"Even moderate drinking can damage the brain," The Guardian reports. A new study, involving brain scans and cognitive testing, suggests that moderate drinking, over many years, could damage areas of the brain linked to memory and cognitive function.
The results showed that the higher the amount of alcohol consumed a week, the higher the risk of damage to certain areas in the brain, including those involved in memory.
This association was not found for "light" drinkers (people who consume between one and seven units a week). However, the scan was only performed once so we don't know if and when the brain structures changed or whether the changes were caused by other factors.
The researchers also found that people drinking alcohol in moderate or heavy quantities (over seven units a week) had a faster decrease in ability to name words beginning with the same letter but no difference for any other brain test.
Despite anecdotal reports to the contrary, many of which were promoted by the media, no protective effect of "light" drinking on cognitive function compared to completely abstaining from alcohol was found.
UK guidelines on alcohol were changed last year to reflect evidence that there is no such thing as a "safe level" of drinking; just a level when harms were at their lowest.
The guidelines now recommend that both men and women drink no more than 14 units of alcohol per week – the equivalent of around six pints of beer, and this study seems to support these guidelines.
Where did the story come from?
The study was carried out by researchers from the University of Oxford and University College London in the UK and was funded by the UK Medical Research Council, the Gordon Edward Small's Charitable Trust and the HDH Wills 1965 charitable trust. There were no reported conflicts of interest.
The UK media's reporting of the study was generally accurate, with the noticeable exception of the headline printed by The Sun, which claimed that "less than a pint a day means you're 'THREE TIMES more likely to develop early signs of Alzheimer's'". This is not an accurate reflection of the study findings as none of the participants had developed Alzheimer's disease.
What kind of research was this?
This was a prospective cohort study, following adults over 30 years to look at their weekly alcohol intake and cognitive performance over time and brain structure at the end of the study.
This type of study is best for looking at things like alcohol intake, as a randomised controlled trial where participants get allocated to a weekly alcohol intake level would be unethical. Following people over time and asking them to record their weekly intake is a much better way of studying the effects of alcohol on the brain and cognitive performance.
What did the research involve?
Researchers took 550 participants who were already enrolled in the Whitehall II study, a study that started in 1985 aiming to investigate the relationship between socioeconomic status, stress and cardiovascular health in civil servants.
Over 30 years sociodemographic, health and lifestyle variables (including alcohol use) were measured at intervals:
- phase I: 1985-88
- phase 3: 1991-93
- phase 5: 1997-99
- phase 7: 2003-04
- phase 9: 2007-09
- phase 11: 20011-12
Average alcohol use across the study was calculated as mean consumption a week averaged over all study phases. Participants were categorised as:
- "abstinent" if they consumed less than one unit of alcohol a week
- "light drinking" was defined as between one and less than seven units
- "moderate drinking" was defined as seven to less than 14 units a week for women and seven to less than 21 units for men
- "unsafe drinking" was defined according to pre-2016 (21 units a week for men and 14 units for women) and newly revised UK Department of Health guidelines (more than 14 units for men and women)
The researchers looked at brain structure including grey matter density, hippocampal atrophy and white matter by carrying out a magnetic resonance imagining (MRI) scan on participants at the end of the study (between 2012 and 2015).
Grey matter consists of a range of specialised nerve cells while white matter mainly consists of cells that help send signals through the brain. The hippocampus is an area of the brain involved with memory.
Cognitive function was also assessed at phases 3, 5, 7, 9 and 11 and at the time of scanning with tests including :
- semantic fluency – naming as many words as possible in the same category, such as animals
- lexical fluency – naming as many words beginning with same letter as possible
- performance on the Montreal cognitive assessment – which checks for mild cognitive impairment
- trail making test – connecting dots to look at visual search speed and mental flexibility
- Rey-Osterrieth complex figure test – reproduce a complex line drawing
- Hopkins verbal learning test – asking a person to remember and then recall a short list of words
- Boston naming test – to measure word recall and naming ability
- digit substitution test – matching symbols with their corresponding digits
Age, sex, education, smoking, social activity, blood pressure, smoking, history of cardiovascular events and cardiovascular drugs were assessed by questionnaire. Social class, lifetime history of major depressive disorder and drug use were also taken into account.
What were the basic results?
Median alcohol consumption was 11.5 units a week for men and 6.4 units for women and this did not increase significantly over the phases of the study for the group as a whole.
- Compared with abstinence, greater alcohol consumption was associated with increased odds of hippocampal degeneration in a dose dependent way – the more alcohol, the more atrophy.
- In light drinkers, (one to less than seven units a week) there was no difference in brain structure compared with those who abstained from alcohol.
- Those consuming more than 30 units a week were at five times higher risk of right sided hippocampal atrophy compared with abstainers (odds ratio [OR] 5.8, 95% confidence interval [CI] 1.8 to 18.6). The total number of people this was based on was small though; 24 out of 31 heavy drinkers had signs of atrophy compared to 13 out of 37 abstainers.
- Overall, moderate drinkers (14 to less than 21 units a week) had a three times higher risk of hippocampal atrophy compared with abstainers (OR 3.4, 95% CI 1.4 to 8.1).
- Women who drank moderately had no significant difference with abstainers, but men who drank moderately did.
- Of the 10 tests of brain function, only one result was significant; lexical fluency.
- Higher alcohol consumption predicted a faster decline in lexical fluency. Over the 30 years, people drinking seven to less than 14 units experienced 14% greater reduction in lexical fluency, those drinking 14 to less than 21 units 17% greater reduction and those drinking more than 21 units a 16% greater reduction than those who abstained from alcohol.
How did the researchers interpret the results?
The researchers concluded: "the finding that alcohol consumption in moderate quantities is associated with multiple markers of abnormal brain structure and cognitive function has important potential public health implications for a large sector of the population."
They further add that their 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. Alcohol might represent a modifiable risk factor for cognitive impairment, and primary prevention interventions targeted to later life could be too late."
The results in this study indicate a link between alcohol intake – even moderate intake – and structural changes in the brain and decline in the ability to list words beginning with the same letter. The majority of cognitive functioning tests showed no association with alcohol intake.
This 30 year-long study has the ability to investigate changes in cognitive ability over a long period of time but does have some limitations:
- The participants are all people who were civil servants in the 1980s and were mostly male and more middle class and higher IQ than the general population, meaning results might not be applicable to the UK as a whole.
- The effect of hippocampal atrophy was found in men and not women which may be down to the lower sample size of women and that few of them drank heavily.
- The information on alcohol intake was self-reported and therefore might be inaccurately reported by participants.
- It is difficult to link brain structure with alcohol intake when it might have been down to other confounding factors such as intelligence, cognitive stimulation and other lifestyle factors.
- The MRI scan only took place once, at the end of the study, so it is difficult to tell if and when any changes in brain structure took place and rule out other influencing factors.
The structural changes in the brain were found to be statistically significant but it is not known if these changes are clinically significant – if they actually impact health in the long run.
As we are still unsure of the potential effect of alcohol on our brains, and the well known increased risks of cancer and liver disease, it is wise not to exceed the weekly UK limit of 14 units for both men and women.