The Risks Of Drinkers: A Twin Study Investigating The Role Of Genes And Environment In Alcohol Abuse

Scientists have investigated whether education changes the risk of adolescents that drink a dangerous amount. The answer is no, but education influences other risk factors.

Nearly 3.3 million people worldwide die every year as a consequence of alcohol abuse. For young men, alcohol is among the most frequent causes of death. What is it that makes people consume alcohol in dangerous amounts, even at a younger age?

It is well established that social/economic status carries an enormous influence on health. The association is often so strong that scientists believe it to be a major contributor to onset diseases. People with low social status not only suffer more often from diabetes, depression, and obesity, they also estimate their own health as worse than others. On the other hand, education is important for peoples’ status, because it often results in better jobs, higher income, and a better social environment. But does education also determine drinking behavior? And if so, why is that the case? Does education modify the influence of genes and the environment? Both factors are known to affect whether someone drinks too much alcohol.

Scientists, under Peter Barr from the Virginia Commonwealth University, speculate that education manipulates the influence of genes and the environment to the same degree. Higher education — according to their hypothesis — would demonstrate a higher relevance of genes, while at a lower educational level, the influence of the environment would dominate. They tested their hypothesis in a  study (1).

Finland seems to answer this question specifically well. Alcohol consumption is quite popular in this northern country. And despite the fact the alcohol is permitted by law at only the age of 18, about one-third of adolescents acknowledge they drank before age 13. Scientists concentrated on twins, as they specifically allow to distinguish the influence of genes and environment. A characteristic that is completely inherited would always occur (statistically speaking) in monozygotic (identical) twins in both siblings, while only in half of the cases in dizygotic (non-identical) twin pairs. As they (usually) grow up together, environmental influences  should affect both monozygotic and dizygotic twins to the same degree.

The data for this study came from the Finnish population registry. Scientists questioned about 5,600 twins. They wanted to know how often they drink alcohol and how often they are drunk. Twins also selected the category that described their educational degree best. These questions were answered at age 12, then again at age 14, 17.5, and again sometime between ages of 20 and 26. However, not all twins continued to contribute to the very end; the last question was completed by only 3,400 of them. Then, the data was evaluated.

“We could see that lower education was associated with a larger number of intoxication events,” says Peter Barr, first author of the paper. A higher education was instead associated with a higher drinking frequency. Both effects were very small, however. Scientists were surprised by another finding: education exhibited  no influence of the genetic risk factors, but on the environmental influences; the lower the educational level, the higher the effect of these risk factors. With increasing educational level, the influence of genes became more visible, especially in males.

However, it was not because the genetic influence increased that it remained stable across all educational levels, as Barr explains. But the environmental factors that determine how often and how much a young person drinks decreased in their relevance. At a very high educational level, they seem to play no role at all. Taken together, education seems to exhibit only a minor influence on regular and risky drinking behavior in adolescents. Other factors appear to play a larger role, such as the individual life history. The more bad experiences a young persons has had, the more likely he/she approaches alcohol.

Whether these results hold true for other countries with larger social heterogeneity and in other phases of life will need to be investigated in future studies.

This is part 6 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon.

Reference:

1. Barr PB, Salvatore JE, Maes H, Aliev F, Latvala A, Viken R, Rose RJ, Kaprio J, Dick DM. Education and alcohol use: A study of gene-environment interaction in young adulthood. Soc Sci Med. 2016 Jun 22;162:158-167.