It is the first large study to explore the link, and it adds to the mounting body of evidence that the B vitamin might help ward off heart disease and strokes.
But the study's lead author and an outside expert warned that much more research is needed before concluding that women should increase their consumption of folate.
Folate is found in such foods as oranges, dark green leafy vegetables and beans and legumes. In the United States, it is also added to cereal and flour products to help prevent birth defects.
The new study, published in Wednesday's Journal of the American Medical Association, involved one large group of women ages 27 to 44 and another ages 43 to 70. They recorded their folate intake over an eight-year period during the 1990s. Participants did not have a history of high blood pressure.
Younger women who consumed at least 1,000 micrograms of folate a day — or 2 1/2 times the recommended daily allowance — were 46 percent less likely to develop hypertension than women who consumed the smallest amounts, or less than 200 micrograms.
The effect was less pronounced in older women, who saw an 18 percent reduced risk of high blood pressure from consuming high levels of folate.
"If these findings are confirmed by a large, randomized, controlled trial, it would suggest that folic acid, which is both safe and readily available, could be used as a preventative measure against high blood pressure," said the study's lead author, Dr. John Forman of Harvard-affiliated Brigham and Women's Hospital in Boston.
The study also found that women who got their folate from food alone, instead of from supplements, had difficulty consuming enough of the vitamin to show a significant reduced risk of high blood pressure.
American Heart Association spokesman Dr. Daniel Jones said the findings are intriguing and warrant more research. But he said many past studies that showed strong benefits from vitamins have produced disappointing results during more stringent research.
He cited research that showed that taking large quantities of vitamin E was probably worthless for heart patients and might even do harm by interfering with cholesterol-lowering drugs.
Previous research showing that folate could help prevent devastating birth defects of the brain and spinal cord led the U.S. government to mandate that all grain foods be fortified with folate starting in 1998. A federal study published last year linked that regulation to a decrease in heart disease and strokes.