Even moderate levels of alcohol consumption are associated with an increased risk of adverse brain outcomes and a steeper decline in cognitive skills, finds a study published by the British Medical Journal (BMJ) on June 6.
Heavy drinking is known to be associated with poor brain health, but few studies have examined the effects of moderate drinking. A team of researchers from the University of Oxford and University College London investigated whether moderate alcohol consumption had any favorable or adverse associations with brain structure and function.
The authors point out that their study is observational, hence no firm conclusions can be drawn about cause and effect, and say some limitations could have introduced bias. However, they conclude that “Alcohol might represent a modifiable risk factor for cognitive impairment, and primary prevention interventions targeted to later life could be too late.”
The researchers added, “Our findings support the recent reduction in UK safe limits and call into question the current US guidelines, which suggest that up to 24.5 units a week is safe for men, as we found increased odds of hippocampal atrophy at just 14–21 units a week, and we found no support for a protective effect of light consumption on brain structure.”
One unit of alcohol is what one might find in one 25ml single measure of whisky, or a third of a pint of beer, or half a standard glass of red wine.
In a linked editorial, Killian Welch, consultant neuropsychiatrist at the Royal Edinburgh Hospital, says these findings “strengthen the argument that drinking habits many regard as normal have adverse consequences for health.”
The study’s authors used data on weekly alcohol intake and cognitive performance measured repeatedly over 30 years (from 1985 to 2015) for 550 healthy men and women who were taking part in another study, which evaluated the impact of social and economic factors on the long-term health of around 10,000 British adults.
Participants had an average age of 43 at the start of the study and none were alcohol dependent. Brain function tests were carried out at regular intervals. At the end of the study (2012-15), participants underwent magnetic resonance imaging (MRI) brain scans.
Several factors that could have influenced the results (known as confounding) were taken into account, such as age, sex, education, social class, physical and social activity, smoking, stroke risk and medical history.
After adjusting for these confounders, the researchers found that higher alcohol consumption over the 30-year study period was associated with increased risk of ‘hippocampal atrophy’—a form of brain damage that affects memory and spatial navigation.
While those consuming over 30 units a week were at the highest risk, compared with abstainers, even those drinking moderately (14 to 21 units per week) were three times more likely to have hippocampal atrophy compared with abstainers.
Moreover, there was no protective effect of light drinking (up to seven units per week) over abstinence.
Higher consumption was also associated with poorer white matter integrity (critical for efficient cognitive functioning) and faster decline in language fluency (how many words beginning with a specific letter can be generated in one minute). Yet no association was found with semantic fluency (how many words in a specific category can be named in one minute) or word recall.