There is so much we still do not know about the nuances of alcohol consumption and cognitive decline. While we are well aware that chronic overuse is associated with chronic disease and an increased risk of early mortality1, there is compelling research indicating that mild to moderate intake of alcohol is beneficial in preventing dementia.2
What does the evidence show?
Many of the studies looking at lifetime alcohol use are hindered by methodology. Researchers may measure alcohol consumption at a single point in time or rely on recall, which is plagued by bias, especially in elderly individuals as they try to quantify a lifetime alcohol consumption. Despite these hindrances, there is growing consensus that the association between alcohol and cognitive outcomes is not linear but rather tends to follow a U or J shape curve. Low to moderate consumption confers benefits and reduces risk compared to chronic overindulgence or even extreme abstinence.2
Light to moderate alcohol intake is associated with a 30-40% decrease in the risk of dementia.3 On the other hand, complete or near-complete abstinence is associated with increased dementia. Sabia et al. conducted a three decade prospective cohort study of alcohol consumption and determined that alcohol abstinence during midlife was associated with a greater risk of dementia compared to consumption of 1-14 units of alcohol weekly.2 While the exact reason for this effect remains elusive, they suggest that there may be neuroprotective effects of alcohol or may increase the risk of cardiometabolic disease in midlife abstainers.2
How does alcohol affect the brain?
There is no clear consensus regarding the mechanism behind alcohol’s effect on the brain and dementia. Excessive alcohol use is associated with cardiac and metabolic disease, which in turn is associated with dementia. Research indicates that the vascular damage conferred by metabolic disease affects both the heart and the brain and may underlie this association.4 It interesting, however, that moderate amounts of alcohol consumption have been shown to have positive effects on high density lipoprotein cholesterol, apolipoprotein AI and fibrinogen, suggesting that there is some cardio- and neuro-protective effects of alcohol use that are non-linear.
How much is too much?
Unfortunately, there is quite a bit of confusion regarding the upper limit of safe alcohol consumption, and furthermore it is unclear exactly how this amount is affected by an individual’s age or sex. For example, alcohol moderation seems to be more “useful” in younger cohorts than those older than 60. Likewise, many guidelines suggest that men may safely consume more alcohol than women can.5 There remains a wide variation in alcohol consumption guidelines across different nations. The British guidelines recently reduced the recommended upper limit of alcohol from 21 units per week to 14 units per week for men, making it the same level as for women. However, the American guidelines (USDA) still suggest that men may safely consume up to 2 drinks per day compared to women’s one drink per day.
This guidelines are in stark contrast to research that shows drinking more than 12.5 units (100 grams) per week is associated with a lower life expectancy. Moreover, consuming more than 12.5 units per week is associated with an increased stroke risk1 and worsened dementia.5 Interestingly, if one were to follow the American guideline recommendation for men, one would have a 17% increased risk of dementia in the recent large longitudinal study by Sabia et al.2 On the other hand, despite showing increased risk among extreme abstainers, no guidelines recommend that abstainers should take up moderate alcohol use.
With the differing guidelines, unanswered questions regarding abstinence and alcohol, and the unclear mechanism of action of alcohol on mentation, we can agree that there is much that we do not know. While we keep struggling for consensus, it could just be that moderate alcohol use may protect against certain diseases, while causing others. Excessive alcohol seems bad all around, though the line between “excessive” and “high moderate” isn’t quite as clear as we’d like. On the other end of the spectrum, complete abstinence isn’t necessarily a cure all, either, with abstainers possibly missing out on some poorly defined benefits of low to moderate alcohol use. As healthcare providers, the best we can do is explain the risk to patients (what we know and that we don’t know everything) so they can make the best decision for themselves.
1. Wood AM, Kaptoge S, Butterworth AS, et al. Risk Thresholds for Alcohol Consumption: Combined Analysis of Individual-Participant Data for 599 912 Current Drinkers in 83 Prospective Studies. Lancet. 2018;391(10129):1513-1523. doi:10.1016/S0140-6736(18)30134-X
2. Sabia S, Fayosse A, Dumurgier J, et al. Alcohol Consumption and Risk of Dementia: 23 Year Follow-up of Whitehall Ii Cohort Study. BMJ. 2018;362:k2927. doi:10.1136/bmj.k2927
3. Winblad B, Amouyel P, Andrieu S, et al. Defeating Alzheimer’s Disease and Other Dementias: A Priority for European Science and Society. Lancet Neurol. 2016;15(5):455-532. doi:10.1016/S1474-4422(16)00062-4
4. Biessels GJ, Strachan MW, Visseren FL, Kappelle LJ, Whitmer RA. Dementia and Cognitive Decline in Type 2 Diabetes and Prediabetic Stages: Towards Targeted Interventions. Lancet Diabetes Endocrinol. 2014;2(3):246-255. doi:10.1016/S2213-8587(13)70088-3
5. Xu W, Wang H, Wan Y, et al. Alcohol Consumption and Dementia Risk: A Dose-Response Meta-Analysis of Prospective Studies. Eur J Epidemiol. 2017;32(1):31-42. doi:10.1007/s10654-017-0225-3