If you're worried that drinking alcohol could raise the risk of dementia as you get older, a large new study from South Korea can provide some insights. That starts with the idea that in general, cutting down on alcohol is a good idea.

"Maintaining mild to moderate alcohol consumption is associated with a decreased risk of dementia, whereas heavier drinking increases the risk of dementia," the study's first author, Dr. Keun Hye Jeon, told NPR.

One part of the study's conclusions seems to have surprised many people: It found that while dropping from heavy to moderate alcohol consumption lowered the risk of dementia, so did the "initiation of mild drinking."

Study sees a complex interaction of alcohol and health

"Those who drink alcohol within the recommended guidelines are not advised to stop on the grounds of reducing the risk of dementia," Jeon said, "although cutting back on alcohol consumption may bring other health benefits."

Compared to people who didn't change their alcohol habits, Jeon and her colleagues found that two groups showed a heightened risk of dementia: drinkers who increased their consumption, and people who quit altogether.

"Quitters from any level of alcohol consumption showed higher risk of all-cause dementia compared with those who sustained the same level of drinking," according to the research paper.

Much has been made of that aspect of the findings, as people try to parse whether it might represent a true cause and effect — and a possible new data point in their own decisions about drinking. But the researchers warn that the higher dementia risks of people who quit drinking in their study "are suspected to be primarily attributed to the sick quitter effect, which is defined as a person quitting (or reducing) a certain hazardous activity because of health issues."

In other words, they may have quit drinking because their health worsened, rather than their health worsening because they quit drinking.

So, what can drinkers do to limit their risk of dementia?

When asked what surprised researchers the most in the results, Jeon says it's the steep drop in risk when people cut back on alcohol, noting that heavy drinkers who moderated their intake were associated with an 8% decrease in risk for dementia from all causes, and a 12% decreased risk of Alzheimer's disease.

"For the prevention of dementia, mild-to-moderate drinkers need to curb the increase in their alcohol consumption, while heavy drinkers should reduce it," said Jeon, an assistant professor of family medicine at CHA University in Gumi.

"People who do not currently drink alcohol should not be encouraged to start as a way to reduce dementia risk," she added.

Alcohol is known to damage brain cells and impair memory and other functions. Current U.S. dietary guidelines urge adults to "drink in moderation by limiting intake to 2 drinks or less in a day for men and 1 drink or less in a day for women."

A key takeaway from the study, the researchers say, is that it suggests that even small reductions in alcohol consumption can help reduce dementia risk.

The study included millions of adults

To look for potential associations between alcohol use and dementia outcomes, the researchers drew on data from the Korean National Health Insurance Service. The government-administered insurer offers free biennial health exams to every insured person age 40 and over.

The study included nearly 4 million South Koreans — a specific cohort of adults who had consecutive NHIS health exams in 2009 and 2011. The exams include a questionnaire on medical history and personal habits, including drinking, smoking and exercise, along with lab tests and demographic data.

The research team categorized people into four drinking categories: none; mild (less one drink per day); moderate (one to two drinks per day) and heavy (more than two drinks per day).

In the U.S., a standard drink is considered to contain 14 grams (0.6 ounces) of pure alcohol, slightly less than the 15 grams used in the study. That equals a 12-ounce beer at 5% alcohol, a 5-ounce glass of wine with 12% alcohol, or 1.5 ounces of an 80-proof spirit.

The researchers also sorted people according to whether they quit, reduced, sustained or increased their alcohol intake. Then, starting from one year after the second health exam, researchers tallied which members of the cohort had been diagnosed with dementia through the end of 2018.

The 'sick quitter' effect

"The sick quitter effect is based on the assumption that disease onset and changes in health condition lead to cessation of alcohol consumption," Jeon said, "so the risk for former drinkers is higher than that for abstainers."

In the study, former drinkers were mostly included in the nondrinker control group. But, she added, "The poor overall health of former drinkers may result in overestimation of the protective effect of alcohol consumption."

The study's authors tried to compensate for that dynamic in a number of ways, but "the sick quitter effect remains a source of potential bias," they wrote.

Another complicating factor is socioeconomic status. The study found that people who quit drinking tended to be older and and have lower incomes than people who maintained the same alcohol habits. On the plus side, the quitters did tend to be nonsmokers and were more likely to get regular exercise.

The Korean study also relied on people to report their own health habits, which researchers acknowledge as a limitation.

What does science say about alcohol intake?

Heavy drinking and binge drinking are linked to chronic liver disease, high blood pressure, several types of cancer, and a raft of other health problems, the CDC says. Excessive alcohol consumption also is associated with violence, accidental deaths and injuries, and harm to a developing fetus.

Outside of the U.S., some recent advisories are more stringent. A massive international study in The Lancet concluded in 2018 that "the safest level of drinking is none." And last month, Canada's newly updated guidelines caused a stir when it concluded that any level of alcohol consumption brings a risk, and that people should restrict themselves to two standard drinks or less each week.