Young women who consume more than 800 micrograms (ug) of folate per day can reduce their risk of developing high blood pressure by almost a third compared to those who consume less than 200 ug/day, according to new research presented at the American Heart Association's 58th Annual High Blood Pressure Research Conference.
Folate also reduced the risk in older women to a lesser degree.
Folate is a B-vitamin found in citrus fruits; tomatoes; leafy green vegetables such as spinach and romaine lettuce; pinto, navy, and kidney beans; and grain products. Since January 1998, wheat flour has been fortified with folic acid, the synthetic form of folate, to add an estimated 100 ug per day to the average diet.
Researchers studied more than 150,000 women to determine if there was a link between risk of high blood pressure and their level of folate intake, including supplements. Folate intake was examined in quintiles. They studied two age groups -- women 26-46 years old, and 43-70. Researchers found the most dramatic effects among the younger group.
Younger women in the highest folate intake quintile (consuming more than 800 ug/day) of total folate (dietary intake plus supplements) had a 29 percent lower risk for high blood pressure than those in the lowest quintile (consuming less than 200 ug/day of folate). Older women who had total folate intake of 800 ug/day had a 13 percent lower risk.
Folate has been shown to reduce levels of homocysteine, a blood component that can damage blood vessels. Folate may also help blood vessels relax, improving blood flow, said John P. Forman, M.D., lead author of the study and a research and clinical fellow at Brigham and Women's Hospital in Boston.
The benefit of folate was independent of other factors such as exercise, salt intake and diet, which are known to influence risk of high blood pressure.
Forman and colleagues based their finding on data collected in two large studies of women -- the Nurses' Health Study I, which includes 62,260 women, ages 43-70 and the Nurses' Health Study II, which includes 93,034 women ages 26-46. None of the women had a history of high blood pressure when the study started.
Using a semi-quantitative food frequency questionnaire the researchers gathered information about dietary and supplemental folate intake at baseline, then followed up with additional questionnaires every four years. Information about physician-diagnosed high blood pressure was self-reported on health status questionnaires every two years during eight years of follow-up.
The researchers also collected data on body mass index; exercise; smoking; family history of hypertension; salt; calcium, magnesium and potassium intake; fiber intake; methionine intake; caffeine and alcohol consumption; and use of vitamins B6, B12 and D.
The Food and Drug Administration began requiring folate supplementation of several foods, including cereals and bread, in 1998. But, fortification began in 1996, spanning the last two years of the NHS I and the last three years of the NHS II.
Researchers also looked at the independent effect of supplemental folic acid by analyzing the subset of women with very low dietary intake of folate. Women in NHS II who consumed 800 ug/day or more of folate (comprised primarily of supplemental folic acid) had a 48 percent reduction in hypertension risk compared to those whose folate intake was less than 200 ug/day (and who did not take supplements). Women in NHS I had a 40 percent reduction.
The co-authors of the study are Eric B. Rimm, Sc.D.; Meir J. Stampfer, M.D., Dr. P.H.; and Gary C. Curhan, M.D., Sc.D.