Folate intake and the risk of incident hypertension among US women.

CONTEXT Folate has important beneficial effects on endothelial function, but there is limited information about folate intake and risk of incident hypertension. OBJECTIVE To determine whether higher folate intake is associated with a lower risk of incident hypertension. DESIGN, SETTING, AND PARTICIPANTS Two prospective cohort studies of 93,803 younger women aged 27 to 44 years in the Nurses' Health Study II (1991-1999) and 62,260 older women aged 43 to 70 years in the Nurses' Health Study I (1990-1998), who did not have a history of hypertension. Baseline information on dietary folate and supplemental folic acid intake was derived from semiquantitative food frequency questionnaires and was updated every 4 years. MAIN OUTCOME MEASURE Relative risk of incident self-reported hypertension during 8 years of follow-up. RESULTS We identified 7373 incident cases of hypertension in younger women and 12,347 cases in older women. After adjusting for multiple potential confounders, younger women who consumed at least 1000 microg/d of total folate (dietary plus supplemental) had a decreased risk of hypertension (relative risk [RR], 0.54; 95% confidence interval [CI], 0.45-0.66; P for trend <.001) compared with those who consumed less than 200 microg/d. Younger women's absolute risk reduction (ARR) was approximately 8 cases per 1000 person-years (6.7 vs 14.8 cases). The multivariable RR for the same comparison in older women was 0.82 (95% CI, 0.69-0.97; P for trend = .05). Older women's ARR was approximately 6 cases per 1000 person-years (34.7 vs 40.4 cases). When the analysis was restricted to women with low dietary folate intake (<200 microg/d), the multivariable RR for younger women with total folate intake at least 800 microg/d compared with less than 200 microg/d was 0.55 (95% CI, 0.32-0.94; P for trend = .03), and 0.61 (95% CI, 0.34-1.11; P for trend = .05) in the older cohort. Among women who did not take folic acid-containing supplements, dietary folate intake of 400 microg/d or more was not significantly associated with risk of hypertension. CONCLUSION Higher total folate intake was associated with a decreased risk of incident hypertension, particularly in younger women.