Researchers found that people who consumed at least 300 micrograms (mcg) of folate per day had a 20 percent lower risk of stroke and a 13 percent lower risk of cardiovascular disease than those consuming less than 136 mcg of folate per day. The findings accounted for other heart disease risk factors such as cholesterol, blood pressure, smoking, and obesity.
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 mcg per day to the average diet.
"Our data support the existing recommendation to consume 400 mcg of folate per day," says the study’s lead author Lydia A. Bazzano, Ph.D., a research fellow at Tulane School of Public Health and Tropical Medicine in New Orleans.
For consumers, Bazzano says the results of this study mean that it is likely that dietary intake of folate can affect the risk of stroke. "Therefore, people should be aware of the amount of folate in their diets," she says. "For doctors, this study would suggest that screening patients’ dietary folate intake and promoting the recommended level may decrease patients’ risk of stroke." Folate is thought to have beneficial effects on the cardiovascular system by decreasing levels of homocysteine, an amino acid that is linked to a higher risk of atherosclerosis. Atherosclerosis is the disease process that underlies heart disease and stroke. Folate can reduce homocysteine, but this new study looks at the direct effect of folate on cardiovascular disease risk, according to Bazzano.
Researchers looked at participants in the National Health and Nutrition Examination Survey I Epidemiologic Follow-up Study (NHEFS) to examine the relationship of dietary folate intake to the risk of cardiovascular disease.
Study participants included 9,764 men and women in the United States, ages 25 to 74 years. They did not have cardiovascular disease when the study started. In the original study, researchers asked participants to recall the food they had eaten during the last 24 hours. Specific dietary intake of folate was not available in the first database, but researchers later matched the recorded foods and portions to foods listed in a database to estimate the amount of folate ingested by patients in a 24-hour period.
According to the study, follow-up data were collected between 1982 and 1984, and in 1986, 1987, and 1992. Each follow-up examination included performing an in-depth interview; obtaining hospital and nursing home records, including pathology reports and electrocardiograms; and, for those who died during the study, acquiring a death certificate. The researchers recorded incidences of stroke and cardiovascular disease that occurred during follow-up.
The results showed participants’ median folate intake was 203.7 mcg per day. Compared with those with a lower intake, people who consumed more folate tended to be male and white. Participants with higher folate intake had, on average, slightly lower systolic blood pressure and lower total cholesterol levels than those who ate less folate.
After adjusting for history of diabetes, systolic blood pressure, cholesterol levels, body mass index, recreational physical activity, levels of education, alcohol consumption and current cigarette smoking, dietary folate was significantly and inversely related to the risk of stroke and cardiovascular disease. From 1971 to 1992, participants had experienced 926 strokes and 3,758 cardiovascular events. The inverse relationship between dietary folate and incidence of stroke and cardiovascular disease was consistent across genders, levels of physical activity and tobacco use.
Bazzano says a limitation of the study was estimating dietary folate intake based on participants recall of foods they had eaten in a single 24-hour period. "Because of the day-to-day variation in diet it can be harder to find an association using this method; therefore, our findings may underestimate the strength of the association."
The American Heart Association recommends that adults take 400 mcg of folate (vitamin B9) a day and pregnant women take 600 mcg a day. Stroke is the third leading cause of death and a leading cause of serious long-term disability in the U.S. general population. In an editorial accompanying Bazzano’s study, Scott Kasner, M.D., director of the Comprehensive Stroke Center at the University of Pennsylvania Medical Center, says, "This study adds to our knowledge about a link between higher dietary intake of folic acid and a lower risk of stroke. Further research is still needed to clarify the optimal amount of folic acid and identify which patients require additional supplementation. In the meantime, we should recommend 300 to 400 micrograms of folic acid for people at risk for cerebrovascular and cardiovascular disease."
Co-authors are Jiang He, M.D., Ph.D.; Lorraine G. Ogden, M.S.; Catherine Loria, Ph.D., M.S.; Suma Vupputuri, Ph.D.; Leann Myers, Ph.D.; and Paul K. Whelton, M.D., M.Sc.
This research was supported in part by a grant from the National Heart, Lung, and Blood Institute.
NR02 – 1068 (Stroke/Bazzano)
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