Women who get lots of folic acid from both diet and supplements have less chance of developing high blood pressure than women who get very little, according to a study in the Journal of the American Medical Association (2005;293:320-9) that re-analyzed data from two previous studies.
Hypertension (HTN) is defined as blood pressure higher than 140/90 mm Hg. HTN affects approximately 65 million people in the United States, and the prevalence is increasing as the population ages. Blood pressure is influenced by the openness and elasticity of the blood vessels; HTN indicates loss of elasticity, narrowing of the vessels, or both. It is frequently caused by plaque formation along the inner vessel walls (atherosclerosis). Because the heart pumps against the resistance (pressure) of the arteries, HTN increases the work the heart must do to keep blood flowing to all parts of the body. Chronic HTN can therefore cause thickening of the heart muscle and eventual heart failure. HTN also increases the risk of stroke and kidney failure. Preventing HTN is critical to reducing the incidence of heart disease, the leading cause of death in the US. Public health recommendations are based on evidence that a diet rich in fruits and vegetables and low in saturated fats, combined with regular moderate exercise, can protect against HTN.
Folic acid, one of the B vitamins, occurs naturally in many plant foods (such as beans and green leafy vegetables) and is commonly found in multivitamins and B-complex supplements. Due to its role in preventing some birth defects, a number of foods are now fortified with folic acid, such as cold cereals and other grain products. Along with vitamins B6 and B12, folic acid lowers blood levels of homocysteine, an amino acid that has been found to be a heart disease risk factor. Several small studies have suggested that folic acid supplements might improve the health of the vessel walls and lower blood pressure.
Data from two previous studies of health and disease patterns in women in the US, known as the Nurses’ Health Study I and II, were used in the current study to examine the effect of dietary and supplemental folic acid intake on HTN.
More than 238,000 women participated in the two studies. One study included women between 25 and 42 years old and the other included women between 30 and 55 years old. Women in both studies answered questionnaires about health and dietary habits upon enrollment. For both studies, follow-up health questionnaires were filled out every two years for eight years, and a follow-up diet questionnaire was answered after four years.
The study involving younger women found that those who consumed the most total folic acid (more than 1,000 mcg per day) from both diet and supplements had a 46% lower risk of HTN than those who consumed the least total folic acid (less than 200 mcg per day). In the study with older women, consuming the most folic acid afforded an 18% risk reduction compared with consuming the least. In women whose dietary folic acid was less than 200 mcg per day, a combined dietary and supplemental folic acid intake of at least 800 mcg per day reduced HTN risk, relative to a combined intake of less than 200 mcg per day, by 45% in the study with younger women and 39% in the study with older women. In women who did not take supplements, getting the currently recommended 400 mcg per day from food was not protective against HTN in either study.
This analysis of the results from two studies provides evidence that folic acid can significantly reduce HTN risk in women. It further suggests that supplementing with folic acid is an effective way to increase intake to a level that protects against HTN. Future studies should further examine the relationship between folic acid intake and HTN risk, as well as the possible role for folic acid supplements in reducing blood pressure in people with HTN.