Texans living in "dry" counties are more likely to suffer heart attacks and congestive heart failure than people living in nearby "wet" counties, where alcohol sales are legal, a new study reports.
But they're also less likely to suffer from atrial fibrillation, a condition where irregular heart rhythms raise the risk of stroke.
"It appears that alcohol is not necessarily all good or all bad for the heart -- it's more complex than that," said senior author Dr. Gregory Marcus, director of clinical research for the University of California, San Francisco Division of Cardiology.
"One size does not fit all," Marcus added. "These data suggests that there may be some in whom alcohol -- presumably in moderation -- would be of benefit, and others where it would do harm."
Residents of wet Texas counties, for instance, have a 9 percent lower risk of heart attack and 13 percent lower risk of congestive heart failure, according to the study.
But there was a downside, too: folks with easy access to alcohol appeared to have a 5 percent greater risk of atrial fibrillation, the researchers found.
Cardiologists have long debated whether alcohol can be good or bad for the heart. Some previous studies have found that moderate alcohol consumption -- two drinks a day for men, one for women -- might reduce heart attack risk, but overall the data has been inconsistent, researchers said in background notes.
For their own comparison, Marcus and his colleagues focused on Texas, where "local option" laws give individual counties the power to outlaw alcohol sales.
They analyzed medical data on more than 1.1 million hospitalizations recorded between 2005 and 2010 among Texans 21 or older. They sorted patients based on whether they lived in a dry or wet county.
The researchers found that people living in a wet county were 36 percent more likely to drink too much.
They also found that wet county residents appeared less likely to suffer heart attacks or heart failure, but more likely to develop atrial fibrillation.
"I suspect this suggests that some are at greater risk and others may be more prone to benefit," Marcus said. "For example, if a patient has a propensity to develop atrial fibrillation, alcohol, even in moderation, may be harmful for that person."
On the other hand, "if someone is at low risk for AF and yet high risk for a heart attack, perhaps due to genetic variants that mediate such risk, then moderate alcohol consumption could yet be helpful for that person."
The researchers aren't sure why alcohol might cause atrial fibrillation. But it has been noted that people can develop an irregular heartbeat following heavy alcohol consumption, said Dr. Richard Stein, director of the Urban Community Cardiology Program at the New York University School of Medicine.
The phenomenon is common enough that it has its own nickname, the "holiday heart syndrome," Stein said.
Alcohol's potentially beneficial effects on heart health also remain a mystery, although some have speculated it could be tied to a reduction in blood cholesterol levels, Stein said.
Stein noted that the increased risk of atrial fibrillation was "very small" in this study.
"They didn't really in my mind prove that it isn't a statistical phenomenon, or might not be due to some other factor that they didn't correct for," he said.
Studies like this can't prove a direct cause-and-effect relationship between alcohol and heart health because they are observational, not a carefully controlled clinical trial, Stein said. He added that it's unlikely there ever will be a clinical trial on this matter, since it would involve asking some people to drink who otherwise wouldn't.
These findings won't alter Stein's advice for patients.
"If you don't drink, and your doctor says it may help you avoid a heart attack if you have one glass of wine at night, but you don't really enjoy it, I would stay away from it," he said. "If you are drinking two glasses of wine three times a week, I would not worry about it. I would continue to drink at that low level."
There are plenty of other ways to improve your heart health, Stein said. He cited eating a healthy diet and exercising regularly, for example.
The findings were published online June 14 in the British Medical Journal.