the results indicate only a correlation, not a cause-and-effect relationship. Prenatal exposure to sex hormones reflected by a lower 2D:4D index may be one of many factors influencing risky behaviours, including alcohol consumption. 'However, the results we obtained suggest that the lower this index, i.e. the higher the exposure to androgens in the prenatal period, the greater the predisposition to obtaining high scores in the AUDIT test', she explains.

Thus, the Łódź study joined the growing pool of publications indicating the importance of prenatal influences in shaping future behaviours and health. Understanding these relationships can help identify risk groups and design preventive measures.

BROADER APPLICATION OF THE 2D:4D RATIO

Anna Kasielska-Trojan reminds that 2D:4D is used in many fields of science. In addition to research on alcohol consumption, it has been analysed in the context of conditions such as idiopathic gynaecomastia (enlargement of the mammary glands in men), breast, prostate and lung cancers, autoimmune diseases, e.g. lupus or thyroid disease.

It has also been studied in the context of neurological disorders such as autism, ADHD and Alzheimer's disease, and even the severity of COVID-19, and oxygen consumption in athletes. That is, wherever there are gender differences in the frequency of occurrence of given phenomena.

Although 2D:4D is currently a tool used mainly in scientific research, its potential in clinical practice is also promising. Scientists would like it to be used as a diagnostic marker for conditions related to hormonal disorders, or as a risk indicator in the prevention of certain diseases.

In the social context, the discussed study emphasizes how important it is to understand that some predispositions to behaviours and diseases may have their origins in the prenatal period. Its authors emphasise that alcohol abuse is a serious social and economic problem, and a better understanding of the biological mechanisms behind this phenomenon can help develop more effective prevention and intervention strategies.

The results of the research by the team led by Anna Kasielska-Trojan and Bogusław Antoszewski have attracted the attention of many foreign media. Reports about their research appeared in the New York Post (USA), Today Headline (USA), Science Daily (USA), Mirage News (Australia), WDC.TV (Canada), ET Today (Taiwan), PC Home (Taiwan) and GB News (UK).

PAP - Science in Poland, Katarzyna Czechowicz

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