Australia recommends no more than two for men and women.
The Harvard study found the greatest benefit, at around 50 per cent, was for people who drank on most days.
"The data suggests that regular, moderate consumption of alcohol at mid-life may be related to a modest increase in overall health status," the researchers say in the journal Proceedings of the Library of Science, Medicine.
But they warn that their findings relate only to middle-aged women, not men, because of the "distinct health effect of alcohol between men and women".
The idea that moderate drinking may be good for health is well entrenched, but has been increasingly questioned, including by New Zealand epidemiologists Professors Jennie Connor and Rod Jackson, who challenged the theory in Britain's Lancet journal in 2005.
Professor Connor, of Otago University, told the Science Media Centre the Harvard study added nothing to the many similar studies that were "unreliable for answering questions about the health effects of drinking because of their design".
The supposed health benefit might be due to differences in lifestyle - other than drinking - that were associated with being a low-risk drinker.
"It may be true that women who drink one drink a day are healthier than others, but we do not know if it has anything to do with the alcohol, as these women are not the same as others in a variety of ways."
There was no scientific justification for the promotion of alcohol as health-enhancing for any sub-group of the population.
"The potential for harm is great, and the potential for good is unknown."
THE STUDY
* Harvard University researchers checked the health at age 70 or older of nearly 14,000 women, and related this to drinking in their late 50s.
The conclusion
* Women who had drunk half to three standard drinks a day had a 20 to 30 per cent greater chance than non-drinkers of being in good overall health when older.
