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Seven units of alcohol is equivalent to three pints of average-strength beer or five small glasses of lower-strength wine, according to the UK National Health Service (NHS).
The study, recently published in the journal PLOS Medicine, involved over 21,000 participants to analyse the links between alcohol consumption and brain iron levels.
Iron buildup in the brain has been associated with Parkinson’s and Alzheimer’s diseases and may be a contributing factor to the cognitive decline brought on by alcohol use.
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There is increasing evidence that even moderate alcohol use can have a negative impact on brain health, they said.
”In the largest study to date, we found drinking greater than 7 units of alcohol weekly associated with iron accumulation in the brain,” said Anya Topiwala of the University of Oxford.
”Higher brain iron in turn linked to poorer cognitive performance. Iron accumulation could underlie alcohol-related cognitive decline,” Topiwala explained.
The 20,965 volunteers from the UK Biobank provided information on their own alcohol consumption, and magnetic resonance imaging (MRI) was used to examine their brains.The average age of the participants was 55, and 48.6 per cent of them were female.
To determine the amounts of systemic iron, almost 7,000 people had their livers scanned using MRI. A series of basic tests were taken by each person to assess their cognitive and motor abilities.
Although 2.7 per cent of respondents identified as non-drinkers, the average weekly consumption was 18 units or about 7.5 cans of beer or 6 large glasses of wine.
The researchers discovered that alcohol consumption of over seven units per week was linked with markers of increased iron in the brain regions involved with motor control, procedural learning, eye movement, cognition, emotion, and other functions.
Iron accumulation in some brain regions was linked to worse cognitive function, they said.
A limitation of the study is that MRI-derived measures are indirect representations of brain iron, and could conflate other brain changes observed with alcohol consumption with changes in iron levels, the researchers said.
Given the prevalence of moderate drinking, even small associations can have a substantial impact across whole populations, and there could be benefits in interventions to reduce consumption in the general population, they added.