Researchers, including those from Oxford University in the UK, analysed data on weekly alcohol intake and cognitive performance measured repeatedly over 30 years for about 550 healthy men and women.
Participants had an average age of 43 years at the start of the study and none were alcohol dependent.
Researchers carried brain function tests at regular intervals and at the end of the study participants underwent an MRI brain scan.
Several factors that could have influenced the results were taken into account, such as age, sex, education, social class, physical and social activity, smoking, stroke risk and medical history.
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While those consuming over 30 units a week were at the highest risk compared with abstainers, even those drinking moderately (14-21 units per week) were three times more likely to have hippocampal atrophy compared with abstainers, researchers said.
Researchers also found that higher consumption was 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).
The study was published in the journal The BMJ.