Despite the joys that may come from a boozy Friday night, alcohol is bad for us. And not just in large quantities.

Recent studies have been warning that even a moderate amount of drinking is linked to cardiovascular issues and brain damage. A new study looking at over 36,000 adults has now put the boot in as well, finding that going from one to two drink 'units' per day is linked to a shrinking of brain matter – equivalent to two years of aging.

"These findings contrast with scientific and governmental guidelines on safe drinking limits," says psychiatry researcher Henry Kranzler, from the Penn Center for Studies of Addiction.

"For example, although the National Institute on Alcohol Abuse and Alcoholism recommends that women consume an average of no more than one drink per day, recommended limits for men are twice that, an amount that exceeds the consumption level associated in the study with decreased brain volume."

The US and European team of researchers looked at data from 36,678 adults (from middle-age and older) from the UK Biobank – a large, long-term observational study set up in the UK.

The scientists had access to the participants' self-reported number of 'units' per week or month (units are how the UK measures alcohol amount, and one US standard drink is around 1.75 units). The units per week and month were converted into units per day for the study. They also had access to MRI data for each of the participants, which helped them determine brain sizes in both the gray and white matter.

After controlling for factors such as age, BMI, and sex, the team found there was a negative association between alcohol intake and the brain structure of the participants. This was seen across the whole of the brain, but the largest volume changes occurred in three areas of the cortex, the brain stem, putamen, and the amygdala.

This occurred very strongly at higher levels of alcoholic consumption – the researchers found that at age 50, compared to those that didn't drink, those that had four units per day had a gray and white matter volume change equivalent to over ten years of extra aging.

But the team could also see a difference between those that had one drink a day and those that had two: for someone at age 50, that difference was two years' worth of aging in both gray and white matter.

"Most of these negative associations are apparent in individuals consuming an average of only one to two daily alcohol units," the team writes in their paper.

"Thus, this multimodal imaging study highlights the potential for even moderate drinking to be associated with changes in brain volume in middle-aged and older adults."

A number of recent studies have suggested that there's no okay amount of drinking, despite what we've been told in the past, and this study backs this up.

Importantly though, like many similar studies, this research can only show a correlation between alcohol use and brain changes. Because the research was observational, we can't tell if brain changes were because of the drinking, or if there's a factor that might have been missed. Although it's unlikely, it could even be that smaller brain sizes could cause more drinking.

But despite that, the team stresses that it doesn't hurt to cut back if possible, even if it's just one drink less a night.

"The people who can benefit the most from drinking less are the people who are already drinking the most," says University of Pennsylvania consumer neuroscience researcher Gideon Nave.

Probably worth keeping in mind for next weekend.

The study has been published in Nature Communications.