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 93803 younger women aged 27 to 44 years in the Nurses' Health Study II (1991-1999) and 62260 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 12347 cases in older women. After adjusting for multiple potential confounders, younger women who consumed at least 1000 mug/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 mu g/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 mug/d), the multivariable RR for younger women with total folate intake at least 800 mug/d compared with less than 200 mug/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 mug/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.