CHICAGO — High folate intake may lower the risk of hypertension, particularly in young women, according to data presented at a conference of the Council for High Blood Pressure Research.
Young women who consumed at least 800 mcg/day of folate reduced their risk of developing high blood pressure by almost a third, compared with those who consumed less than 200 mcg/day. Folate also reduced the risk in older women to a lesser degree, reported John P. Forman, M.D., a research and clinical fellow at Brigham and Women's Hospital in Boston.
The most striking effects of folate intake were seen among women aged 35 years or younger, he said. Supplemental folic acid also contributed to this decrease in risk, as most of the women in the higher range of folate intake obtained much of their intake from supplements.
Dr. Forman and colleagues based their findings on data from the Nurses' Health Study (NHS) I, comprising 62,260 women aged 43–70 years, and the NHS II, comprising 93,034 women aged 26–46 years. None of the women had high blood pressure at baseline.
Semiquantitative food-frequency questionnaires were used to gather information about dietary and supplemental folate intake at baseline, and were followed up with additional questionnaires every 4 years. Information about physician-diagnosed high blood pressure was self-reported every 2 years.
Cox regression analysis was used to estimate relative risk after the investigators controlled for age, body mass index, smoking, exercise, family history of hypertension, and intake of alcohol, caffeine, salt, calcium, magnesium, potassium, fiber, methionine, and vitamins B6, B12, and D.
Over 8 years of follow-up, there were 12,347 incident cases of hypertension in NHS I and 7,373 incident cases in NHS II.
Young women who consumed at least 800 mcg/day of folate had a 29% lower risk of high blood pressure than did those who consumed less than 200 mcg/day. Older women who consumed at least 800 mcg/day had a 13% lower risk than did those who consumed less than 200 mcg/day.
There was no significant interaction between age and reduced risk among women in the older cohort when divided into three additional subgroups.
One hypothesis for why the effect of folate varies by age is that the pathogenesis of hypertension may be different in older versus younger women, Dr. Forman said at the meeting, sponsored by the American Heart Association.
The Food and Drug Administration began requiring folate supplementation of several foods, including bread and cereals in 1998. But fortification had begun in 1996, spanning the last 2 years of the NHS I and the last 3 years of the NHS II.
The researchers did not directly measure serum folate, which was a limitation of the study, Dr. Forman said. However, the food-frequency questionnaires used in the cohort have been previously validated and are highly correlated with both dietary records and serum folate levels. Additionally, all of the study participants were registered nurses, and self-reported hypertension was thought to be reliable.