Review of: Sabia S et al, BMJ 2018;362:k2927

Type of study: Prospective cohort study

Excessive alcohol use is neurotoxic, but some studies have found that moderate alcohol intake might actually reduce the risk of dementia. Most of these studies, however, have focused on geriatric patients. What about the cumulative impact of alcohol over one’s lifetime? Would the same associations hold up?

In this landmark study (Whitewall II), researchers recruited British civil servants between 1985 and 1988. Subjects were 35–55 years old at the time of entry, and their alcohol intake was prospectively assessed every 4–5 years over the next several decades. New diagnoses of dementia were captured through a comprehensive review of the National Health Service electronic record database.

Among 9,087 subjects, 4.4% developed dementia over a mean follow-up period of 23 years. After adjusting for sociodemographic risk factors, those who drank in moderation (1–14 units/week) had the lowest rates of dementia. (Note: In the UK, a “unit” is defined as 8 g of alcohol so that a typical glass of wine or beer would consist of 2–3 units.) Abstinence was associated with a 1.5 times greater risk. A secondary analysis looking at trajectories of alcohol consumption over time provided independent confirmation that alcohol can indeed confer protective effects: The cohort of individuals who decreased their intake over time were also found to have a 1.5 times greater risk of dementia.

What about excessive alcohol use? Here, alcohol increased the risk of dementia in subjects who consumed more than 21 units/week. Beyond this threshold, the risk rose in a linear fashion so that each additional 7 units/week increased the risk of dementia by 17%. To compare apples to apples, somewhere between 28–35 units/week incurred a comparable degree of risk as complete abstinence—though, of course, the mechanisms by which these risks are incurred are undoubtedly distinct.

The researchers theorized that moderate alcohol consumption may reduce the risk of dementia through its beneficial effects on the cardiovascular system, inflammation, and insulin sensitivity.

TCPR’s Take
The relationship between alcohol and dementia appears to follow a checkmark (α) pattern (often referred to as “J-shaped”). The risk is elevated with abstinence, decreases with moderate consumption (1–14 units/week), and then increases in a linear fashion with excessive intake. Many editorials have warned that moderate drinking shouldn’t be taken up based on the results of this study, and caution is certainly warranted given alcohol’s multiple detrimental effects. But let’s also put the study’s finding in perspective: If a medication was developed that produced such impressive results, it almost certainly would be trumpeted as the medical breakthrough of the decade.