The Nuance

A lot goes wrong with us, and particularly with our brains, when we don’t get enough sleep.

A single rough night leaves us feeling unfocused and groggy, while chronic poor sleep is a major risk factor for psychological and neurological disorders, including Alzheimer’s disease.

Experts have long understood that sleep plays a critical role in brain health. But until recently, they’d struggled to explain how poor sleep causes so much trouble. The discovery of a hidden waste-clearance system in the brain may finally provide the answer.

“We’ve learned that there are channels in the brain that allow for an influx of fluid that effectively rinses its tissues,” says Ysbrand van der Werf, PhD, a professor of functional neuroanatomy at Amsterdam University Medical Center in the Netherlands. This rinsing helps flush out unwanted cellular garbage, protein aggregates, and other toxins.

“These channels are always there, but one of the new insights is that they’re much more open during sleep,” van der Werf says. By some estimates, this waste-clearance system — which is known as the glymphatic system — is 10-times more active during deep sleep.

“To me, this is the biggest news in recent sleep research,” he adds.

Low doses of alcohol helped dilate blood vessels and otherwise shift the vasculature of the brain in ways that allowed waste-containing fluid to move more freely.

One of the types of junk the glymphatic system removes is a damaging protein that accumulates in the brains of people who have Alzheimer’s disease.

“We’ve shown in animal models that the glymphatic system is a key player in the transport of amyloid beta out of the brain via the cerebral spinal fluid,” says Iben Lundgaard, PhD, a senior lecturer at Lund University in Sweden.

Lundgaard was part of the research team that first discovered the glymphatic system a decade ago. Her group’s work appears to explain why chronic poor sleep is associated with neurological problems such as Alzheimer’s. Just as a city would gradually cease to function if its trash were left to pile up on street corners, uncleared metabolic garbage seems to slowly clog and suffocate the sleep-deprived brain.

But sleep isn’t the only thing that affects glymphatic function. Some of Lundgaard’s more-recent research suggests that modest amounts of alcohol also support the brain’s waste-clearance operations.

Following a dose of alcohol that was equivalent to two standard U.S. drinks, glymphatic activity increased by more than 25 percent, her study found. On the other hand, alcohol in higher doses had just the opposite effect. After the equivalent of eight drinks, glymphatic activity was significantly depressed.

Other researchers have observed these effects. In 2019, a team at the New Jersey Institute of Technology likewise found that low doses of alcohol seem to promote the clearance of brain waste via the glymphatic system.

On its own, this research might not merit much consideration. But prior work has found that people who consume alcohol in moderation may be protected from Alzheimer’s and other brain diseases.

A 2019 research review found consistent evidence that light-to-moderate drinking is associated with a decreased risk for both Alzheimer’s disease and other forms of dementia. In some cases, light drinking was associated with a more than 50% reduction in Alzheimer’s risk. This trend was reversed among those who drank heavily.

All the usual correlation-is-not-causation warnings apply here. But it’s possible that alcohol’s influence on the glymphatic system may partly explain these associations.

‘However significant the observed effects of alcohol on glymphatic function, they would never lead to a recommendation of drinking alcohol for health.’

How could alcohol support the glymphatic system? Lundgaard says that’s tricky. “If alcohol were a drug, we would call it a dirty drug because it has so many different effects, from the receptor level to the system level,” she says.

But she’s willing to venture a guess.

During deep sleep, some elements of neurochemical activity mellow in ways that appear to create more space for cerebral spinal fluid to flow through the brain, which facilitates its rinsing and refreshing action. Something like this may also be going on — to a lesser extent — when someone drinks a little alcohol. Drinking may relax or otherwise alter neurochemical activity in ways that facilitate glymphatic action, she says.

In line with this hypothesis, the New Jersey Institute of Technology researchers found that low doses of alcohol helped dilate blood vessels and otherwise shift the vasculature of the brain in ways that allowed waste-containing fluid to move more freely.

It’s important to highlight the limitations of these new findings.

For starters, this work involved animals, not people. The process of measuring glymphatic activity is not possible in human brains. (“It involves taking off a piece of the skull,” Lundgaard told me.)

However, her team assessed alcohol and glymphatic activity in pigs — an animal whose brain works similarly to a human’s. She says this work, coupled with things that can be studied in people, such as the flow and composition of cerebral spinal fluid as it enters and leaves the brain, indicate that the animal work on glymphatic activity is likely to hold up in humans.

I know that some people reading this are going to be PO’d at the suggestion that alcohol — even in small amounts — could be anything but poison.

Yes, alcohol is habit-forming, and the research is unanimous that alcohol in large quantities is unhealthy. Alcohol may also be uniquely risky if you’re dealing with mental health challenges, which many people are these days. And some work — notably a 2018 research review in The Lancet — has concluded that no amount of drinking should be considered safe.

But that Lancet study, as some doctors pointed out at the time, actually showed that the risks associated with a drink or two are so vanishingly small as to be irrelevant. Most of the research on light-to-moderate drinking — usually defined as no more than one drink a day for women or two for men — has tended to turn up either benefits or insignificant effects.

I think there’s an eagerness to apply stark good/bad labels to everything we do. Many of us disdain moderation and gravitate toward radical all-or-nothing approaches, usually to our detriment. Lately, alcohol seems to be coming in for this treatment.

The point here isn’t that people should drink. The evidence doesn’t support that advice, and no expert would give it. “However significant the observed effects of alcohol on glymphatic function, they would never lead to a recommendation of drinking alcohol for health,” says Amsterdam UMC’s van der Werf.

However, if you do drink, this new work seems to fall in line with a lot of prior research. Having a little alcohol now and then seems safe for most adults, and may even turn out to provide health benefits. Heavy drinking is dangerous. Use your best judgment.