In a paper published online today in the leading international journal "Neurology", lead author Winthrop Professor Osvaldo Almeida, research director at The University of Western Australia's Centre for Health and Ageing, found that alcohol itself is not a direct cause of cognitive impairment.
"Heavy alcohol consumption is known to be detrimental to health, so these results were counter intuitive," Professor Almeida said.
He said that a commonly held belief, based on previous association studies, was that excessive alcohol use is a cause of cognitive impairment. However, the link had never actually been proven.
He and his fellow researchers decided to test the theory by examining a gene known to be responsible for how successfully a person is able to metabolise alcohol - that is, their degree of tolerance for alcohol.
The researchers used a study design known as Mendelian randomisation to analyse the genetic data from 3542 men between the ages of 65 and 83 years. Mendelian randomisation incorporates genetic information into traditional epidemiologic methods.
Participants were asked about their alcohol consumption over the previous year. They were classified as abstainers, occasional drinkers or regular drinkers depending on the number of standard drinks they consumed per week. Consuming more than 35 standard drinks per week was classified as alcohol abuse.
Their degree of ‘cognitive impairment' - defined as a decrease in the brain's processing speed and efficiency as well as a deterioration in memory - was measured with a validated scale 6 years later.
Professor Almeida said that if heavy alcohol use is a direct cause of cognitive impairment, then people with the genetic variant that makes them avoid alcohol should have lower risk of cognitive impairment later in life. However, that was not the case.
The study concluded that alcohol consumption, including heavy regular drinking and abuse, was not a direct cause of cognitive impairment in later life. Rather, indirect causes - such as poor nutrition and head injury - were more likely to be responsible for the association between alcohol abuse and cognitive impairment.
In addition, the authors wrote: "Our results are consistent with the possibility, but do not prove, that regular moderate drinking decreases the risk of cognitive impairment in older men."
Professor Almeida said the study was limited to older men and it was unclear if the results could be generalised to other age groups or women. These results contribute to improve our understanding of the mechanisms that contribute to cognitive decline as people age.
This research is part of the Health In Men Study (HIMS), which has been following a group of men living in Perth, Western Australia since 1996. The HIMS study is the largest study of ageing men in Australia.