How drinking affects your dementia risk – and what studies say about moderate alcohol use

Researchers are still investigating what alcohol does to the brain, and what (if any) amount is safe.

(Art: The New York Times)

In 2003, a study published in the prestigious Journal of the American Medical Association reported that having two or more alcoholic beverages per day was associated with a 22 per cent increased risk of dementia. But people who drank less than that had up to a 54 per cent lower risk, compared with people who didn’t drink at all.

“I remember reading that JAMA paper 20-some odd years ago and thinking, I really ought to try and have a glass of wine every day,” said Dr Joel Gelernter, a professor of psychiatry, genetics and neuroscience at the Yale University School of Medicine.

That study wasn’t the only one to suggest that moderate alcohol consumption was beneficial for the brain: Observational research has consistently shown that light-to-moderate drinkers have a lower risk of dementia compared with nondrinkers.

“This idea of the J-shaped curve was really pretty darn reproducible in many studies,” said Dr Kristine Yaffe, a professor of psychiatry, neurology and epidemiology at the University of California, San Francisco. But, she added, “I think more recently, people have debunked that J.”

Indeed, researchers have come to understand that the health benefits attributed to a daily glass of wine are largely a mirage. People who drink in moderation tend to have more advantages in life than people who abstain (such as having higher socioeconomic status, more years of education and generally better health), and experts think that explains their lower risk for dementia, not the alcohol itself.

The evidence that heavy drinking (often defined as more than two drinks a day) can damage the brain and increase the risk of dementia has also continued to accumulate. But experts are still learning exactly how it happens and at what amount harms start to occur.

HEAVY DRINKING AND THE BRAIN

Experts have a few theories about how chronic excessive alcohol use hurts the brain. Research, much of it conducted on animals and human cells in a lab, indicates that alcohol can induce oxidative stress in the brain and disrupt the brain’s immune system, triggering harmful inflammation. Both oxidative stress and inflammation are associated with dementia.

Alcohol affects the brain indirectly, too. Heavy drinkers have an increased risk of high blood pressure and stroke, and blood vessel damage is a key contributor to vascular dementia. People who drink a lot also tend to have other unhealthy habits that can harm the brain, like smoking or a poor diet.

At the most extreme, some people with alcohol use disorder develop Wernicke-Korsakoff syndrome, a form of dementia caused by a severe thiamine (Vitamin B1) deficiency stemming from chronic heavy alcohol use.

“There’s multiple different pathways” through which alcohol can damage the brain, said Louise Mewton, an associate professor studying alcohol use at the University of Sydney. And, she added, “it may be all of these acting at once. The literature certainly is not settled.”

MODERATE DRINKING AND THE BRAIN

With lower levels of alcohol consumption, it’s less clear when and how the brain is affected. And because most studies on people’s drinking habits find that misleading J-curve, scientists have had to get creative with their research methods.

A few studies looking at brain volume have indicated that damage may happen even with light-to-moderate drinking. One large 2022 study from the United Kingdom found that having an average of eight drinks a week was associated with slightly smaller brain volume than having an average of four per week. And the greater the alcohol consumption, the smaller the brain.

Dr Charlies DeCarli, a professor of neurology at the University of California, Davis, said there’s no evidence that moderate amounts of alcohol directly harm neurons. “What these newer studies indicate, though, is that there is some relationship” between small doses of alcohol and the brain.

But, he added, “brain volume does not necessarily translate directly into cognitive performance.”

Other research suggests that light-to-moderate drinking may be associated with some loss in cognitive functioning, even if it doesn’t qualify as dementia. Another UK study found that people who had as little as four drinks a week experienced a greater decline in language abilities over the course of 30 years compared with people who were abstinent. Again, the more people drank, the worse their cognition got.

Newer research looking at genetic predisposition to drinking alcohol has also produced sobering results. A study published in January found that when researchers used people’s self-reported drinking habits to assess dementia risk, the typical J-curve emerged. But when they repeated the analysis using genes that predict drinking behaviour (whether someone is genetically more likely to drink a lot, a little or not at all), dementia risk increased even at low levels of predicted alcohol consumption.

Dr Gelernter, who was involved in the genetics study, said he now thinks there is a linear relationship between alcohol consumption and risk for cognitive decline. But the research hasn’t prompted him to abstain entirely. “I certainly no longer try to have a glass of wine every day, but I haven’t stopped,” he said. Although “it was much nicer when we said, ‘I’m doing it for my health,’” he added.

By Dana G Smith © The New York Times Company

The article originally appeared in The New York Times .

