LIGHT drinking helps prevent dementia, and now we may know why: it revs up the brain鈥檚 waste disposal system.
Brain cells are surrounded by a network of ultra-thin tubes that flush toxins and cell waste products away. Work in mice shows that low levels of alcohol stimulate this system, while higher amounts hinder it.
If the findings apply to people, the low levels would be equivalent to about two units of alcohol a day, which is about a pint of beer or a medium glass of wine.
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Alcohol has been getting a bad press lately. Excessive drinking causes liver damage and has been linked with several kinds of cancer. In the UK, the recommendation for how much it is safe to drink has been cut, with both men and women advised to stick to 14 units or fewer a week. The latest UK government report said even drinking at very low levels carries some risk. However, this relates to a slightly higher rate of cancers that are fairly rare 鈥� such as those of the oesophagus.
When it comes to more common conditions, such as dementia, total abstention from alcohol carries a slightly higher risk than low to moderate drinking. But it was unclear why.
The reason may be the brain鈥檚 waste disposal system, known as the glymphatic system, which was only discovered in 2012. We know it ramps up its activity during sleep. Among the toxins it clears is a protein called beta-amyloid, which makes up the sticky plaques found in the brains of people with Alzheimer鈥檚 disease. Some studies have suggested that long-term sleep disruption may contribute to Alzheimer鈥檚 by causing amyloid build-up.
鈥淎bstention from alcohol causes a slightly higher risk of dementia than low to moderate drinking鈥�
Iben Lundgaard of the University of Rochester in New York and her colleagues looked at the effects of alcohol on this network, by injecting a dye into mouse brains then removing them half an hour later to see how much had got into the tubes.
Low doses of alcohol boosted the amount cleared by 40 per cent compared with mice that had no alcohol. Intermediate and high doses had the opposite effect, cutting it by about 30 per cent. It is unclear how much that would affect people鈥檚 risk of Alzheimer鈥檚.
Roxana Carare of the University of Southampton, UK, says that the reason a low dose of alcohol has this effect may be because it raises the heart rate, and the pumping of blood helps drive fluid through the glymphatic system. 鈥淏ut there鈥檚 a lot we still don鈥檛 know about the normal functioning of the glymph system. We don鈥檛 know how this translates to humans.鈥�
At the Federation of European Neuroscience Societies meeting in Berlin last month, Lundgaard said that light drinking does seem to benefit the glymph system, but that more data would be needed before people make decisions about how much they drink based on this work, especially as it was in mice: 鈥淚 think that would be a little bit too soon.鈥�
Lundgaard says that as well as considering how alcohol affects their risk of Alzheimer鈥檚, people might also want to consider the effect on cancer.
This article appeared in print under the headline 鈥淎 few drinks might help stave off dementia鈥�
