Objectives  To investigate whether moderate alcohol consumption has a favourable or adverse association or no association with brain structure and function.

Design  Observational cohort study with weekly alcohol intake and cognitive performance measured repeatedly over 30 years (1985-2015). Multimodal magnetic resonance imaging (MRI) was performed at study endpoint (2012-15).

Setting  Community dwelling adults enrolled in the Whitehall II cohort based in the UK (the Whitehall II imaging substudy).

Participants  550 men and women with mean age 43.0 (SD 5.4) at study baseline, none were “alcohol dependent” according to the CAGE screening questionnaire, and all safe to undergo MRI of the brain at follow-up. Twenty three were excluded because of incomplete or poor quality imaging data or gross structural abnormality (such as a brain cyst) or incomplete alcohol use, sociodemographic, health, or cognitive data.

Main outcome measures  Structural brain measures included hippocampal atrophy, grey matter density, and…