Drinking alcohol, even at moderate levels, can have a negative impact on brain function. Scientists have now shown it is associated with a degeneration of the hippocampus, the part of the brain that helps memory and spatial navigation.

Alcohol consumption has been linked with a wide range of health conditions, but at moderate levels – between 9 and 18 units - it has long been considered harmless (see video below for guidance about units). Some studies have even shown that drinking moderately could have a protective effect against cardiovascular disease and diabetes.

However, the long term effects of moderate drinking on cognitive function and brain activity are less well understood.

Although some studies have argued that light-to-moderate drinking can reduce the risk of dementia and cognitive decline, brain imaging studies have so far come up with contradictory results.

The research now published in the BMJ investigates the relationship between moderate alcohol consumption and brain structure and function using MRI scans to study the hippocampus' degeneration (or hippocampal atrophy), grey matter density and white matter microstructure.

The scientists worked with 550 participants, both men and women, with a mean age of 43. Their alcohol intake and cognitive performance were measured repeatedly over thirty years and MRI scans were performed at the end, between 2012 and 2015.

They found that people who had been drinking moderately showed alterations to their brain structures, including hippocampal atrophy. On the long term, there is a potentially higher risk of cognitive decline and neurodegenrative diseases.

"The types of scans we did allowed us to look closely at the brain. We expected to see a protective effect from moderate alcohol consumption over the years, like some studies have previously shown, but we were surprised to find that this was not the case", lead author Anya Topiwala clinical lecturer in old age psychiatry at the University of Oxford, told IBTimes UK.

"One of our main findings was that the hippocampus of people who drink the most is smaller. This is an area of the brain that is associated with memory and hippocampus atrophy is one of the early markers of Alzheimer's disease, so this is a concern".

A clear public health message

These findings back up the recent reduction in alcohol guidance in the UK to 14 units a week for men and women (about five pints of beer at 5% ABV strength).

They also question the current limits recommended in the US which suggest that up to 24.5 units a week is safe for men, as the research suggests increased odds of hippocampal atrophy at just 14-21 units a week.

It's interesting to note however that despite the structural changes to the brain observed on the scans, the participants did not yet show significant signs of cognitive decline.

Topiwala explained: "We only found a relationship between alcohol intake and one type of cognitive decline. One of the possible reasons we did not find more widespread associations might be that people who had greater IQ also drank the most.

"Whilst we attempted to control for this, it is possible that higher IQ might be associated with other behaviours we have not accounted for, such as dietary factors."

It's not possible at this stage then to show that moderate drinking causes dementia or other neurodegenrative diseases. That being said, it is still worth promoting a public health message that encourages a reduction in drinking.

"This robust study takes advantage of a large cohort to demonstrate that alcohol intake is associated with reduced brain volume and integrity. There was only a hint here that high alcohol intake results in poorer memory – an effect that could predispose to dementia.

"An observational study cannot truly prove that alcohol causes dementia, but the findings are in keeping with my clinical experience. The toll of high alcohol consumption on cognitive health, often evident to those of us who run memory clinics, is not widely acknowledged publicly", Dr Elizabeth Coulthard, Consultant Senior Lecturer in Dementia Neurology, University of Bristol, commented.

"Hopefully this research will contribute to a greater understanding of true safe limits for alcohol consumption that ensure protection from future dementia. Until we have further studies, the good news is that low alcohol intake was not associated with brain or memory decline in this sample."