Teens who drink heavily are more likely than their peers to have less gray matter, an important brain structure that aids in memory, decisions, and self-control, according to a Finnish study.

The study was observational, so it is impossible to say whether heavy drinking caused this stunted brain development. People may have less brain matter due to genetic factors, and this abnormality may make them more likely to abuse alcohol, the researchers write in the journal Addiction.

"Substance use has been found to be connected to social exclusion, mental health problems and lower educational attainment," said lead author Noora Heikkinen of the University of Eastern Finland.

Having less gray matter may cause similar problems, as gray matter contains most of the brain's neurons and plays an important role in memory, emotions, decision-making, and self-control.

"Brain structural changes might be one factor that contributes to the social and mental problems among substance-using individuals," Heikkinen told Reuters Health by email.

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To explore the effect of alcohol use on developing teenage brains, the researchers studied 62 young adults who were participating in the Finnish Youth Wellbeing Study.

Between 2013 and 2015, the participants filled out questionnaires, answering questions about how often they drank and how many drinks they consumed.

The participants had all completed similar questionnaires five and 10 years earlier, starting at age 13.

As teens, 35 of the participants fell into the category of heavy drinkers. For example, they drank four or more times a week, or they drank less often but when they did, they drank heavily. The other 27 young adults in the study were considered light drinkers.

No one in either group showed symptoms of depression or other serious mental illnesses. Heavy and light drinkers had similar rates of anxiety, personality disorders, and drug use. Heavy drinkers were significantly more likely to smoke cigarettes than light drinkers, however.

But when participants underwent brain scans to look at gray matter and other brain structures that may be affected by alcohol use, the heavy drinkers had smaller volumes of gray matter in several brain areas when compared with the light drinking group.

Specifically, those areas are known as the bilateral anterior cingulate cortex, the right orbitofrontal and frontopolar cortex, the right superior temporal gyrus and the right insular cortex.

The frontal section of the brain, which helps people plan and make decisions, continues developing until people reach their early 20s, said Samantha Brooks, a lecturer at the University of Cape Town in South Africa who studies the effects of drinking on adolescents.

During this period of brain development, teens are in a "vulnerability window" where they may be more likely to develop substance use problems, said Brooks, who was not involved in the study.

In addition, if teens drink heavily during this sensitive time, they may cause damage to their brains that can make their drinking behavior worse and cause other problem behaviors like missing school or having unsafe sex, Brooks said.

"Parents and teachers must be alert to the vulnerability window during adolescence, and seek help as early as possible, to prevent more serious damage to the brain," Brooks said by email.

Stopping alcohol use can increase gray matter volume when it is done early enough, Heikkinen noted. "However, when alcohol use has continued for a long time, some structural changes become irreversible," Heikkinen warned.

"Teenage years are very important for brain development, and alcohol can tamper with this process," Heikkinen said.