Javier Hirschfeld/BBC/Getty Images via BBC

Alcohol is a toxin. Its dangers span fatal accidents, liver disease, and many kinds of cancer. Even small quantities can be carcinogenic, leading the World Health Organization to declare that “when it comes to alcohol consumption, there is no safe amount that does not affect health”.

Although beer and wine are commonly seen as safer drinks, as the US guidance states, the type of drink is not the important factor – instead, it’s the amount of alcohol consumed: “One 12-ounce beer has about the same amount of alcohol as one 5-ounce glass of wine or 1.5-ounce shot of liquor.”

There are numerous reasons why alcohol may be more dangerous for younger people. One is body size and shape: teenagers don’t reach their adult height until 21, and even after they have stopped growing vertically, they may lack the bulk of someone in their 30s or 40s.

“Drinking one glass of alcohol therefore results in a higher blood alcohol content for young people than for adults,” says Ruud Roodbeen, a post-doctoral researcher at Maastricht University and the author of Beyond Legislation, which examines the impact of raising the minimum drinking age.

When you drink alcohol, it enters your bloodstream and spreads through your body. Within 5 minutes, it reaches your brain, easily crossing the blood-brain-barrier that generally protects your brain from harmful substances. “A relatively large part of the alcohol ends up in the brains of young people, and that is yet another reason why young people are more likely to get alcohol poisoning,” says Roodbeen.

Shaping the brain

Equally important are the changes occurring within the skull. In the past, neural development was thought to stop in our early teens, but a swathe of recent research shows that the adolescent brain undergoes a complex rewiring that does not end until at least the age of 25.

The most important changes include a decline in “grey matter” as the brain prunes away the synapses that allow one cell to communicate with another. At the same time, white matter – long-distance connections known as axons covered with an insulating fatty sheath – tends to proliferate. “They are like the brain’s super-highways,” says Lindsay Squeglia, a neuropsychologist at the Medical University of South Carolina. The result is a more efficient neural network that can process information more quickly.

The limbic system, involved with pleasure and reward, is the first to mature. “These areas are fully adult-like during adolescence,” Squeglia explains. The prefrontal cortex, which is located behind the forehead, is slower to ripen. This region is responsible for higher-order thinking – which includes emotional regulation, decision-making, and self-control.

The relative imbalance of these two regions’ development can explain why adolescents and young adults tend to be more risk-taking than adults. “A lot of people describe the adolescent brain as having a fully developed gas pedal without brakes,” says Squeglia. And bathing our neurons in alcohol – which is known to release inhibition – may only amplify this thrill chasing. For particularly impetuous teenagers, alcohol can create a vicious cycle of bad behaviour and delinquency. “The more impulsive kids tend to drink more, and then drinking causes more impulsivity,” says Squeglia.

At high enough frequencies and volumes, adolescent drinking could impair the brain’s long-term development. Longitudinal studies show that early drinking is associated with a more rapid decline in grey matter, while the growth of the white matter is stunted. “Those super-highways aren’t getting paved as much in kids who start drinking,” says Squeglia.

The consequences may not be immediately evident in cognitive tests; in a young brain, the regions responsible for problem solving can work a little bit harder to make up for the deficits. It cannot keep this up forever, however. “After multiple years of drinking, we see less activation in the brain and poorer performance on these tests,” says Squeglia.

Early drinking can also take its toll on mental health, and heightens the risk of alcohol abuse later in life. This is particularly true for people who have a family history of alcoholism – the earlier they start, the greater their chances of developing a drinking problem themselves. The genes associated with an advanced risk of alcohol abuse seem to be most influential during this critical period of brain development. “And the longer that someone is able to wait, the less likely these genes are going to come into play,” says Squeglia.

Squeglia says that, in her public talks on alcohol consumption, members of the audience often raise the question of the “European model of drinking”. In some countries such as France, minors are allowed to have a glass of wine or beer to accompany a family meal. Even outside of Europe many parents believe that slow introduction to alcohol in a controlled context teaches young people to drink safely and reduce binge-drinking later on, whereas restriction leads it to become a tempting “forbidden fruit”.

This is a myth. “The research has shown that the more permissive a parent is with alcohol use, the more likely a kid is to have problems with alcohol later in life,” says Squeglia. A comprehensive review suggests that contrary to the forbidden-fruit belief, “parents imposing strict rules related to adolescent alcohol use is overwhelmingly associated with less drinking and fewer alcohol-related risky behaviours”.

Nor does the idea of a healthy European drinking culture hold true over a lifetime. According to the World Health Organization, data indicates that half of all alcohol-attributable cancers in the European region are caused by light and moderate alcohol consumption.

James MacKillop, who studies addictive behaviour at McMaster University in Hamilton, Ontario suggests adolescents could be provided with better education about alcohol’s risks, and the ways that it can affect the maturing brain.

~ edited excerpts from “Why alcohol is so dangerous for young adults’ brains” by David Robson, BBC (1 March 2024)