What alcohol is doing to your brain - and how much is a safe amount

Drinking habits that harm your liver may also be quietly shrinking your brain. Photo / 123RF

It’s not just your liver you should worry about - alcohol has been found to change the anatomy of your brain. Here’s what you need to know.

At the end of a busy week, I’m dreaming of getting home, opening the fridge and pouring myself a glass of a crisp, white wine. On nights out with friends, I look forward to sipping on cocktails. Inevitably, the night ends with a couple of shots.

When too many of these occasions cluster together, I always commit to cutting back the following week “to give my liver a break”. That’s the only organ I ever pay much mind to when it comes to drinking, as, famously, alcohol kills off liver cells. I’m guilty, as I presume many others are, of not thinking about how drinking is hitting my brain.

“I don’t think the brain features in most people’s thinking about alcohol at all,” agrees Dr Anya Topiwala, who studies the effect of alcohol on the brain at the University of Oxford. “Maybe it’s because the research has been contradictory and the message about a glass of red wine a night being good for the brain has propagated - it’s what we all want to believe.”

“However, I don’t believe it biologically,” says Topiwala. “I can’t see a mechanism by which a small amount of alcohol will protect the brain. When we’ve done in-depth studies using brain imaging, we haven’t found that at all. We found no protective effects. We only found harmful effects.” So, just how much are our drinking habits harming our brain?

Seven units of alcohol per week is enough to start shrinking your brain, impacting areas critical for memory and cognition. Photo / 123RF

Seven units per week: Brain starts to shrink

Three 175ml glasses of wine, three pints of 4% beer or seven single shots of spirits.

As soon as alcohol passes our lips, it starts to be absorbed. First in our mouth, then throughout the rest of our digestive system. This includes going through the liver and into the bloodstream. Within five to 10 minutes, it reaches the brain.

This is down to ethanol molecules, the type of alcohol in beer, wine and spirits, being so small. “Although there’s a barrier between our blood and the brain [that protects from harmful substances getting in], ethanol can easily diffuse through,” Topiwala explains.

If you drink more than seven units per week, which is half the recommended upper limit in the UK, it leads to changes in the anatomy of the brain. “People have smaller brains, literally,” she says. “We noticed this in their hippocampus - the part of the brain that is really important for memory. It is also one of the earliest regions affected by Alzheimer’s.”

Just seven units a week can also lower levels of grey and white matter - tissue that makes up the brain. “If you think of brain cells as electrical cables, the white matter is the outer cable and the grey matter is the wire inside those cables,” says Topiwala. “We’ve found that the white matter - the quality of that insolation around the wires - is lower in people who drink seven units or more per week.”

While studies are yet to confirm the exact cause of these effects, scientists believe alcohol is killing our brain cells, forcing the organ to become smaller and damaging how it functions.

One study from Topiwala and her colleagues which looked at drinking habits and memory test results among 550 people over a 30-year period found people who had more than seven units a week had a faster decline in memory. “They had to name as many words as they could within a minute, beginning with a specific letter. It’s quite a hard task that engages the front part of your brain for problem solving. Those who had more alcohol got worse faster.”

Each of these findings are dose-dependent, she explains. “The more you drink, the worse it gets [in terms of brain shrinkage, less white matter and cognitive test results]. We can detect these changes at seven units but the effect is more dramatic as alcohol intake increases.”

White and grey matter in the brain are both affected by alcohol, with regular drinking reducing the integrity of these critical tissues. Photo / 123RF

14 units per week: Iron accumulates in the brain

Six 175ml glasses of wine; six pints of 4% beer or 14 single shots of spirits.

An additional worry that kicks in when people drink more than 14 units per week is higher brain iron markers, Topiwala says.

Iron accumulates in people’s brain as part of ageing, but research suggests alcohol can further fuel this process. This is bad news, as it is thought the mineral damages brain cells and exacerbates cognitive decline. Too much iron in the brain has also been linked to Alzheimer’s and Parkinson’s.

“The more you drink, the more you get iron in your blood, liver and brain, which then leads to memory problems,” Topiwala explains.

Topiwala and colleagues have found iron accumulated in the basal ganglia at 14 units per week - the brain region responsible for movement. Those with higher iron levels in this part of the brain were slower at completing problem-solving tasks, results showed. “We can start seeing this effect at 14 to 21 units per week, and then it’s even more extreme at 21 to 28, and alcoholics have the highest levels of all,” she adds.

28 units per week: At risk of long-term brain damage

12 175ml glasses of wine; 12 pints of 4% beer or 28 single shots of spirit.

Women who drink more than 28 units a week and men who have more than 35, over a period of five years, are at risk of a type of irreversible brain damage called Korsakoff syndrome, Topiwala says.

“It’s thought to be down to a thiamine deficiency (also known as vitamin B1),” she explains. Alcohol prevents the gut from absorbing enough of the vitamin, which brain cells need to work properly, meaning too much is lost through urine.

This can lead to a specific type of brain inflammation called Wernicke encephalopathy. “People who are very deficient can become confused, develop abnormal eye movements and unsteady walking,” she says. “If they are not treated quickly with thiamine, it can progress to Korsakoff syndrome, which is essentially a severe dementia.”

“People who have been drinking heavily can get this in their 40s or 50s and end up in nursing homes,” Topiwala says. “But you have to be drinking really quite heavily for that - above 28 units for women and 35 for men over a period of five years.

Binge drinking is particularly harmful, as the repeated cycle of alcohol exposure and withdrawal intensifies brain damage. Photo / 123RF

So how much should we drink?

“Alcohol is a toxin for your brain and it basically just kills brain cells, so it’s just how much you’re willing to do that,” says Topiwala. “I have one small glass with dinner a few times a week. For me, that’s the kind of balance that seems right. We all accept some risk in our life. If you want zero risk from alcohol on your brain, don’t drink anything.”

Cutting out binge drinking behaviour can also help. “It’s certainly worse to binge,” she says. “It’s thought that the repeated cycle of soaking your brain in alcohol and then withdrawing from alcohol is worse than steady exposure.”

But, ultimately, don’t kid yourself that moderate drinking won’t harm your brain health. “Whatever you can do to cut down is going to help you,” Topiwala adds.