Dementia is among the greatest concerns of the aging population worldwide, as it involves a loss of mental and physical independence. Alcohol intake has been considered a risk factor for dementia. The fact that it is modifiable makes it of particular interest.
A recent study examines the association between alcohol use and dementia risk, as well as changes in drinking patterns. The results may help shape health advice on drinking.
Earlier research showed that dementia is more likely in people who drink heavily, while mild to moderate drinking is associated with a lower risk. Not much is known about how changes in the consumption of alcohol are related to dementia risk. Most studies use a snapshot design with a single assessment of alcohol consumption.
The current study, published in JAMA Network, examined a cohort of almost four million people in South Korea, with a mean age of 55. The data came from the Korean National Health Insurance Service database, comprising information logged in from two examinations performed in 2009 and 2011.
The aim was to assess the effect of changing patterns of alcohol consumption on the dementia risk compared to both teetotallers and those who continued to drink heavily. Almost equal parts of men and women comprised the study. None had pre-existing dementia, cancer or cardiovascular disease, and none died within a year of the second examination.
Levels of alcohol consumption were classified as none, mild, moderate, and heavy. These categories made up ~55%, ~27%, 11%, and ~7%, respectively. The latter three correspond to <15, 15-29.9, and 30 g/day, respectively.
Over the two years between examinations, changes in alcohol consumption were classified as non-drinkers, quitters, reducers, sustainers and increasers – the terms are self-explanatory. Approximately a quarter of mild drinkers, ~8% of moderate and ~7.5% of heavy drinkers quit drinking. Conversely, increasers made up 14% of non-drinkers, ~16% of mild and ~17% of moderate drinkers.
Among those who remained teetotallers throughout, the mean age was the highest, with three out of four being female and ~85% being non-smokers. Among quitters, too, the mean age was higher; more were female and non-smokers, more likely to exercise regularly and had lower incomes.
The researchers looked for new cases of Alzheimer’s disease (AD), vascular dementia (VD) or other dementia in the whole cohort stratified by drinking patterns and changes in such patterns.
What did the study show?
There were just over 100,000 cases of dementia from all causes, including almost 80,000 AD and ~11,000 VD cases.
When compared to teetotallers, the risk of dementia was reduced by a fifth among those who continued to drink mildly throughout the two years between examinations. Among sustained moderate drinkers, the reduction was comparable, at ~17%. Heavy drinkers had a small increase in all-cause dementia risk by 8%.
When compared to sustainers at the corresponding level of consumption, those who reduced their heavy drinking to moderate levels had ~10% lower risk of dementia from any cause, but 12% reduction in the AD risk. Similarly, those who began to drink mildly had the same level of risk reduction, with the same comparison group.
Those who stopped drinking and those who increased their drinking both showed a higher risk compared with those who continued to drink at the same level. Those who moved from mild to moderate, and from moderate to heavy drinking, respectively, showed a 9% and 16% increase in dementia risk, respectively. The greatest increase in risk, by 37%, was among those who drank mildly at first but moved into heavy drinking by the second examination.
The AD and VD proportions did not change significantly.
In a subgroup for which alcohol consumption data was available at a third timepoint four years after the first, there was a 25% reduction in risk among those who continued to drink at mild or moderate levels compared to teetotallers. Similarly, those who had begun to drink at this level by the second examination and continued to do so two years later showed an 18% reduction in risk. Those who had quit in 2011 and remained quitters in 2013 had a higher risk of dementia.
What are the implications?
The findings of the study indicate a lower risk of dementia among those who drink mildly to moderately when compared with lifelong or long-term teetotallers. Again, when heavy drinkers dropped their level of consumption to moderate levels, the risk of dementia was reduced.
For the first time, the study suggests a reduction in dementia risk among those who began to drink lightly after the baseline examination. The researchers add a caveat that self-reported alcohol consumption is typically underestimated, however.
These findings suggest that the threshold of alcohol consumption for dementia risk reduction is low.”
There is a steep increase in dementia risk once the threshold of heavy alcohol consumption is crossed, yielding a J- or U-shaped association. Among those who drank heavily and regularly, the risk was increased.
Alcohol in mild to moderate quantities may reduce neuroinflammation, improve platelet function and increase the level of high-density lipoprotein (‘good cholesterol’). In excess, though, alcohol is a nerve poison and induces a deficiency of many essential nutrients. High alcohol levels also enhance the accumulation of the abnormal tau protein in the brain, along with the death of cholinergic neurons, leading to a relative loss of acetylcholine, an important neurotransmitter molecule.
The study does not explore disease and death from non-dementia-causes related to alcohol consumption. This, coupled with the high addictive potential of alcohol, might explain why most medical guidelines discourage drinking at any level, even for health reasons.
In addition, individual metabolism and constitutive acetaldehyde dehydrogenase phenotypes determine a person’s susceptibility to alcohol and how well people can tolerate the beverage, making it almost impossible to predict the outcome on an individual basis.
A confounding effect in this study might come from the fact that much drinking is carried out at social gatherings, which are known to be associated with reduced dementia risk. Secondly, many or most people who quit alcohol do so because they become sick, often with cardiometabolic disease, which could explain the higher risk of dementia among abstainers. Finally, the higher risk among abstainers could be explained by their higher age and female sex, both of which are dementia risk factors.