高量葉酸攝取可降低女性罹患高血壓的風險


  Jan. 18, 2005 -- 根據JAMA期刊1月19日所載,藉由飲食或其他的營養補給方式來攝取大量的葉酸,可以明顯降低女性的高血壓罹患率。
  
  來自布萊根婦女醫院及哈佛醫學院的John P. Forman及其同事指出,根據兩項小型的隨機活體試驗顯示,口服的葉酸補給可以改善內皮組織的功能,高劑量的葉酸有助於降低血管的收縮壓及舒張壓;這些資料總合顯示,攝取大量的葉酸可以降低罹患高血壓的風險。
  
  在一為期8年的試驗裡,研究人員將無高血壓病例的婦女們以年齡分為兩組,進行葉酸攝取與高血壓之間的關係評估;93803位女性年齡在25到42歲之間(平均36歲)的試驗者為一組,另一組有62260位,年齡在30到55歲之間(平均55.4歲);該性研究計畫名為Nurses' Health Study II (1991-1999)。
  
  以半計量式的食物頻率問卷調查來進行飲食中的葉酸,或葉酸的營養補給品攝取評估;問卷調查分別在試驗初期、第4年、第8年時進行;高血壓的調查則以自我報告的方式讓試驗者在問卷中提出,頻率為兩年一次;聯邦政府在1998年所公佈的食物供給法案中包含了葉酸的增量攝取規範,這個因素也在本項分析結果中作過調整。
  
  回歸分析顯示,相較於每日低於200μg者,年輕的女性每日攝取1000μg以上的葉酸,其高血壓的罹患風險會降低46%(相對風險0.54,絕對風險降低8例/1000例每年)。
  
  葉酸攝取的效果在年長的婦女身上較不明顯,相較於每日低於200μg者,年長的女性每日攝取1000(g以上的葉酸,高血壓罹患率的降低程度為18%(相對風險0.82,絕對風險降低6例/1000例每年)。
  
  每日從食物攝取葉酸低於200μg的婦女可以使用營養補給品,另行補充800μg,如此也可以降低高血壓的風險;這一方面,年輕的女性效果比較好(相對風險0.61)。
  
  Forman醫師表示,經過變因調整後,結果仍然顯示,較高的葉酸攝取量明顯的降低高血壓的罹患率;調整的變因,包含食物攝取、身體活動力、身體質量指數及家庭病史等;對照組的上限值由每日200μg升到400μg以後(官方每日建議攝取量),本項試驗的逆向分析結果維持不變。
  
  該項研究的限制因素,包括此試驗為一觀察性的試驗,依靠自我報告結果,未對血壓作篩選,未對血液葉酸濃度作評估。
  
  Forman醫師總結指出,就目前所知,本試驗是第一個致力於高血壓與葉酸的關係研究;未來的研究的重點是,證明葉酸可以安全有效的降低年輕女性的血壓,甚至預防高血壓的發生。

High Folate Intake May Reduce<

By Yael Waknine
Medscape Medical News

Jan. 18, 2005 — High folate intake from dietary and supplemental sources significantly decreases the risk of incident hypertension in women, especially younger women, according to the results of two prospective, observational cohort studies published in the Jan. 19 issue of JAMA.

"Oral folic acid supplementation improves endothelial function in vivo...[and] 2 small randomized trials have demonstrated that high-dose folic acid supplementation may lower systolic and diastolic blood pressure," write John P. Forman, MD, from Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, and colleagues. "Taken together, these data suggest that a higher intake of folate may reduce an individual's risk of hypertension."

The investigators prospectively evaluated the association between folate intake and incident hypertension over eight years in two age-based cohorts of women with no history of hypertension. The cohorts were made up of 93,803 women aged 25 to 42 years (mean, 36.0 years) and 62,260 women aged 30 to 55 years (mean, 55.4 years) enrolled in the Nurses' Health Study II (1991-1999) and I (1990-1998), respectively.

Dietary and supplemental folate intakes were assessed using a semiquantitative food frequency questionnaire at baseline, four, and eight years. Incidence of hypertension (as per physician diagnosis) was self-reported by biennial questionnaire. Subsequent analysis included adjustments for increased dietary folate due to the federally mandated fortification of the food supply completed in 1998.

Regression analysis showed that younger women consuming at least 1,000 µg per day of total folate (dietary plus supplemental) had a 46% reduction in the risk of incident hypertension (relative risk [RR], 0.54; 95% confidence interval [CI], 0.45 - 0.66; P < .001; absolute risk reduction [ARR], 8 cases/1,000 person-years) compared with those ingesting less than 200 µg per day.

The effect of high folate intake on the risk of incident hypertension was less pronounced in the older cohort. Older women consuming more than 1,000 µg per day of total folate had an 18% reduction in the risk of incident hypertension (RR, 0.82; CI, 0.69 - 0.97; P = .05; ARR, 6 cases/1,000 patient-years) compared with those ingesting less than 200 µg per day.

Supplementation to achieve total folate intake of 800 µg per day or higher also reduced the risk of incident hypertension in women with low dietary folate (< 200 µg/day), with a more pronounced effect in the younger cohort (RR, 0.55; 95% CI, 0.32 - 0.94; P = .03) than the older cohort (RR, 0.61; 95% CI, 0.34 - 1.11; P = .05).

"Higher total folate intake was significantly associated with a reduced risk of incident hypertension even after controlling for a large number of covariates including dietary intake, physical activity, [body mass index], and family history," the authors write, adding that the inverse association remained robust even after changing the upper limit of the reference group from 200 µg per day to 400 µg per day, the U.S. recommended daily allowance.

Limitations of the study include its observational nature and reliance on self-reported data, with no regulation of blood pressure screening or evaluation of serum folate levels.

"[T]o our knowledge, this is the first prospective study to report an association between folate intake and the risk of incident hypertension," the authors conclude, noting the need for future trials examining folic acid as a readily available and safe means of lowering blood pressure and preventing hypertension in young women.

The study was funded by the National Institutes of Health.

JAMA. 2005;293:320-329

Reviewed by Gary D. Vogin, MD

    
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