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 Journal of 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 United States, and prevalence is increasing as population ages. Blood pressure is influenced by openness and elasticity of blood vessels; HTN indicates loss of elasticity, narrowing of vessels, or both. It is frequently caused by plaque formation along inner vessel walls (atherosclerosis). Because heart pumps against resistance (pressure) of arteries, HTN increases work heart must do to keep blood flowing to all parts of body. Chronic HTN can therefore cause thickening of heart muscle and eventual heart failure. HTN also increases risk of stroke and kidney failure. Preventing HTN is critical to reducing incidence of heart disease, leading cause of death in 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 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 health of vessel walls and lower blood pressure.

Data from two previous studies of health and disease patterns in women in US, known as Nurses' Health Study I and II, were used in current study to examine effect of dietary and supplemental folic acid intake on HTN.