REVIEW OF: Topiwala A et al, PLOS Medicine2022;19(7):e1004039

STUDY TYPE: Cohort study

For many years, the going wisdom has been that moderate alcohol intake is not harmful—and may even enhance health. However, more recent research has called this into question. This study looked at the effects of moderate alcohol consumption on brain iron levels and cognitive functioning. 

Prior research demonstrated increased iron accumulation in the brains of heavy drinkers (Juhás M et al, Neuroimage 2017;148:115–122). Could even moderate alcohol use result in higher iron levels in the brain, leading to cognitive problems? This observational study attempted to answer this question using data from the UK Biobank cohort of over half a million people.

The authors examined past health data of 20,729 people; the average age of the sample was 55 years, and 48.6% were women. Brain iron levels were measured using MRI, and an abdominal MRI checked for iron deposition in the liver and corroborated iron overload. Alcohol habits were investigated with questionnaires. The authors attempted to control for the effects of occupation, education, hypertension, menopause, and other variables on iron levels. Executive function, fluid intelligence, and reaction time were measured with the Trail-Making Test, puzzle tests, and a “Snap” card game, respectively. 

Among the cohort, 95% self-identified as current drinkers, 2.4% had discontinued drinking, and only 2.7% were never drinkers. The average alcohol consumption was 17.7 units weekly, which is more than the UK low risk guidelines (less than 14 units weekly). Drinking more than seven units weekly (or four standard drinks weekly in the US) was associated with increased iron in the basal ganglia. Higher levels of iron in the basal ganglia were associated with poorer executive function, fluid intelligence, and reaction times. Additionally, the authors found an alcohol-age interaction, suggesting that alcohol may magnify the effects of age on iron accumulation in the brain.

The study had some limitations. Alcohol use was collected through self-reporting, and the models of iron in the brain were not robust enough to suggest it as a singular or primary cause of cognitive dysfunction. The authors also acknowledged that myelin may alter imaging markers, as iron and myelin share indistinguishable features on MRI. 

Carlat Take

This big-data study on iron’s relationship with alcohol intake and the brain looks impressive from the outset. It supports the idea that there may not be a “safe” amount that patients can regularly drink. For optimum brain health, we strongly recommend reducing alcohol consumption, along with other interventions such as increasing exercise and cognitive engagement.