The End of Happy Hour? No Safe Level of Alcohol for the Brain

Megan Brooks

May 24, 2021

There is no safe amount of alcohol consumption for the brain; even moderate drinking adversely affects brain structure and function, according a British study of more 25,000 adults.

"This is one of the largest studies of alcohol and brain health to date," Anya Topiwala, DPhil, University of Oxford, Oxford, United Kingdom, told Medscape Medical News.

"There have been previous claims the relationship between alcohol and brain health are J-shaped (ie, small amounts are protective), but we formally tested this and did not find it to be the case. In fact, we found that any level of alcohol was associated with poorer brain health compared to no alcohol," Topiwala added.

The study, which has not yet been peer reviewed, was published online May 12.

Global Impact on the Brain

Using the UK Biobank, the researchers evaluated brain health on the basis of structural and functional brain MRI measures in 25,378 adults. Participants provided detailed information on their alcohol intake. The cohort included 691 never-drinkers, 617 former drinkers, and 24,069 current drinkers.

Median alcohol intake was 13.5 units (102 g) weekly. Almost half of the sample (48.2%) were drinking above current UK low-risk guidelines (14 units, 112 g weekly), but few were heavy drinkers (>50 units, 400 g weekly).

After adjusting for all known potential confounders and multiple comparisons, a higher volume of alcohol consumed per week was associated with lower gray matter in "almost all areas of the brain," Topiwala told Medscape Medical News.

Alcohol consumption accounted for up to 0.8% of gray matter volume variance. "The size of the effect is small, albeit greater than any other modifiable risk factor. These brain changes have been previously linked to aging, poorer performance on memory changes, and dementia," Topiwala said.

Widespread negative associations were also found between drinking alcohol and all the measures of white matter integrity that were assessed. There was a significant positive association between alcohol consumption and resting-state functional connectivity.

Higher blood pressure and body mass index "steepened" the negative associations between alcohol and brain health, and binge drinking had additive negative effects on brain structure beyond the absolute volume consumed.

There was no evidence that the risk for alcohol-related brain harm differs according to the type of alcohol consumed (wine, beer, or spirits).

A key limitation of the study is that the study population from the UK Biobank represents a sample that is healthier, better educated, and less deprived and is characterized by less ethnic diversity than the general population. "As with any observational study, we cannot infer causality from association," the authors note.

What remains unclear, they say, is the duration of drinking needed to cause an effect on the brain. It may be that vulnerability is increased during periods of life in which dynamic brain changes occur, such as adolescence and older age.

They also note that some studies of alcohol-dependent individuals have suggested that at least some brain damage is reversible upon abstinence. Whether that is true for moderate drinkers is unknown.

On the basis of their findings, there is "no safe dose of alcohol for the brain," Topiwala and colleagues conclude. They suggest that current low-risk drinking guidelines be revisited to take account of brain effects.

Experts Weigh In

Several experts weighed in on the study in a statement from the nonprofit UK Science Media Center.

Paul Matthews, MD, head of the Department of Brain Sciences, Imperial College London, noted that this "carefully performed preliminary report extends our earlier UK Dementia Research Institute study of a smaller group from same UK Biobank population also showing that even moderate drinking is associated with greater atrophy of the brain, as well as injury to the heart and liver."

Matthews said the investigators' conclusion that there is no safe threshold below which alcohol consumption has no toxic effects "echoes our own. We join with them in suggesting that current public health guidelines concerning alcohol consumption may need to be revisited."

Rebecca Dewey, PhD, research fellow in neuroimaging, University of Nottingham, Nottingham, United Kingdom, cautioned that "the degree to which very small changes in brain volume are harmful" is unknown.

"While there was no threshold under which alcohol consumption did not cause changes in the brain, there may a degree of brain volume difference that is irrelevant to brain health. We don't know what these people's brains looked like before they drank alcohol, so the brain may have learned to cope/compensate," Dewey said.

Sadie Boniface, PhD, head of research at the Institute of Alcohol Studies and visiting researcher at King's College London, said, "While we can't yet say for sure whether there is 'no safe level' of alcohol regarding brain health at the moment, it has been known for decades that heavy drinking is bad for brain health.

"We also shouldn't forget alcohol affects all parts of the body and there are multiple health risks. For example, it is already known there is 'no safe level' of alcohol consumption for the seven types of cancer caused by alcohol, as identified by the UK chief medical officers," Boniface said.

The study was supported in part by the Wellcome Trust, Li Ka Shing Center for Health Information and Discovery, the National Institutes of Health, and the UK Medical Research Council. Topiwala, Boniface, Dewey, and Matthews have disclosed no relevant financial relationships.

MedRxiv. Published online May 12, 2021. Full text

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