Tina Hoang of The Veterans Health Research Institute, San Francisco, and the University of California, San Francisco, and colleagues tracked more than 1,300 women age 65 and older for 20 years.
They measured frequency of current and past alcohol use at the beginning, midpoint -- years six and eight -- and late phases -- years 10 and 16 -- of the study.
Hoang said previous research had found light to moderate alcohol consumption -- seven to 14 drinks/week -- has generally been considered to have some health benefits, including possibly reducing risk of cognitive decline later in life.
The study found moderate drinkers at baseline or at midpoint had similar risk of cognitive impairment to non-drinkers; but moderate drinkers in the late phase of the study were roughly 60 percent more likely to develop cognitive impairment.
Women who changed from non-drinking to drinking during the course of the study had a 200 percent increased risk of cognitive impairment, the study said.
"In this group of older women, moderate alcohol consumption was not protective," Hoang said. "We found that heavier use earlier in life, moderate use in late-life, and transitioning to drinking in late-life were associated with an increased risk of developing cognitive impairment. These findings suggest that alcohol use in late-life may not be beneficial for cognitive function in older women."
The findings were published in the Alzheimer's Association International Conference in Vancouver.