Low to moderate consumption was defined as less than eight drinks per week for women and less than 15 drinks per week for men.
The findings support previous research that found that overall, one standard drink a day for women and two a day for men, which is America's guide, appears to offer some cognitive benefits.
"There is now a lot of observational evidence showing that drinking mild to moderate alcohol is associated with better cognitive function and a lower risk of dementia compared to alcohol withdrawal," said lead principal investigator scientist Kaarin Anstey, director of the Center for NHMRC dementia for Research Collaboration in Australia, which was not involved in the study.
"What we know for sure is that drinking too much alcohol definitely damages the brain in a major way. What's less clear is whether low or moderate intake may be protective in certain people, or whether total withdrawal is the best advice," said neurologist Dr. Richard Isaacson, founder of the Alzheimer's Prevention Clinic at NewYork-Presbyterian and Weill Cornell Medical Center.
"Based on conflicting studies, I don't think at this point we can know for sure whether none versus low to moderate consumption is better for each person," said Isaacson, who was not involved in any of the studies.
Not protective for African Americans
The study participants, who were predominantly white, female, and an average age of 62, received cognitive tests from 1996 to 2008, and were surveyed every two years for approximately nine years.
Compared to those who said they never drank, low to moderate drinking was associated with significantly higher cognitive scores for mental state, word recall, and vocabulary over time, as well as lower rates of decline in each of those areas.
Interestingly, the new study did not find that the cognitive benefit was true for African Americans.
"Few studies have evaluated whether the effects are similar across different racial or ethnic groups," Anstey said. "This [finding] raises the possibility that ethnic groups vary in their vulnerability to the cognitive effects of alcohol."
"This may make sense because of the increased likelihood of medical comorbidities like diabetes in blacks," said Isaacson.
However, Anstey cautioned, there are fundamental factors to consider before concluding that alcohol consumption varies by race.
"Alcohol consumption patterns are associated with socioeconomic status and other cultural factors," he said. "It is very difficult to separate the biological from the social mechanisms at play here."
In the end, this new study doesn't change what most doctors already recommend, experts say.
"In my clinical practice, I look at the totality of the evidence and then I individualize the recommendations for the person being served," said Isaacson.
For women, an overall maximum goal is four to six drinks per week at their Alzheimer's prevention clinic, she said. In men that would be 10 to 12 servings per week.
"But this is not a 'one size fits all' option," added Isaacson. "These decisions should be tailored based on body weight, for example, and also modified based on whether the person has a history of alcohol or substance abuse.
"Also, it's not just about 'what and how much' alcohol, it's also important to consider 'when and how' alcohol is consumed," Isaacson said.
For example, having a glass of wine with an early dinner is "more sensible than two glasses late at night on an empty stomach near bedtime," he said.
"Alcohol at bedtime tends to lead to poorer overall sleep quality, which also affects the risk of dementia," he added.
"I think for those who drink alcohol, they should follow the national guidelines as a guide to the maximum level of safe drinking," Anstey said, adding that this would not apply to anyone with a health condition that requires alcohol withdrawal.
And if you're not a drinker, don't start, she said.
"Drinking alcohol, for example, increases the risk of some cancers. If you don't drink, then we wouldn't recommend drinking alcohol."