Here's good news for women who love coffee: Drinking it doesn't seem to cause long-term high blood pressure, a study suggests.

But for some reason, women in the same study who drank colas did seem to have a greater risk of high blood pressure. Researchers were surprised at that and cautioned that the study wasn't conclusive.

Caffeine is a well-known ingredient in both beverages, and has been shown to cause short-term increases in blood pressure. But coffee drinkers in the study were no more likely than abstainers to develop high blood pressure during 12 years of follow-up.

Previous data on coffee and hypertension is mixed, but there's a common perception that its temporary effects on blood pressure mean an increased long-term risk, said Dr. Wolfgang Winkelmayer, the study's lead author and a researcher at Boston's Brigham and Women's Hospital.

"We found strong evidence to refute" that belief, the researchers wrote.

There was even some evidence that women who drank lots of coffee — four or more daily cups of regular or decaf — faced a slightly lower risk for developing high blood pressure than those who drank little or none.

Winkelmayer said that may be because coffee has lots of antioxidants, substances which are thought to help protect the heart and reduce risks of cancer.

He called the results for cola drinkers surprising and potentially worrisome, but also far from definitive because it's unclear how sodas might increase blood pressure.

The government-funded study appears in Wednesday's Journal of the American Medical Association.

Several recent studies have shown possible health benefits from coffee, including a report calling it a major food source for antioxidants; results linking heavy coffee consumption in men with a reduced risk of diabetes; and Japanese research suggesting that coffee might help prevent liver cancer.

Winkelmayer's group examined data on 155,594 mostly white female nurses aged 55 on average who took part in two long-running health studies. They were questioned periodically about their diets and health and followed over 12 years. About 33,000 were diagnosed with high blood pressure.

Women who drank more than three cups of coffee daily were about 7 percent to 12 percent less likely to develop high blood pressure than women who drank little or no coffee.

Those who drank at least four cans of sugared cola drinks daily had a 28 percent to 44 percent increased risk of high blood pressure, compared with women who drank few or none. Diet sodas also increased the risk, although slightly less than the non-diet drinks.

Dr. Charalambos Vlachopoulos, a lecturer at Athens Medical School in Greece whose research has linked coffee with mainly negative cardiovascular effects, said the results "don't necessarily apply" to others, including men and women of other ages and races.

Nutritionist Margaret Savoca, whose work has linked caffeinated soft drinks with higher blood pressure in black teenagers, said she suspects caffeine explains Winkelmayer's results in heavy cola drinkers, too.

Women who drink a lot of soda might have other characteristics that make them different from those who drink lots of coffee, and caffeine might affect them differently, said Savoca, of the University of North Carolina in Greensboro.

Sodium might also be a culprit, said Dr. William Frishman, chief of medicine at Westchester Medical Center in Valhalla, N.Y.

Though a single can of soda doesn't have much salt, drinking lots of soda can add up and high blood pressure was most common in those who drank four or more cans daily.

"No one's going to say that cola is dangerous," said Frishman, who added: "It should be consumed in moderation."