Binge drinking stunts the growth of teenagers’ brains, according to new research.
Experiments on adolescent monkeys found heavy exposure to alcohol reduced the development of both grey and white matter.
Scientists believe the same will apply to humans – and could affect their ability to learn.
Every gram of booze consumed per kilogram of body weight lessened growth of the animals’ neurons by 0.25 millilitres per year.
In human terms that is the equivalent of four beers per day, say the US team.
Lead author Professor Tatiana Shnitko, of the primate research centre at Oregon Health and Science University, said drink abuse is particularly dangerous in adolescence.
She said: “This is the age range when the brain is being fine-tuned to fit adult responsibilities.
“The question is, does alcohol exposure during this age range alter the lifetime learning ability of individuals?”
The UK is among the worst countries for teenage binge drinking – generally defined as downing at least two-to-three glasses of wine or beer in one session.
Girls in England, Scotland and Wales are more prone than boys. Last year they made up three of the top six spots in a World Health Organisation league table of 36 European nations.
The study published in eNeuro found heavy drinking on the ‘cusp of adulthood’ slowed up brain growth in the male and female rhesus monkeys.
It could inform future investigations into how these changes may influence problematic drinking in humans later in life.
Previous research in humans and rodents had already established a link between excessive drinking and reduced brain volume.
Now Prof Shnitko and colleagues – supported by the National Institute on Alcohol Abuse and Alcoholism – have extended these findings.
The first long-term trial of its kind using a non-human primate model showed how voluntary intake of alcohol in late adolescence and early adulthood affects brain development.
Monkeys characterised as heavy drinkers based on their consumption and blood samples suffered dramatic reductions in brain growth.
In particular this was their white matter which helps neurons to communicate and the thalamus – a walnut-sized region of grey matter that relays sensory and motor information.
The researchers examined the brains of 71 rhesus macaques using MRI (magnetic resonance imaging) scans after they voluntarily consumed alcoholic beverages over a period of almost two years.
They precisely measured intake, diet, daily schedules and health care – ruling out other factors that tend to skew results in observational studies involving people.
They wrote: “Chronic alcohol self-intoxication reduced the growth rate of brain, cerebral white matter and sub-cortical thalamus.”
It means alcohol abuse among teenagers and young adults is not only dangerous in its own right – but can actually slow the rate of growth in developing brains, they said.
Most brain growth occurs between the ages of 12 and 17, according to experts. Heavy drinking during this time can make mental illness more likely and cognition more difficult.
The latest findings help validate previous research examining the effect of alcohol use on brain development in people.
Co-author Christopher Kroenke, an associate professor in the Division of Neuroscience at the primate centre, said: “Human studies are based on self-reporting of underage drinkers.
“Our measures pinpoint alcohol drinking with the impaired brain growth.”
Prof Shnitko said previous research has shown the brain has a capacity to recover at least in part following the cessation of alcohol intake.
But it’s not clear whether there would be long-term effects on mental functions as the adolescent and young adult brain ends its growth phase.
Her team plan to explore that in the next stage of their research.
In 2014 a study by Massachusetts University found physical damage to neurons and brain structures caused by binge drinking in adolescence persisted well into adulthood.
It showed changes to the pre-frontal cortex – one of the last brain regions to completely mature – caused lasting harm.
Early onset of drinking, including binge drinking, has been linked to long-term alcohol abuse in adults.
Both the pre-frontal cortex and the cerebral areas of the brain were found to be thinner and have less volume compared to teenagers who did not drink.
These teens also showed less white matter development. These problems could lead to struggles with controlling impulses, remembering events, verbal learning and memory – and making healthy decisions.
Another US study found adolescent brains exposed to periods of binge drinking showed structural and functional abnormalities in the hippocampus – an area of the brain tied to memory and learning.