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研究人员仍在调查酒精对大脑的影响，以及（如果有的话）安全的饮酒量是多少。

（图片来源：《纽约时报》）

2003年，发表在权威医学期刊《美国医学会杂志》上的一项研究报告称，每天饮用两杯或两杯以上酒精饮料会使患痴呆症的风险增加22%。但与完全不饮酒的人相比，饮酒量低于此标准的人患痴呆症的风险最多可降低54%。

“我记得二十多年前读过那篇发表在《美国医学会杂志》上的论文，当时我就想，我真的应该尝试每天喝一杯葡萄酒，”耶鲁大学医学院精神病学、遗传学和神经科学教授乔尔·格伦特博士说。

那项研究并不是唯一表明适量饮酒对大脑有益的研究：观察性研究一直表明，与不饮酒者相比，轻度至中度饮酒者患痴呆症的风险较低。

“这种J形曲线的说法在很多研究中都得到了很好的重复验证，”加州大学旧金山分校精神病学、神经病学和流行病学教授克里斯汀·亚菲博士说。但她补充道，“我认为最近人们已经驳斥了这种J形曲线的说法。”

事实上，研究人员已经认识到，每天一杯葡萄酒带来的健康益处很大程度上是一种假象。适量饮酒者往往比滴酒不沾者拥有更多生活优势（例如更高的社会经济地位、更长的受教育年限和更佳的健康状况），专家认为，这才是他们患痴呆症风险较低的真正原因，而非酒精本身。

越来越多的证据表明，酗酒（通常定义为每天超过两杯酒）会损害大脑并增加患痴呆症的风险。但专家们仍在研究其具体机制以及饮酒量达到多少才会开始造成损害。

酗酒与大脑

专家们对长期过量饮酒如何损害大脑提出了一些理论。大量研究（其中许多是在实验室中对动物和人体细胞进行的）表明，酒精会诱导大脑氧化应激，扰乱大脑的免疫系统，引发有害的炎症。氧化应激和炎症都与痴呆症有关。

酒精也会间接影响大脑。酗酒者患高血压和中风的风险更高，血管损伤是血管性痴呆的主要诱因。此外，酗酒者往往还有其他一些不健康的习惯，例如吸烟或饮食不健康，这些都会损害大脑。

在最极端的情况下，一些患有酒精使用障碍的人会发展成韦尼克-科尔萨科夫综合征，这是一种由长期大量饮酒导致的严重硫胺素（维生素 B1）缺乏引起的痴呆症。

悉尼大学研究酒精使用的副教授路易丝·缪顿表示，“酒精可以通过多种不同的途径损害大脑”。她补充说，“也可能是所有这些途径同时起作用。目前相关文献尚未得出定论。”

适度饮酒与大脑

酒精摄入量较低时，大脑何时以及如何受到影响尚不明确。而且，由于大多数关于人们饮酒习惯的研究都呈现出容易误导的J形曲线，科学家们不得不创新研究方法。

一些关于脑容量的研究表明，即使是少量或适量饮酒也可能造成脑损伤。英国一项2022年的大型研究发现，平均每周饮酒八次与脑容量略小于平均每周饮酒四次有关。而且，饮酒量越大，脑容量越小。

加州大学戴维斯分校神经病学教授查理斯·德卡利博士表示，没有证据表明适量饮酒会直接损害神经元。“不过，这些新研究表明，少量饮酒与大脑之间存在某种关联。”

但他补充说，“大脑体积并不一定能直接转化为认知能力。”

其他研究表明，即使饮酒量不大，适度饮酒也可能导致认知功能下降，即使未达到痴呆症的程度。英国另一项研究发现，与滴酒不沾的人相比，每周饮酒仅四杯的人在30年间语言能力下降更为明显。同样，饮酒越多，认知能力下降得越厉害。

针对饮酒遗传倾向的最新研究也得出了令人警醒的结果。今年1月发表的一项研究发现，当研究人员使用人们自我报告的饮酒习惯来评估痴呆风险时，出现了典型的J型曲线。但当他们使用预测饮酒行为的基因（即某人是否天生更容易大量饮酒、少量饮酒或完全不饮酒）重复分析时，即使在预测的饮酒量较低的情况下，痴呆风险也会增加。

参与这项遗传学研究的格伦特博士表示，他现在认为饮酒量与认知能力下降风险之间存在线性关系。但这项研究并没有促使他完全戒酒。“我当然不再每天都喝一杯葡萄酒了，但我并没有完全停止饮酒，”他说。他还补充道：“虽然以前我们说‘我是为了健康才喝酒’的时候感觉好多了。”

作者：达娜·G·史密斯 © 纽约时报公司

本文最初发表于《纽约时报》。

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