According to an analysis of brain images taken from 11,651 participants in the UK Biobank, a national health register in the United Kingdom, every gram of alcohol consumed per day was linked to 0.02 years of brain aging — that's about a week of additional aging in the brain.

Cumulatively, people who reported drinking every day or on most days, had about 5 months (0.4 years) of additional aging in their brains compared to people who were the same chronological age as them, but reported less frequent drinking, the study finds. That suggests that their frequent drinking habit aged their brains at an accelerated rate.

Every gram of alcohol consumed per day linked to a week of additional aging in the brain. 

The good news is that these changes are relatively modest. Arthur Toga, the study's senior author and professor at University of Southern California, says that it's unclear how these changes in the brain actually affect people's quality of life. But the bad news is that they're still significant.

"The 0.4 years of difference was statistically significant. We suggest that daily or almost daily alcohol consumption can be detrimental to the brain," Toga says.

The paper was published Thursday in the journal Scientific Reports.

What speeds up brain aging? 

The researchers estimate Relative Brain Age using MRI scans gathered from 5,193 participants. The metric offers a way to compare brain aging amongst people who are all the same chronological age, and illuminate how outside influences can lead someone's brain to age at a different rate relative to their peers.

The scans record decreases in the brains white matter (densely connected nerve fibers that help usher electrical signals through the brain) grey matter (another type of brain tissue that wastes away as cognitive function declines) and other metrics related to brain volume associated with brain aging.

How fast a person's brain ages depends on both genetics and the environment — and that includes our habits. In the study, the team zeroed in on smoking and drinking habits among 11,651 participants.

When it came to booze, the biggest effects on brain aging were seen in those who drank the most alcohol – people who reported drinking every day or on "most days". People who drank that much had brains about five months older on average than people of the same biological age who drank less frequently.

Cigarette smoking may have an even more dramatic aging effect, the study suggests. Each year spent smoking one pack of cigarettes per day led to about about 11 additional days (0.03 years) of brain aging, the team calculated. Over time, that meant that those who smoked most often — usually every day — had brains between 6-7 months older on average than those who smoked less frequently or not at all.

Giuseppe Barisano, a post-doctoral research fellow at USC tells Inverse that these differences in brain age may be clinically relevant for heavy drinkers or smokers in the future. Barisano has worked with Toga before, but was not involved in this current study.

"Even though plus 0.4 and plus 0.6 years of relative brain age may look small and not significant, these numbers are actually important, especially since they are associated with a corresponding and significant worse cognitive function," Barisano says.