Researchers at the University of Southern California looked at more than 17,000 brain scans to see if daily smoking and drinking advanced brain age.

The study found that every gram of alcohol consumed a day aged the brain by 11 days. Smoking a pack of cigarettes a day for a year aged the brain by 11 days.

It is one of the largest studies ever done on brain aging and alcohol, making the findings quite robust.

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Over time, drinking a little bit more alcohol than recommended could accelerate the brain's aging process, according to a new study.

Though previous studies have found the same, most were tentative findings based on small groups of people or large groups of mice.

The new study, from researchers at the University of Southern California, offers a more robust estimate, reached by examining 17,308 human brain scans from the UK Biobank — one of the biggest sample sizes ever seen.

The team found that for every gram of alcohol consumed a day, the brain aged 0.02 years — or, seven-and-a-half days. (The average can of beer or small glass of wine contains 14 grams of alcohol). People who reported drinking every day had brains which were, on average, 0.4 years older than people who didn't drink daily.

Smoking had even stronger effect: the team found that those who smoke a pack of cigarettes a day for a year age their brains by 0.03 years (11 days).

This was one of the biggest studies ever, so scientists taught a computer to work out each person's 'brain age'

The researchers took 30% of the brain scans in their study, all from people aged 45 to 81, and used them to train a computer, which scanned each brain to see how old or young they looked.

They then compared the computer's estimates of each brain's age with the person's real age, and their self-reports of how much alcohol and tobacco they consume daily, in order to see if consuming alcohol or tobacco regularly aged the brain.

Comparing those results with the other 70% of their brain scans, they found that the more you drank and smoke, the more likely you were to have a brain aged beyond your actual age.

Lucina Uddin, director of the Cognitive and Behavioral Neuroscience Division at the University of Miami, who was not involved in the study, told Insider that the use of an algorithm is what makes this study's findings so compelling.

"Back in the day we'd scan 20 or 40 subjects, if we were lucky, for neuroimaging studies," Uddin said. "Now we're getting bigger numbers like 200 or 300 individuals. But this is the biggest sample we've ever seen."

Daily drinking does have a real impact on the brain, experts say, but the occasional drink can be good for the heart

Because the sample size is so big, scientists can ask questions that apply to the entire population, rather than just a few people.

Brain age is essentially a measure of brain health, says Uddin, who was not surprised by the study's findings.

"Looking at brain age is a way of checking how well you've been taking care of your brain," she told Insider. "My age is 40, but does my brain look more like a 50-year-old brain or a 60-year-old brain? Do you look younger than your age or older than your age?"

The lead author of the study, Arthur Toga, told Inverse: "The 0.4 years of difference was statistically significant. We suggest that daily or almost daily alcohol consumption can be detrimental to the brain."

However, many super-agers — people who live well beyond 100 years old, and often appear resistant to the dementia gene — report drinking alcohol now and then.

What's more, a recent Harvard study found drinking in moderation can have some benefits, particularly for the heart.

Dr. Qi Sun, a co-author of the Harvard study, previously told Insider: "If you drink alcohol, it's very important that you drink responsibly, not in excess, and that you also focus on eating a healthy diet, maintaining a healthy body weight, not smoking, and exercising. If you don't drink you don't need to start drinking."

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