Did they correct for individuals who currently intake no alcohol but have a past history of alcohol consumption? My understanding is this is one of the ways past studies have skewed the results, because some people quit cold turkey but then live with the consequences of moderate or heavy drinking for years (or an entire lifetime) after that.
(I skimmed to the introductory paragraph where they talk about confounders, but don't see alcohol history listed as a confounder.)
In the summary section they talk briefly about this:
"It is reasonable to expect that the relationship we observe would differ in younger individuals who have not experienced the chronic effects of alcohol on the brain. An additional limitation stems from the self-reported alcohol intake measures in the UK Biobank, which cover only the year prior to participation. Such estimates may not adequately reflect drinking prior to the past year and are susceptible to reporting and recall bias.
Further, our analyses do not account for individuals with a past diagnosis of AUD. Earlier studies have shown that the brain shows some recovery with the cessation of drinking in individuals with AUD, but this varies with age and sex, and recovery might be incomplete. Thus, a past diagnosis of AUD would likely influence our results. We hope future studies will shed light on how a history of AUD with prolonged recovery is associated with brain structure in middle-aged and older adults."
Some version of their code is listed here[1] and it doesn't look like former alcohol consumption was accounted for. (Interestingly they have code to toggle inclusion/exclusion of people based on former alcohol consumption.) I didn't see it mentioned in the main text or the supplement either.
(I skimmed to the introductory paragraph where they talk about confounders, but don't see alcohol history listed as a confounder.)